Industrial Instrumentation On Load Cells Engineering Essay

Load cells are detectors which are used to mensurate the degree or force per unit area by change overing the force ( torsion or mass ) into electrical signals and so these signals are displayed by the show unit to demo the degree or force per unit area. Load cells are besides known as burden transducers. In dictionary, a burden cell is known as â€Å" weight mensurating device necessary for electronic signal that displays weight in the signifier of figures. † Load cells can be classified harmonizing to their operations: Load cells that utilize liquid force per unit area or air force per unit area. Load cells that utilize snap. Load cells that utilize a magnetostriction or piezoelectric consequence. The strain gage burden cell is the largely used among the all sorts of burden cells. Therefore, when we say â€Å" burden cell, † we are largely mentioning to strive gauge burden cells. Although there are many other measurement devices, such as piezoelectric detectors, magnetostrictive detectors, electrical capacity detector and other detectors.1.2-Types of Load cellsStrain gage burden cells Tension burden cells Pneumatic burden cells Hydraulic burden cells Shear Load Cells Compression Load Cells Bending Load Cells Ringing Torsion Load Cells Pancake Load Cells Single Point Load Cells1.3-Strain Gauge Load CellsThis is a type of burden cell which is usage to mensurate the degree of any storage vas.1.3.1-Working ruleWhen force per unit area is applied on a music director its length alterations due to which opposition of the music director alterations and relation to the alteration in opposition show unit displays the alteration in degree.1.3.2-Construction and workingA strain gage is consists of a long length music director which is arranged in zig-zag manner on the flexible membrane which is exposed to the applied force per unit area country. This music director is connected in a wheat rock span as a resistance and when force per unit area or weight is applied on the membrane which is connected to the music director it gets stretched and due to stretching the length of the music director alterations and due to alter in length the opposition of the music director additions. These are normally four or a multiple of four, are connected into a wheat rock span constellation in order to change over the really little alteration in the opposition into the suited electrical signal. As these gages are combination of mechanical and electrical constituents so the mechanical parts are located at the site but electrical parts are in the control suites due to their environmental and temperature sensitivenesss. And the wires used for the transmittal of the signals besides have their ain opposition so that opposition besides considered during their building. The accommodation and arrangement of the strain gage burden cell in the wheat rock span and its working phenomena is shown in the undermentioned diagrams. Strain gage burden cells are placed at the underside of the vass largely to mensurate the degree of the column or vas. 00204.png Figure Figure 00205.png1.3.3-AdvantagesStrain gage burden cells are used in automotive industry to look into the structural public presentations of the stuff used in doors, goons, short pantss etc. Strain gage burden cells can be usage for weighing intents. Strain gage burden cells can besides be usage for stuff testing in procedure industry besides. Strain gage burden cells are besides used in tensile trial machines as a major constituent. Strain gage burden cells truth is 0.07 % of the rated capacity Strain gage burden cells can be used for both enlargement and compaction. Strain gage burden cells are less dearly-won so largely used in the industry.1.3.4-DisadvantagesStrain gage burden cells require uninterrupted electric energy for the production and show of signals. Strain gage burden cells besides requires an elaboration circuit for the coevals of end product show because the signals produced by the gage itself are of really much low electromotive force about in milli Vs. Strain gage burden cells can non be used for the force per unit area measuring of extremely reactive or caustic stuffs because they can damage the gage. Strain gage burden cells can non be used for the measuring of really high force per unit area if the stop usage is of plastic.1.4-Tension Load CellsThis is another type of burden cell which is besides usage to step to the degree.1.4.1-Working PrincipleIt consists of a vibrating wire transducer, fixed in a thick-vessel metallic cylinder, designed to supply a extremely stable and sensitive agencies of supervising tensile tonss in weighing systems, like procedure weighing systems and batch systems. As the applied burden additions on the burden cells the force on the internal vibrating wire besides increases by altering its tenseness, and therefore the resonating frequence of the vibrating wire. The frequence is measured and relative to the applied weight.1.4.2-Construction and workingThe chief portion of this burden cell is strain gauged stop which is for good secured in the transducer shell. The transducer is fitted with a metallic oculus leting in line connexion to the deliberation system, and a metallic hook, attached to the sensitive stop, provides a agency by which weight is applied in a suspended manner. The burden cell is vented to the ambiance to extinguish barometric effects for the upper limit or optimal truth. The signal overseas telegram which is attached to the burden cell is connected with the control room where these signals can be monitored. Figure There are besides some Thermistors placed inside its shell which are used to mensurate the temperature of the working fluid or vas. Degree centigrade: UsersAlY RaZaAppDataLocalMicrosoftWindowsTemporary Internet FilesContent.WordUntitled.png1.4.3-AdvantagesThe chief advantage of the tenseness burden cell is that it is extremely sensitive and stable. As it is a vibrating component wire detector and its end product is frequency so it is non affected by the alteration in the overseas telegram opposition and therefore long signal overseas telegrams are non jobs. The frequence of the vibrating wire is measured by either the portable read-out box or informations lumberman. So it can give more accurate readings. The end product signal scopes in the electromotive force from 0 to 5 Vs so there is no elaboration unit required and therefore the cost lessenings. The rated capacity of the tortuosity burden cell is from 10 kilograms to 15 kilograms. The truth of the tortuosity burden cells is A ±0.1 % The temperature ranges for the working or operation of the tortuosity burden cells is -20A °C to +80A °C. Such types of transducers have about zero impetus and have besides really low consequence of temperature on its truth.1.4.4-DisadvantagesThis type of burden cells can non be used for high temperature fluids to happen degree or weight of fluid incorporating column. This type of burden cells can non besides be used for high capacities or for big armored combat vehicles column or weight measurings. This type of burden cell is extremely affected by the high temperatures due to its sensitive nature of the detection wire.1.5-Pneumatic Load CellsThis is another type of burden cells which are usage to mensurate the weight in the industry and these are used for low capacity.1.5.1-Working PrincipleThis type of burden cells works on â€Å" the force-balance rule. †1.5.2-The Force-Balance PrincipleThe inertial force produced by a seismal land gesture shifts the mass from its original equilibrium place, and the alteration in place or speed of the mass is so interpreted into an electric signal. This rule is for low scope burden cells. For long scope burden cells the inertial force is balanced with an electrically generated force so that the mass moves every bit low as possible.1.5.3-Working of pneumatic burden cellThis sort of burden cells consist of a detection component which is exposed to the site or the vas of which force per unit area or lying unstable weight is to be measured. And in this sort of burden cell the force reassigning medium is air as comparison to the any other fluid in instance of hydraulic burden cell. When force is applied by the lying fluid on the feeling portion of the burden cell it transfers this force to the inside air and so this force is applied on the potentiometer which is placed in the wheat rock span. As the force is applied on the feeling portion of the burden cell the opposition of the variable opposition potentiometer alterations due to this force and therefore the possible equilibrium between the oppositions is disturbed and this shows the magnitude of the applied force on the feeling component by exposing it on the show unit. Figure pneumatic.gif Another technique which is largely used in such sort of burden cells is the use of the piezoelectric crystals. In this sort the detection component transportations applied force to the interior fluid ( air ) and it imparts this force on the crystal. And due to the application of the applied force on the crystal by agencies of air its construction gets disturbed and due to disturbance in the construction the possible across the crystal alterations and this alteration in the possible across the crystal is detected by the voltmeter and so this electromotive force is converted into weight of force units and displayed on the exposing unit. Most of the clip wheat rock span is used for this sort of burden cell and there is merely variable resistance largely used while other resistances in the wheat rock span are of fixed opposition.1.5.4-AdvantagesThey are largely used on smaller tons when safety and protection are of premier concern. They are better in truth as comparison to the hydraulic burden cells because there is no alteration in the denseness and truth of the fluid being used for the transportation of applied force. They besides preferred on the hydraulic burden cells because there is no usage of liquid in these sorts of burden cells. These types of burden cells are inherently explosion cogent evidence and insensitive to temperature fluctuations. As they contain no fluids so there is no job of taint of the procedure if the stop gets ruptured. Pneumatic burden cells are besides used to mensurate little weights that depend upon cleanliness and safety.1.5.5-DisadvantagesThe chief disadvantage of these types of burden cells is that they can non be used for high measure measuring. Although they are really resistive to the temperature effects but their truth even acquire disturbed at really high temperature.1.6-Hydraulic Load CellsThis is another type of burden cells which are used to mensurate the magnitude of the applied force and their transition to the electric signals and its digital show.1.6.1-Working PrincipleThis type of burden cells besides work on â€Å" the force-balance rule. † The difference between the pneumatic burden cell and hydraulic burden cell is merely the transferring medium. In instance of pneumatic burden cell the force reassigning medium is air while in hydraulic burden cells the force reassigning medium is largely liquid or incompressible oil which is besides known as break oil.1.6.2-Construction and workingHydraulic burden cell consists of a fluid which act as a force reassigning medium and a piezoelectric crystal which is usage to change over this applied force into possible difference and so there is an agreement for the transition of this possible difference in footings of weight or force per unit area. There is a stop which is usage to feel the force exerted from the external side and the whole shell in which this complete cell is enclosed. When the force per unit area or weight by the vas or column is applied on the stop of the burden cell it sense that force and so transportations this force to the fluid which is filled in the shell of this burden cell. Then this force is transferred to the piezoelectric crystal by the fluid or oil and this oil transfers this force by the Pascal ‘s jurisprudence. So when the force is transferred by the oil it disturbs the internal construction of the piezoelectric crystal and due to this alteration in the construction of the piezoelectric crystal a possible difference is generated across the piezoelectric crystal. This possible difference is detected by the electric sensor and electric signal is transferred to the show unit to expose the magnitude of the applied force, weight or force per unit area. Figure Hydraulic.gif1.6.3-AdvantagesThese are largely use to happen the weight of the stuff in the storage armored combat vehicles, bin or hopper. The end product given by these types of burden cells is additive and largely unaffected by the sum of the filling fluid ( oil ) or by its temperature. If the hydraulic burden cells have been decently installed and calibrated so truth is largely within 0.25 % full graduated table or better and this is acceptable for most procedure weighing applications. As these types of burden cells have no electrical constituents therefore it is ideal for usage in risky or caustic countries. For more accurate measuring, the weight of the armored combat vehicle should be obtained by turn uping a burden cell at different points and summing their end products.1.6.4-DisadvantagesOne disadvantage of this type of burden cell is that the elastomeric stop limits the maximal force that can be applied on the Piston or stop to about 1,000 psig. Electronic pari-mutuel machine is required in instance of acquiring more accurate reading by summing the readings of the single burden cells. Another disadvantage of hydraulic burden cell is that they are expensive and are complex to utilize.1.7-Shear Load CellsThis is another type of burden cells which is usage to mensurate the weight or the degree of the column incorporating fluid or some stuff.1.7.1-Working PrincipleThis type of burden cells works on the shear of the web. A web of an elastic stuff is inserted at some degree in the vas or storage armored combat vehicle and a shear emphasis exerted by the unstable column stretches the web harmonizing to the burden of the unstable column. Therefore by mensurating the shear emphasis the degree or weight of the fluid in a column can be measured.1.7.2-Construction and workingThis type of burden cells consists of a web and a frame which is movable and the web is fixed with this frame. There are strain gages which are straight connected with this web and step the weight or degree of the column by mensurating the shear emphasis exerted by the liquid nowadays in the column on the web. As the web is inserted in the liquid column, liquid exerts the force on this web as this web is stretchy and elastic so it gets stretched and this stretched province of the web is sensed by the strain gages. This web is inserted in the liquid column perpendicular to the axis of the column. Then strain gages transfers the mensural value of the shear emphasis exerted by the tallness of the liquid column to the electrical transducers which converts it into electrical signals and so transmits it to the show unit to expose the mensural value of the weight in footings of degree or force per unit area as we required. Figure1.7.3-AdvantagesShear burden cells are popular now for all type of mediums and for high capacities. Shear-web is non limited to merely beam constellations. Shear-web detection component is besides being used by high capacity BSP and USP in a more complex manner. Shear burden cell engineering is besides being used in rearward transducers. Shear tonss cells can readily be sealed and can be protected from the environmental effects.1.7.4-DisadvantagesShear burden cells have comparatively little sensitiveness at the burden point so can non be used for little graduated table measurings. Shear burden cells are expensive as comparison to the strain gages. Shear burden cells are delicate merely because of the web which is really delicate and can be easy damage due to overload fro few minutes even.

Antigone: Beliefs, Opinions, and Moral Views Essay

Antigone and Creon, from â€Å"Antigone† by Sophocles, encounter a philosophical war based on their moral views. A conflict arose when the principles that backed up their actions disagreed with each other. Antigone’s side of the conflict held a gods’ law is the way approach, as opposed to the â€Å"I am king† approach Creon chose to follow. The variation in the beliefs, opinions, and moral views of Antigone and Creon were constantly disputed through out the play. Antigone felt that Creon was disregarding the laws of gods through his law. After she was captured and brought to Creon, she told him, â€Å"Your edict, King was strong, but all your strength is weakness itself against the immortal unrecorded laws of God. They are not merely now: they were, and shall be, operative for ever, beyond man utterly.† Antigone’s opinion is one that supports the Gods and the laws of heaven. Her view is set by her belief that if someone is not given a proper burial, then that person would not be accepted into heaven. Antigone was a very religious person, and acceptance of her brother by the Gods was very important to her. She felt that â€Å"†¦I will bury him; and if I must die, I say that this crime is holy: I shall lie down with him in death, and I shall be as dear to him as he to me.† Creon’s order was personal to Antigone, as she saw his law as invading her family life as well as offensive to the Gods. In Antigone’s eyes, Creon betrayed the laws of the Gods by not allowing her to properly bury her brother, Polynices. She believed that the burial was a sacred ritual, and Creon did not have the authority to refuse Polynices his entitlement. Antigone’s strong belief towards the burial of her brother is what led her to her death by the hands of Creon. Since Creon was ruler, whatever he said was the law, and since Antigone broke his law, Creon was in a sense to blame, because if that law wasn’t put into effect then Antigone wouldn’t have hung herself. Nevertheless, she did not stop defending what she thought was proper. Right before her death, Antigone exclaimed, â€Å"†¦ you see me now, the last unhappy daughter of a line of kings, your kings, led away to death. You will remember what things I suffer and at what men’s hands, because I would not  transgress the laws of heaven.† She feels that Creon is abusing his power as king and dealing with her task on a personal level. Creon’s actions were based off of the fact that, â€Å"†¦ no ruler can expect complete loyalty from his subjects until he has been tested in office.† Polynices’ body left unburied is a symbol of Creon’s action to achieve the loyalty that he desired. â€Å"As long as I am King, no traitor is going to be honored with the loyal man.† Leaving the body unburied was done to show respect for Thebes, not in spite of the family. After all, how could the ruler of a kingdom honor a man who attempted to invade and conquer what is now his kingdom. This was far from the beliefs of Antigone. She believed that everyone deserved the right to have a proper burial, no matter what wrong doing that person may have done, and that the gods’ are the authorities that judge the afterlife. Due to this belief, Creon turned Antigone into his prisoner, and not the public’s. The general population actually supported Antigone, but though they were too scared to stand against Creon. Haimon knew of this and told his father, â€Å"Died so shameful a death for a generous act: ‘She covered her brother’s body. Is this indecent? She kept him from dogs and vultures. Is this a crime? Death? – She should have all the honor that we can give her!’ This is the way they talk out there in the city.† Creon was exercising complete domination of political power. By not allowing Antigone to perform her religious ceremony of burying her brother is interfering with religious affairs. This act denied Antigone of her religious freedom. Creon had to weigh each factor carefully, and had to decide between his morals and his beliefs. He was torn, trying to choose what was just. â€Å"†¦ Oh it is hard to give in! But it is worse to risk everything for stubborn pride.† The conflict of beliefs was what led to Antigone’s, Haimon’s, and Megareus’ death. Both sides were just, but Creon was forced to decide and determine right from wrong when there was no clear answer. In the end, the Chorus’ opinion was the determining factor and they convinced Creon to set Antigone free, but it was already too late. The conflict between the beliefs of Creon and Antigone are layered throughout the play. Both have logical arguments, but neither dominates the other. Antigone is motivated by her strong religious feelings, while Creon is trying to be lawful and do what’s right for his kingdom. Neither won this battle, as Antigone took her life, the lives of Creon’s wife and son followed, leaving Creon with nothing but his precious kingdom.

Arthur Millers play Essay

Arthur Millers play ‘The Crucible’ is, on the surface, a play about a real life historical event that took place in the small American town of Salem in 1692. A mass hysteria gripped the town because of accusations of witchcraft and compacting with the devil. This led to many innocent people being hanged. However, some people believe that if you look deeper into the play you can see clear parallels with 1692 Salem and 1950’s America. After the end of the Second World War most of Europe was devastated and left trying to recover. This left the USA and the USSR as the two dominant superpowers, both of these heavily armed nations were extremely scared of the other attacking them and so came an arms race to try to beat the other side. Diplomatic relations between the two powers broke down and widespread fear of communism took over the USA. So began the ‘Cold War’. Senator Joseph McCarthy set up the House Un-American Committee to root out communists and their sympathisers. This included anyone who had remotely left-wing views. Many actors, writers and musicians were brought before the committee including Miller himself. If you remember a crucible is a dish used to heat out the impurities from metals, you can see how it relates to Proctor in court being ‘heated’ to provide names and confessions. This is much the same as what happened to Miller who was also asked to name names (but refused). To answer the question it has to be remembered that Miller intended that the play be performed on stage and not read like a book. He uses stage directions to convey to the audience some of the feelings characters are experiencing. On page 108 stage directions for Proctor say â€Å"With great force of will, but not quite looking at her†. The shows the audience that Proctor still cannot forgive himself for his affair with Abigail. It also shows the conflict between Proctor and Elizabeth and also Proctor and Abigail. Proctor also has a conflict with Parris, who he correctly believes is an incompetent fool. In addition to this he also has conflict he also a conflict with all the girls because he knows they are faking the whole thing. Miller shows this by having Proctor go to court to try and prove the girls liars. He brings Mary Warren into Court saying, â€Å"She never saw no spirits†. He also has conflicts with judges Haythorne and Danforth. On page 113 he says â€Å"I speak my own sins, I cannot judge another. (Crying out with hatred)† The stage directions for this quote clearly shows this conflict. These conflicts are all of one particular type, conflicts with other people, except for the conflicts with Judges Haythorne and Danforth who could also represent Proctors conflicts with Authority.  Reverend Hale has a conflict with Proctor because he believes that Proctor should sign the confession to live and not die for his pride. At one point he shows his anger at Proctors decision to tear up his confession says â€Å"Man, you will hang! You cannot!.  A lot of characters especially Proctor have conflicts with authority. Proctor has a huge conflict with the courts and also the church, although the two are very close together. This is where Miller uses him to explore his own conflict with McCarthyism and his own experiences before the House Un-American Committee. On page 114 stage directions for Proctor read â€Å"Proctor has finished signing when Danforth reaches for the paper. But Proctor snatches it up and now a wild terror is rising in him, and a boundless anger† this shows very much how much Proctor hates the courts and could also show us something of Millers feelings towards McCarthyism. This is because both Proctor and Miller know that the courts/government are almost trying to bribe people into giving the names of others even if the others are innocent people that are being named to get them out of trouble or being named for some kind of revenge purpose. To add to his long list of conflicts Proctor also has a conflict within himself about whether or now he should sign the confession and name people to save his life or to protect others and his honour and die. Miller also faced this (although he was only threatened with jail not death) but like Proctor he refused to name people and escaped without severe punishment.  Elizabeth Proctor also has conflicts within herself as to whether or not to help John Proctor in his decision to sign the paper or not. In the end she does not help him and he must do it himself. This may show how alone you could feel when being questioned about your â€Å"Un-American Activities† in 1950’s/60’s America. In the end of the play Proctor is hung for not confessing or naming names. This ending solves many of the conflicts in the play. It solves all Proctors conflicts with people and authority and also other people conflicts with him. However it could spark of new conflicts within people such as the girls who faked the whole thing and must be wondering whether they should have said something before people were killed or whether to say something now. I think Miller is using his characters to show us different conflicts in society and the problems with people and how they can do things they ordinarily wouldn’t to gain an advantage or to escape trouble. He also uses the conflicts to show problems with high authority and how they could collapse if they were revealed to be wrong about serious things like the witch trials. I think Miller is trying to tell us something we should all probably learn from.

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Constitutional & Administrative Law - Essay Example he first being that the parliament may legislate upon any subject-matter; secondly that Parliament could not be restricted by a predecessor not restrict the powers of a future Parliament; and finally the validity of Acts of Parliament cannot be challenged. Under the legal theory Parliament is entitled to pass law on anything once it has been passed by the House of Commons, House of Lords and receives Royal Assent and such would be held to be legally valid. The limits that have been listed down are those that have been laid down by the democratic process. Thus theoretically the powers of the parliament are absolute and so an Act can extend beyond the territory of the United Kingdom. Furthermore, Parliament can legislate with the Act having retrospective effect. As far as international law is concerned it cannot have effect unless implemented by the Parliament by introduction of an Act. As far as Parliament being bound or being able to bind its successor is concerned importance has been placed on the Act of Union with Scotland 1707, whereby it was suggested that intention of the Act was that it cannot be repealed; however, it is important to mention that there have been amendments that have been made. In Attorney General for New South Wales v. Trethowan2 the Privy Council found the Parliament to be bound by a previous Act while citing the reason that the earlier Act had to be repealed first and so if it was not repealed then the Parliament was bound by it. As far as the new view of sovereignty is concerned Sir Ivor Jennings and Professors Heuston, Marshall, Mitchell and de Smith have stated that Parliament can bind its successor, by redefining itself or by setting out ‘ manner and form’ provisions which need to be followed. A recent example in respect of the procedural requirements is that of Northern Ireland Act 1998 whereby it stated that the Northern Ireland would remain a part of United Kingdom unless done to the contrary by means of a referendum by the

Self-medication Hypothesis Essay Example for Free

Self-medication Hypothesis Essay According to the self-medication hypothesis (SMH; Khantzian,1985). The individuals choice of a particular drug is not accidental or coincidental, but instead, a result of the individual’s psychological condition, as the drug of choice provides relief to the user specific to his or her condition. Specifically, addiction is hypothesized to function as a compensatory means to modulate effects and treat distressful psychological states, whereby individuals choose the drug that will most appropriately manage their specific type of psychiatric distress and help them achieve emotional stability. Alcohol use may relieve anxiety, for this reason alcohol consumption is reinforcing particularly when consumed in stressful condition. Drinking can improve mood and social adjustments, remove stress and burdens. As stated to the SMH the choice of a particular drug is a result of the individual’s psychological condition, socially anxious people might be expected to use alcohol as a coping action in try at self-medication and to manage their anxiety. Based on the Drive Reduction Theory (Clark Hull, 1943) the reduction of drives is the primary force behind motivation. In his theory, Hull used the term drive to refer to the state of tension or arousal caused by biological or physiological needs. A drive creates an unpleasant state; a tension that needs to be reduced. In order to reduce this state of tension, humans and animals seek out ways to fulfil these biological needs. Drive theory is based on the principle that organisms are born with certain psychological needs and that a negative state of tension is created when these needs are not satisfied. Drinking alcohol is a way for socially anxious people to reduce their anxiety, so every time they will engage to a social situation they will use alcohol for conditioning and strengthening. As Hull suggested, humans and animals will then repeat any behaviour that reduces their drives. Based on Decision theory every action at least implicitly represents a decision under uncertainty: in a state of partial knowledge, something has to be done, even if that something turns out to be nothing. Even if you dont know how you make decisions, decisions do get made, and so there has to be some underlying mechanism. The said theory states how people with social anxiety decide. They decide to use alcohol to reduce their anxiety, to handle with the symptoms or to try to get away from it. Since alcohol has a soothing effect and produces a sense of thrill and decreased shyness apparently providing relief from anxiety.

Reducing HIV Stigma Among Nursing Students

Reducing HIV Stigma Among Nursing Students 1 The journal article being critiqued is a study of HIV stigma and a study’s intervention at reducing that stigma among nursing students. First, stigma is introduced, the type of stigma’s seen with HIV, and then how those are interpreted in nursing practice. The purpose of the study was to reduce HIV stigma in nursing students through a dynamic course given at a nursing school. The article will be reviewed, analyzed, and critiqued in its significance as a research source and implementation value. A study was carried out by the University of California in India, at a nursing school in a city where HIV prevalence was high. This study consisted of a curriculum, and 91 nursing students. The class was focused on educating and reducing different stigma-influencing measures of HIV. The sample received a pre and posttest that served as the main set of data for how the class influenced the student’s HIV stigma. Statistics was used to evaluate student response data in its measures of standard deviation and confidence intervals. These measures helped the study in deciding whether student answers were significant, or how effective their class was on reducing HIV stigma. An HIV stigma is something that can alters one’s view of a person with HIV that is based on some cultural or social belief. The study believes that stigma can devalue or interfere with care for a person with HIV. This commonly effects people who are drug users, sex workers, or of the male homosexual population. It not only affects a nurse’s care, but also the patient’s motivation to seek care. The study states, â€Å"HIV stigma is considered to be among the greatest impediments to effectively combating the global HIV epi- demic.† There is instrumental and symbolic stigma, which includes misconceptions about transmission and attitudes or beliefs towards the previously stated populations commonly believed to have HIV. The method of this study was at a nursing school in India, St John’s College of Nursing. Second year, English speaking students were the sample group. They were given information about what the study was going to test and signed informed consent to participate. The control group was 46 people, and the intervention group was 45 people. The course was focused on the two types of stigmas previously mentioned and offered on session on instrumental stigma, which included knowledge, fears, epidemiology, transmission, prevention and proper use of PPE. The second session was on symbolic stigma and had a speaker come and talk about their experience with HIV and HIV stigmas. The control received no intervention. A questionnaire was given before and after the interventions that assessed student’s symbolic and instrumental stigmas. They were asked questions like their gender and age, prior care for a person with HIV, their attitudes, misconceptions, fears, discrimination, and so fo rth. The topics of the questionnaires tested demographics, experience with persons with HIV, knowledge of HIV, endorsement of coercive measures, worry about HIV infections, blame, and intent to discriminate. This is included true or false, with different right and wrong misconceptions or truths about HIV. They were tested on whether they agreed with certain statements like mandatory testing, right to refuse an HIV patient, to marry, have children, etc. One question asked if the student blamed people with HIV for their disease or thought they deserved it. There were multiple-choice questions about medication administration and blood draws and precautions to take that tested the student’s intent to discriminate. Each section had a few questions that was intended to test the students aptitude in that subject area. All participants were female and between 18 and 29 years old. Results were found to be significant. Post-intervention found many changes from the baseline that showed a reduction in stigma based on previous definitions. There was a lower percentage of misconceptions in the intervention group compared to the control group. Participants who had preexisting discrimination among people with HIV lowered with a question regarding medication administration, but did not lower with regard to drawing blood. There were a slightly lower number of people who worried about transmission of HIV but were not statistically significant when compared to the control group. On average about 95% of students believed the session was helpful and would change their care towards a person with HIV. About 40% of students were embarrassed to reveal their opinions about it. The questionnaire taken before the intervention showed that the students had a fairly high HIV stigma. Compared the post questionnaire, control group, and preceding results, a conclusion that the course â€Å"showed promise† in lowering stigma of people with HIV was perceived. The questionnaire showed that students had high levels of â€Å"intent to discriminate while performing nursing duties.† In the study it says this may be because of lack of experience. Also students said that people with HIV were blamed for their disease if it was through drugs or sex and believed mandatory testing of sex workers and male homosexuals was called for. One of the biggest findings of this questionnaire was that there was seen to be a lack of knowledge among nursing students in transmission of HIV, blame of persons with HIV, discrimination in a professional workplace, and calling of coercive measures. This shows high stigma levels, which were akin to high discrimination levels of peopl e with HIV. After the course however, it was shown to be effective in giving students more knowledge base for HIV stigma across many dynamics. The post questionnaire showed fewer misconceptions, less blame, and decreased discrimination. Not all data deemed to be statistically significant, but the data that was significant still deemed the course in reducing HIV held promise. It might be more effective with a larger sample that also included male nurses, varying ages, and varying schools. It is significant that this study used a â€Å"convenience sample† of people that were readily available and in a high prevalence HIV area. Taking the study to various states, cities, and people of different cultural and moral values would make this study more significant in it’s actual effectiveness in reducing HIV stigma. Future continuation of this study should look at various population content and high numbers of people, mainly. All measures used to define stigmas, assess stigma levels, and test prejudice was based on a previously developed theoretical model of HIV that had been formulated in India. The definitions and guidelines of the curriculum seemed to be well defined and showed a good possibility of being standardized for larger sample size testing. They were also easy to understand and interpret. The questionnaire was a successful evaluation too l for this study (with 29 questions) and was well defined in the article. It might also benefit this study to try different methods of evaluation other than only using a questionnaire survey technique. It may even be interesting to compare the nursing students results with already registered nurses, experienced nurses, doctors, UAP’s, and patients/civilians. This study is very important to nursing care today. HIV stigma is prevalent and something that is seen daily. Marginalized groups such as homosexual populations, female sex workers, and drug users should not be stigmatized from the moment they enter a hospital or become a patient, that is something they do experience as not only a marginalized group, but also the select few with HIV. Nurses are the basis of these patients’ care and need to be able to give care without bias or discrimination. This requires evaluating ones own beliefs of this stigma. A course that helps nurses through this process while also giving them a dynamic educational and experiential background of stigma’s, transmission, and persons with HIV would be extremely helpful to that patients care. Anything that can help nurses become better, give more effective care, and be more sensitive to others cultures, beliefs and illness is helpful to the medical field, and more importantly, helpful to the patient s healing and disease process. Personally, I believe that people with HIV are stigmatized well beyond due cause. Yes they have an incurable disease, and it can be transmitted through blood, which we deal with a lot as a nurse. But we still need to be professional and give proper care. A person with HIV is something that has been very popular to stigmatize, especially in our social and cultural society in the United States. Even I realized I hold some of these beliefs as I read this study. It is important as a professional, and as a nurse, to make sure we hold everyone to the same standard of care and give continuity in our nursing process. If this course was available to me it is definitely something I would be interested in taking. It can only help me to become a more effective and sensitive nurse to a patient with HIV and it is something that could easily be added into hospital orientation. It would be great to make it available to all staff and be more knowledgeable and less discriminatory against those with HI V and the marginalized population we target when we have an HIV stigma. This study is really just the tip of the iceberg on the subject of reducing HIV stigma, but I feel it’s the step in the right direction and could be vital in finding a way to resolve prejudices against HIV. Citation List 1. Shah, S., Srinivasan, K., Perumpil, S., Ekstrand, M. (2014). Reducing HIV Stigma Among Nursing Students: A Brief Intervention. Western Journal of Nursing Research, 36(10), 1323-1337. Retrieved October 19, 2014, from Sagepub.

Model for Predicting Fatigue Life of Nanomaterials

Model for Predicting Fatigue Life of Nanomaterials Introduction In the past, the primary function of micro-systems packaging was to provide input/output (I/O) connections to and from integrated circuits (ICs) and to provide interconnection between the components on the system board level while physically supporting the electronic device and protecting the assembly from the environment. In order to increase the functionality and the miniaturization of the current electronic devices, these IC devices have not only incorporated more transistors but have also included more active and passive components on an individual chip. This has resulted in the emerging trend of a new convergent system[1] Currently, there are three main approaches to achieving these convergent systems, namely the system-on-chip (SOC), system-in-package (SIP) and system on package (SOP). SOC seeks to integrate numerous system functions on one silicon chip. However, this approach has numerous fundamental and economical limitations which include high fabrication costs and integration limits on wireless communications, which due to inherent losses of silicon and size restriction. SIP is a 3-D packaging approach, where vertical stacking of multi-chip modules is employed. Since all of the ICs in the stack are still limited to CMOS IC processing, the fundamental integration limitation of the SOC still remains. SOP on the other hand, seeks to achieve a highly integrated microminiaturized system on the package using silicon for transistor integration and package for RF, digital and optical integration[1] IC packaging is one of the key enabling technologies for microprocessor performance. As performance increases, technical challenges increase in the areas of power delivery, heat removal, I/O density and thermo-mechanical reliability. These are the most difficult challenges for improving performance and increasing integration, along with decreasing manufacturing cost. Chip-to-package interconnections in microsystems packages serve as electrical interconnections but often fail by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that integrated chip (IC) packages will have interconnections with I/O pitch of 90 nm by the year 2018 [2]. Lead-based solder materials have been used for interconnections in flip chip technology and the surface mount technology for many decades. The traditional lead-based and lead-free solder bumps will not satisfy the thermal mechanical requirement of these fine pitches interconnects. These electronic packages, even under normal operating conditions, can reach a temperature as high as 150C. Due to differences in the coefficient of thermal expansion of the materials in an IC package, the packages will experience significant thermal strains due to the mismatch, which in turn will cause lead and lead-free solder interconnections to fail prematurely. Aggarwal et al [3] had modeled the stress experienced by chip to package interconnect. In his work, he developed interconnects with a height of 15 to 50 micrometre on different substrate using classic beam theory. Figure 1 shows the schematic of his model and a summary of some of his results. Although compliant intrerconect could reduces the stress experienced by the interconnect, it is still in sufficient. Chng et al. [4] performed a parametric study on the fatigue life of a solder column for a pitch of 100micrometre using a macro-micro approach. In her work, she developed models of a solder column/bump with a pad size of 50micrometre and heights of 50 micrometre to 200 micrometre. Table I shows a summary of some of her results. Table 1.1: Fatigue life estimation of solder column chip thickness (micrometre) 250 640 640 640 board CTE (ppm/K) 18 18 10 5 solder column height (micrometre) Fatigue life estimation/cycle) 50 81 N.A 171 3237 100 150 27 276 3124 150 134 31 518 4405 200 74 38 273 5772 It can be seen from Table 1.1 that the fatigue lives of all solder columns are extremely short. Apart from the 5ppm/K board where there is excellent CTE matching, the largest fatigue life of the solder column is only about 518 cycles. As expected, the fatigue life increases significantly when the board CTE decreases from 18ppm/K to 10ppm/K and as the height increases from 50micrometre to 200micrometre.This is mainly due to the large strain induced by the thermal mismatch as shown in Figure 1.2. The maximum inelastic principal strain was about 0.16 which exceeds the maximum strain that the material can support. Although the fatigue life of the chip to package interconnection can be increases by increasing the interconnects height, it will not be able to meet the high frequency electrical requirements of the future IC where they need to be operating at a high frequencies of 10-20 GHz and a signal bandwidth of 20 Gbps, By definition, nanocrystalline materials are materials that have grain size less than 100nm and these materials are not new since nanocrystalline materials have been observed in several naturally-occurring specimens including seashells, bone, and tooth enamel [5, 6]. However, the nanocrystalline materials have been attracting a lot of research interest due to its superior mechanical and electrical properties as compared to the coarse-grained counterpart. For example, the nano-crystalline copper has about 6 times the strength of bulk copper [7]. Furthermore, the improvement in the mechanical properties due to the reduction in grain size has been well-documented. Increase in strength due to the reduction in grain-size is predicted by the Hall-Petch relationship which has also been confirmed numerically by Swygenhoven et al [8] and was first demonstrated experimentally by Weertman [9]. The implantation of nanocrystalline copper as interconnect materials seems to be feasible from the processing viewpoint too. Copper has been used as interconnects materials since 1989 whereas nano-copper has also been widely processed using electroplating and other severe plastic deformation techniques in the past few years. For instance, Lu et al. [10] have reported electroplating of nano-copper with grain size less than 100 nm and electrical conductivity comparable to microcrystalline copper. Furthermore, Aggarwal et al [11] have demonstrated the feasibility of using electrolytic plating processes to deposit nanocrystalline nickel as a back-end wafer compatible process. However, there are certain challenges regarding implantation of nanocrystalline copper as interconnects materials. As discussed above, nanocrystalline copper have a high potential of being used as the next generation interconnect for electronic packaging. However, it is vital to understand their material properties, deformation mechanisms and microstructures stability. Although the increase in strength due to the Hall-Petch relationship which has also been confirmed numerically and experimentally by Weertman [9], the improvement in the fatigue properties is not well documented and no model has been established to predict/characterize these nano materials in interconnection application; conflicting results regarding the fatigue properties have also been reported. Kumar et al [12] reported that for nano-crystalline and ultra-fine crystalline Ni, although there is an increase in tensile stress range and the endurance limit, the crack growth rate also increases. However, Bansal et al. [7] reported that with decreasing grain size, the tensile stress range increases but the crack growth rate decreases substantially at the same cyclic stress intensity range. Thus, nanostructured materials can potentially provide a solution for the reliability of low pitch interconnections. However, the fatigue resistance of nanostructured interconnections needs to be further investigated. Since grain boundaries in polycrystalline material increases the total energy of the system as compare to perfect single crystal, it will resulted in a driving force to reduce the overall grain boundary area by increasing the average grain size. In the case of nanocrystalline materials which have a high volume fraction of grain boundaries, there is a huge driving force for grain to growth and this presented a presents a significant obstacle to the processing and use of nanocrystalline copper for interconnect applications. Millet et al [13] have shown, though a series of systematic molecular dynamics simulations, grain growth in bulk nanocrystalline copper during annealing at constant temperature of 800K can be impeded with dopants segregated in the grain boundaries regions. However, it has been observed that stress can trigger grain growth in nanocrystalline materials [14] and there is no literature available on impeding stress assisted grain growth. There is an impending need to investigate the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth Dissertation Objectives The goal of present project is to develop a model for the fatigue resistance of nano-materials that have been shown to have superior fatigue resistance. Accordingly, the following research objectives are proposed. Develops a model for predicting fatigue life of nanostructured chip-to-package copper interconnections Develops a fundamental understanding on the fatigue behavior of nanocrystalline copper for interconnect application Addresses the issue on the stability of nanocrystalline materials undergoing cyclic loading Overview of the Thesis The thesis is organized so that past research on nanocrystalline materials forms the basis of the understanding and new knowledge discovered in this research. Chapter 2 reviews much of the pertinent literature regarding nanocrystalline materials, including synthesis, deformation mechanisms, and grain growth. Chapter 3 describes a detailed overview of the technical aspects of the molecular dynamics simulation method including inter-atomic potentials, time integration algorithms, the NVT NPT, and NEPT ensembles, as well as periodic boundary conditions and neighbor lists. Include in this chapter is the algorithms for creating nanocrystalline materials used in this dissertations.. Chapter 4 describes the simulation procedure designed to investigate and develop the long crack growth analysis. The results of the long crack growth analysis will be presented at the end of Chapter 4. Chapter 5 presents the result and discussion on mechanical behavior of single and nanocrystalline copper subjected to monotonic and cyclic loading whereas Chapter 6 presents the result and discussion on the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth. Finally, conclusions and recommendations for future work are presented in Chapter 5. Chapter 2 This chapter offers an expanded summary of the literature published with regards to the fabrication methods, characterization, and properties of nanocrystalline materials in addition to a description of existing interconnect technology. 2.1 Off-Chip Interconnect Technologies Chip-to-package interconnections in microsystems packages serve as electrical interconnections but they will often failed by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that interconnections of integrated chip (IC) packages will have a I/O pitch of 90 nm by the year 2018 [2]. The International Technology Roadmap for Semiconductors (ITRS) roadmap is a roadmap that semiconductor industry closely follows closely and its projects the need for several technology generations. The package must be capable of meeting these projections in order for it to be successful. This section reviews some of the current interconnect technology. Wire bonding [15] as shown in Figure 2.1, is generally considered as one of the most simple, cost-effective and flexible interconnect technology. The devices on the silicon die are (gold or aluminum) wire bonded to electrically connect from the chip to the wire bond pads on the periphery. However, the disadvantages of wire bonding are the slow rate, large pitch and long interconnect length and hence this will not be suitable for high I/O application. Instead of wires in the wire bonding, tape automated bonding (TAB) is an interconnect technology using a prefabricated perforated polyimide film, with copper leads between chip and substrate. The advantage of this technology is the high throughput and the high lead count. However, it is limited by the high initial costs for tooling. An alternative to peripheral interconnect technology is the area-array solution, as shown in Figure 2.3, that access the unused area by using the area under the chip. In area-array packaging, the chip has an array of solder bumps that are joined to a substrate. Under-fill is then fills the gap between the chip and substrate to enhance mechanical adhesion. This technology gives the highest packaging density methods and best electrical characteristics of all the avaiable interconnection technology. However, not only is its initial cost is high, it requires a very demanding technology to establish and operate. With the need for higher I/O density, compliant interconnects have been developed to satisfy the mechanical requirements of high performance micron sized interconnects. The basic idea is to reduce shear stress experienced by the interconnects through increasing their height or decreasing of its shear modulus (i.e. increases in their compliant) and hence the name compliant interconnects. Some of recent research in compliant interconnects include Tesseras Wide Area Vertical Expansion, Form Factors Wire on Wafer and Georgia Institute of Technologys Helix interconnects [17-19] as shown in Figure 2.4. Although compliant interconnects can solve the problem of mechanical reliability issue, they are done at the expense of the electrical performance. Since there is a need to reduce the packages parasitic through a decrease line delays, there is a need to minimize the electrical connection length in order to increase the system working frequency. Hence, compliant interconnect may not meet the high electrical frequency requirements of future devices. Figure 2.4: (a) Wide Area Vertical Expansion, (b) Wire on Wafer and (c) G-Helix [17-19] Lead and lead-free solders typically fail mechanical when scaled down to less than to a pitch of 100 mm. Compliant interconnections, on the other hand, do not meet the high frequency electrical requirements. The Microsystems Packaging Research Center at Georgia institute of Technology had demonstrated the feasibility of using re-workable nanostructure interconnections. Aggarwal et al [20] had show that nanostructured nickel interconnections, through a Flip Chip test vehicle, was able to improve the mechanical reliability while maintaining the shortest electrical connection length. However, the main disadvantages of this method was the significant signal loss at high frequency signal of nanocrystalline nickel [21]. As discussed above, nanostructure interconnects technology is the most promising interconnect technology to best meet the stringent mechanical and electrical requirement of next generation devices. However, there is a need of an alternate materials and a sensible choice of materials in this case would be nanocrystalline copper for its high strength material with superior electrical conductivity. Hence, it would be beneficial to use nanocrystalline-copper as material for the nanostructure interconnects. Due to the tendency for the grain to grow, there is a need to stabilize the grain growth in nanocrystalline copper before using it could be considered as a potential candidate for nanostructure interconnect. 2.2 Nanocrystalline material Nanocrystalline materials are polycrystalline materials with an average grain size of less than 100 nm [22]. Over the past decade , new nanocrystalline or nanostructured materials with key microstructural length scales on the order of a few tens of nanometers has been gaining a lot of interest in the material science research society. This is mainly due to its unique and superior properties, as compared to their microcrystalline counterparts which includes increased strength [22] and wear resistance [23]. These unique properties are due to the large volume fraction of atoms at or near the grain boundaries. As a result, these materials have unique properties that are representative of both the grain boundary surface characteristics and the bulk. Recent advances in synthesis and processing methodology for producing nanocrystalline materials such as inert gas condensation [24], mechanical milling [25, 26], electro-deposition [27], and severe plastic deformation [28] have made it possible to produce sufficient nanocrystalline materials for small scale application. 2.2.1 Synthesis Inert gas condensation, the first method used to synthesis bulk nanocrystalline [29], consists of evaporating a metal inside a high-vacuum chamber and then backfilling the chamber with inert gas [30]. These evaporated metal atoms would then collide with the gas atoms, causing them to lose kinetic energy and condenses into powder of small nano-crystals. These powders are then compacted under high pressure and vacuum into nearly fully dense nanocrystalline solids. The grain size distribution obtained from this method is usually very narrow. However, the major draws back of this method are its high porosity levels and imperfection bonding. Grain coarsening also occurs due to the high temperature during the compaction stage [31]. Mechanical milling consists of heavy cyclic deformation in powders until the final composition of the powders corresponds to a certain percentages of the respective initial constituents [25, 26]. A wide grain size distribution is obtained by this method. This technique is a popular method to prepare nanocrystalline materials because of its applicability to any material and simplicity. However, their main drawback includes contamination and grain coarsening during the consolidation stage. Electro-deposition consists of using electrical current to reduce cations of a desired material from a electrolyte solution and coating a conductive object on the substrate. Electro-deposition has many advantages over processing techniques and this includes its applicability to a wide variety of materials, low initial capital investment requirements and porosity-free finished products without a need for consolidation processing [27]. Furthermore, Shen et al. [32] and Lu et al.[33] had recently show that the right electro-deposition condition can produce a highly twinned structure which leads to enhanced ductility. The main drawback of this method is it is the difficulty to achieve high purity. Severe plastic deformation, such as high-pressure torsion, equal channel angular extrusion (ECAE), continuous confined shear straining and accumulative roll-bonding, uses extreme plastic straining to produce nanocrystalline materials by mechanisms such as grain fragmentation, dynamic recovery, and geometric re-crystallization [34]. It is the only technology that transformed conventional macro-grained metals directly into nanocrystalline materials without the need of potentially hazardous nano-sized powders. This is achieved by introducing very high shear deformations into the material under superimposed hydrostatic pressure. Two of the most commonly used methods are high-pressure torsion and ECAE [35]. In the study of the effect of ECAE on the microstructure of nanocrystalline copper, Dalla Torre et al [36] observed that the grains become more equi-axial and randomly orientation as the number of passes increases, as shown in Figure 2.5 Figure 2.5: Microstructure of ECAE copper subjected to (a) 1 passes (b) 2 passes (c) 4 passes (d) 8 passes (e) 12 passes and (f) 16 passes [36] 2.2.2 Mechanical Behavior of nanocrystalline materials Due to the small grain size and high volume fraction of grain boundaries, nanocrystalline materials exhibit significantly different properties and behavior as compared to their microcrystalline counterpart. The structure and mechanical behavior of nanocrystalline materials has been the subject of a lot of researchers interests both experimentally [37-43] and theoretically [44-50]. This section reviews the principal mechanical properties and behavior of nanocrystalline materials. 2.2.2.1 Strength and ductility Recent studies of nanocrystalline metals have shown that there is a five to ten fold increases in the strength and hardness as compared to their microcrystalline state [7, 36, 37, 51, 52]. This increase in the strength is due to the presence of grain boundaries impeding the nucleation and movement of dislocations. Since decreasing grain boundary size increases the number of barrier and the amount of applied stress necessary to move a dislocation across a grain boundary, this resulted in a much higher yield strength. The inverse relationship between grain size and strength is characterized by the Hall-Petch relationship [53, 54] as shown in equation (2.1). Eq (2.1) In equation (2.1), s is the mechanical strength, k is a material constant and d is the average grain size. Hence, nanocrystalline materials are expected to exhibit higher strength as compared to their microcrystalline counterpart. Figure 2.6 and Figure 2.7 show the summary of hardness and yield strength from tensile test that are reported in the literature. Indeed, hardness and yield strength of copper with a grain size of 10nm (3GPa) can be one order higher than their microcrystalline counterpart. To the larger specimens. Derivation from Hall-Petch relationship begins as the grain size approaches 30nm where the stresses needed to activate the dislocation multiplication via Frank-Read sources within the grains are too high and the plastic deformation is instead accommodated by grain boundaries sliding and migration.[12]. Furthermore, as the grain size reduces, the volume fraction of the grain boundaries and the triple points increases. Material properties will be more representative of the grain boundary activity [64] and this will resulting the strength to be inversely proportional to grain size instead of square roots of the grain size as predicted by Hall Petch relation [65]. Further reduction in the grain size will result in grain boundaries processes controlling the plastic deformation and reverse Hall-Petch effect, where the materials soften, will take place. Although sample defects had been account for the earlier experimental observation of reverse Hall-Petch effect[24], Swygenhoven et al [66] and Schiotz et al [47], using molecular simulation, was able to showed that nanocrystalline copper had the highest strength (about 2.3GPa ) at a grain size of 8nm and 10-15nm respectively. Conrad et al [67] pointed out that below this critical grain size, the mechanisms shifted to grain boundary-mediated from dislocation-mediated plasticity and this causes the material to become dependent on strain rate, temperature, Taylor orientation factor and presence of the type of dislocation. The yield stress of nanocrystalline copper was highly sensitive to strain rate even though it is a fcc materials. The strain rate sensitivity, m, in equation 2.2 a engineering parameter which measured the dependency of the strain rate and Figure 2.8 shows a summary of m as a function of grain size for copper specimen in the literature [51, 68-70]. Due to high localized dislocation activities at the grain boundaries which results in enhanced strain rate sensitivities in nanocrystalline materials, m increases drastically when the grain size is below 0.1 mm as shown in Figure 2.8. (2.2) Room temperature strain rate sensitivity was found to dependent on dislocation activities and grain boundaries diffusion [52, 71, 72]. Due to the negligible lattice diffusion at room temperature, the rate limiting process for microcrystalline copper was the gliding dislocation to cutting through forest dislocation, resulting in low strain rate sensitivities. However, due to the increasing presence of obstacles such as grain boundaries for nanocrystalline materials, the rate limiting process for smaller grain size was the interaction of dislocation and the grain boundaries, which is strain rate and temperature dependence. By considering the length scale of the dislocation and grain boundaries interaction, Cheng et al [52] proposed the following model for strain rate sensitivities . (2.3) z is the distance swept by the dislocation during activation, r is the dislocation density and a, a and b are the proportional factors. With this model, they will be able to predict higher strain rate sensitivities for nanocrystalline material produced by severe plastic deformation as compared to other technique. Since the twin boundaries in nanocrystalline or ultra fine grain copper served as a barriers for dislocation motion and nucleation which led to highly localized dislocations near the twin boundaries, the strain rate sensitivity of copper with high density of coherent twin boundaries was found to be higher than those without any twin boundaries [33]. Lastly, the increase enhanced strain rate sensitivity in nanocrystalline copper had been credited for it increases in strength and ductility. For example, Valiev et al [60] credited the enhanced strain rate sensitivity of 0.16 for the high ductility. In addition to a strong dependency on the strain rate, strength in nanocrystalline materials was also highly dependent on the temperature. Wang et al [73] observed that the yield strength for ultra fine grain copper with a grain size of 300nm increases from approximately 370MPa to 500MPa when the temperature reduces from room temperature to 77k. The authors attributed this increase in yield strength due to the absence of additional thermal deformation processes at 77k. This is consistent with Huang et al [74] observation where the temperature dependence of nanocrystalline copper with an increase in hardness of nanocrystalline copper with lowering the temperature is noted Ductility is another important characteristic of nanocrystalline materials. In microcrystalline materials, a reduction in grain size will increase the ductility due to the presence of grain boundaries acting as effective barriers to the propagation of micro-cracks[75]. However, nanocrystalline copper showed a lower strain to failure than that of their microcrystalline counterparts and this lacks in ductility was attributed to the presence of processing defects [76]. Recent advanced in processing of nanocrystalline materials offer materials with fairly good ductility in additional to ultra-high strength. Lu et al [10] reported that nanocrystalline copper with minimal flaw produced via electro-deposition had an elongation to fracture of 30%. Furthermore, Youssef et al [77] observed a 15.5% elongation to failure for defect free nanocrystalline copper produced via mechanical milling. Hence, it was possible for nanocrystalline copper to be both strong and ductile if the processing artifacts are minimized. The failure are usually consists of dimples several time larger than their grain size was normally found on the failure morphology of nanocrystalline materials and Kumar et al [78] presented the following model for initiation and hence the eventual failure of nanocrystalline materials. Furthermore, the presence of shear region was found to be due to shear localization since the ratio of strain hardening rate to prevailing stress was usually small [79, 80]. Figure 2.9: Schematic illustration of fracture in nanocrystalline material postulated by Kumar et al [78] 2.2.2.2 Creeps Nanocrystalline materials are expected to creep during room temperature. This is because Due to the higher fraction of grain boundaries and triple junctions, self diffusivity of nanocrystalline material had been shown to increase by an order of three as compared to microcrystalline copper [81]. Since creep behavior was dependent on grain size and diffusivity, with creep rate increases with an increase in diffusivity or a decrease in grain size, the creep temperature for nanocrystalline copper was known to be a small fraction of melting temperature (about 0.22 of its melting points). Furthermore, since creep had always been cited as one of the reason for grain size softening in nanocrystalline materials, creeps were other important mechanical properties of nanocrystalline materials that had been gaining a lot of researchers attention. Due to the high volume fraction of grain boundaries and enhanced diffusivity rate Model for Predicting Fatigue Life of Nanomaterials Model for Predicting Fatigue Life of Nanomaterials Introduction In the past, the primary function of micro-systems packaging was to provide input/output (I/O) connections to and from integrated circuits (ICs) and to provide interconnection between the components on the system board level while physically supporting the electronic device and protecting the assembly from the environment. In order to increase the functionality and the miniaturization of the current electronic devices, these IC devices have not only incorporated more transistors but have also included more active and passive components on an individual chip. This has resulted in the emerging trend of a new convergent system[1] Currently, there are three main approaches to achieving these convergent systems, namely the system-on-chip (SOC), system-in-package (SIP) and system on package (SOP). SOC seeks to integrate numerous system functions on one silicon chip. However, this approach has numerous fundamental and economical limitations which include high fabrication costs and integration limits on wireless communications, which due to inherent losses of silicon and size restriction. SIP is a 3-D packaging approach, where vertical stacking of multi-chip modules is employed. Since all of the ICs in the stack are still limited to CMOS IC processing, the fundamental integration limitation of the SOC still remains. SOP on the other hand, seeks to achieve a highly integrated microminiaturized system on the package using silicon for transistor integration and package for RF, digital and optical integration[1] IC packaging is one of the key enabling technologies for microprocessor performance. As performance increases, technical challenges increase in the areas of power delivery, heat removal, I/O density and thermo-mechanical reliability. These are the most difficult challenges for improving performance and increasing integration, along with decreasing manufacturing cost. Chip-to-package interconnections in microsystems packages serve as electrical interconnections but often fail by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that integrated chip (IC) packages will have interconnections with I/O pitch of 90 nm by the year 2018 [2]. Lead-based solder materials have been used for interconnections in flip chip technology and the surface mount technology for many decades. The traditional lead-based and lead-free solder bumps will not satisfy the thermal mechanical requirement of these fine pitches interconnects. These electronic packages, even under normal operating conditions, can reach a temperature as high as 150C. Due to differences in the coefficient of thermal expansion of the materials in an IC package, the packages will experience significant thermal strains due to the mismatch, which in turn will cause lead and lead-free solder interconnections to fail prematurely. Aggarwal et al [3] had modeled the stress experienced by chip to package interconnect. In his work, he developed interconnects with a height of 15 to 50 micrometre on different substrate using classic beam theory. Figure 1 shows the schematic of his model and a summary of some of his results. Although compliant intrerconect could reduces the stress experienced by the interconnect, it is still in sufficient. Chng et al. [4] performed a parametric study on the fatigue life of a solder column for a pitch of 100micrometre using a macro-micro approach. In her work, she developed models of a solder column/bump with a pad size of 50micrometre and heights of 50 micrometre to 200 micrometre. Table I shows a summary of some of her results. Table 1.1: Fatigue life estimation of solder column chip thickness (micrometre) 250 640 640 640 board CTE (ppm/K) 18 18 10 5 solder column height (micrometre) Fatigue life estimation/cycle) 50 81 N.A 171 3237 100 150 27 276 3124 150 134 31 518 4405 200 74 38 273 5772 It can be seen from Table 1.1 that the fatigue lives of all solder columns are extremely short. Apart from the 5ppm/K board where there is excellent CTE matching, the largest fatigue life of the solder column is only about 518 cycles. As expected, the fatigue life increases significantly when the board CTE decreases from 18ppm/K to 10ppm/K and as the height increases from 50micrometre to 200micrometre.This is mainly due to the large strain induced by the thermal mismatch as shown in Figure 1.2. The maximum inelastic principal strain was about 0.16 which exceeds the maximum strain that the material can support. Although the fatigue life of the chip to package interconnection can be increases by increasing the interconnects height, it will not be able to meet the high frequency electrical requirements of the future IC where they need to be operating at a high frequencies of 10-20 GHz and a signal bandwidth of 20 Gbps, By definition, nanocrystalline materials are materials that have grain size less than 100nm and these materials are not new since nanocrystalline materials have been observed in several naturally-occurring specimens including seashells, bone, and tooth enamel [5, 6]. However, the nanocrystalline materials have been attracting a lot of research interest due to its superior mechanical and electrical properties as compared to the coarse-grained counterpart. For example, the nano-crystalline copper has about 6 times the strength of bulk copper [7]. Furthermore, the improvement in the mechanical properties due to the reduction in grain size has been well-documented. Increase in strength due to the reduction in grain-size is predicted by the Hall-Petch relationship which has also been confirmed numerically by Swygenhoven et al [8] and was first demonstrated experimentally by Weertman [9]. The implantation of nanocrystalline copper as interconnect materials seems to be feasible from the processing viewpoint too. Copper has been used as interconnects materials since 1989 whereas nano-copper has also been widely processed using electroplating and other severe plastic deformation techniques in the past few years. For instance, Lu et al. [10] have reported electroplating of nano-copper with grain size less than 100 nm and electrical conductivity comparable to microcrystalline copper. Furthermore, Aggarwal et al [11] have demonstrated the feasibility of using electrolytic plating processes to deposit nanocrystalline nickel as a back-end wafer compatible process. However, there are certain challenges regarding implantation of nanocrystalline copper as interconnects materials. As discussed above, nanocrystalline copper have a high potential of being used as the next generation interconnect for electronic packaging. However, it is vital to understand their material properties, deformation mechanisms and microstructures stability. Although the increase in strength due to the Hall-Petch relationship which has also been confirmed numerically and experimentally by Weertman [9], the improvement in the fatigue properties is not well documented and no model has been established to predict/characterize these nano materials in interconnection application; conflicting results regarding the fatigue properties have also been reported. Kumar et al [12] reported that for nano-crystalline and ultra-fine crystalline Ni, although there is an increase in tensile stress range and the endurance limit, the crack growth rate also increases. However, Bansal et al. [7] reported that with decreasing grain size, the tensile stress range increases but the crack growth rate decreases substantially at the same cyclic stress intensity range. Thus, nanostructured materials can potentially provide a solution for the reliability of low pitch interconnections. However, the fatigue resistance of nanostructured interconnections needs to be further investigated. Since grain boundaries in polycrystalline material increases the total energy of the system as compare to perfect single crystal, it will resulted in a driving force to reduce the overall grain boundary area by increasing the average grain size. In the case of nanocrystalline materials which have a high volume fraction of grain boundaries, there is a huge driving force for grain to growth and this presented a presents a significant obstacle to the processing and use of nanocrystalline copper for interconnect applications. Millet et al [13] have shown, though a series of systematic molecular dynamics simulations, grain growth in bulk nanocrystalline copper during annealing at constant temperature of 800K can be impeded with dopants segregated in the grain boundaries regions. However, it has been observed that stress can trigger grain growth in nanocrystalline materials [14] and there is no literature available on impeding stress assisted grain growth. There is an impending need to investigate the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth Dissertation Objectives The goal of present project is to develop a model for the fatigue resistance of nano-materials that have been shown to have superior fatigue resistance. Accordingly, the following research objectives are proposed. Develops a model for predicting fatigue life of nanostructured chip-to-package copper interconnections Develops a fundamental understanding on the fatigue behavior of nanocrystalline copper for interconnect application Addresses the issue on the stability of nanocrystalline materials undergoing cyclic loading Overview of the Thesis The thesis is organized so that past research on nanocrystalline materials forms the basis of the understanding and new knowledge discovered in this research. Chapter 2 reviews much of the pertinent literature regarding nanocrystalline materials, including synthesis, deformation mechanisms, and grain growth. Chapter 3 describes a detailed overview of the technical aspects of the molecular dynamics simulation method including inter-atomic potentials, time integration algorithms, the NVT NPT, and NEPT ensembles, as well as periodic boundary conditions and neighbor lists. Include in this chapter is the algorithms for creating nanocrystalline materials used in this dissertations.. Chapter 4 describes the simulation procedure designed to investigate and develop the long crack growth analysis. The results of the long crack growth analysis will be presented at the end of Chapter 4. Chapter 5 presents the result and discussion on mechanical behavior of single and nanocrystalline copper subjected to monotonic and cyclic loading whereas Chapter 6 presents the result and discussion on the impediment to grain growth caused by the dopant during fatigue/stress assisted grain growth. Finally, conclusions and recommendations for future work are presented in Chapter 5. Chapter 2 This chapter offers an expanded summary of the literature published with regards to the fabrication methods, characterization, and properties of nanocrystalline materials in addition to a description of existing interconnect technology. 2.1 Off-Chip Interconnect Technologies Chip-to-package interconnections in microsystems packages serve as electrical interconnections but they will often failed by mechanisms such as fatigue and creep. Furthermore, driven by the need for increase the system functionality and decrease the feature size, the International Technology Roadmap for Semi-conductors (ITRS) has predicted that interconnections of integrated chip (IC) packages will have a I/O pitch of 90 nm by the year 2018 [2]. The International Technology Roadmap for Semiconductors (ITRS) roadmap is a roadmap that semiconductor industry closely follows closely and its projects the need for several technology generations. The package must be capable of meeting these projections in order for it to be successful. This section reviews some of the current interconnect technology. Wire bonding [15] as shown in Figure 2.1, is generally considered as one of the most simple, cost-effective and flexible interconnect technology. The devices on the silicon die are (gold or aluminum) wire bonded to electrically connect from the chip to the wire bond pads on the periphery. However, the disadvantages of wire bonding are the slow rate, large pitch and long interconnect length and hence this will not be suitable for high I/O application. Instead of wires in the wire bonding, tape automated bonding (TAB) is an interconnect technology using a prefabricated perforated polyimide film, with copper leads between chip and substrate. The advantage of this technology is the high throughput and the high lead count. However, it is limited by the high initial costs for tooling. An alternative to peripheral interconnect technology is the area-array solution, as shown in Figure 2.3, that access the unused area by using the area under the chip. In area-array packaging, the chip has an array of solder bumps that are joined to a substrate. Under-fill is then fills the gap between the chip and substrate to enhance mechanical adhesion. This technology gives the highest packaging density methods and best electrical characteristics of all the avaiable interconnection technology. However, not only is its initial cost is high, it requires a very demanding technology to establish and operate. With the need for higher I/O density, compliant interconnects have been developed to satisfy the mechanical requirements of high performance micron sized interconnects. The basic idea is to reduce shear stress experienced by the interconnects through increasing their height or decreasing of its shear modulus (i.e. increases in their compliant) and hence the name compliant interconnects. Some of recent research in compliant interconnects include Tesseras Wide Area Vertical Expansion, Form Factors Wire on Wafer and Georgia Institute of Technologys Helix interconnects [17-19] as shown in Figure 2.4. Although compliant interconnects can solve the problem of mechanical reliability issue, they are done at the expense of the electrical performance. Since there is a need to reduce the packages parasitic through a decrease line delays, there is a need to minimize the electrical connection length in order to increase the system working frequency. Hence, compliant interconnect may not meet the high electrical frequency requirements of future devices. Figure 2.4: (a) Wide Area Vertical Expansion, (b) Wire on Wafer and (c) G-Helix [17-19] Lead and lead-free solders typically fail mechanical when scaled down to less than to a pitch of 100 mm. Compliant interconnections, on the other hand, do not meet the high frequency electrical requirements. The Microsystems Packaging Research Center at Georgia institute of Technology had demonstrated the feasibility of using re-workable nanostructure interconnections. Aggarwal et al [20] had show that nanostructured nickel interconnections, through a Flip Chip test vehicle, was able to improve the mechanical reliability while maintaining the shortest electrical connection length. However, the main disadvantages of this method was the significant signal loss at high frequency signal of nanocrystalline nickel [21]. As discussed above, nanostructure interconnects technology is the most promising interconnect technology to best meet the stringent mechanical and electrical requirement of next generation devices. However, there is a need of an alternate materials and a sensible choice of materials in this case would be nanocrystalline copper for its high strength material with superior electrical conductivity. Hence, it would be beneficial to use nanocrystalline-copper as material for the nanostructure interconnects. Due to the tendency for the grain to grow, there is a need to stabilize the grain growth in nanocrystalline copper before using it could be considered as a potential candidate for nanostructure interconnect. 2.2 Nanocrystalline material Nanocrystalline materials are polycrystalline materials with an average grain size of less than 100 nm [22]. Over the past decade , new nanocrystalline or nanostructured materials with key microstructural length scales on the order of a few tens of nanometers has been gaining a lot of interest in the material science research society. This is mainly due to its unique and superior properties, as compared to their microcrystalline counterparts which includes increased strength [22] and wear resistance [23]. These unique properties are due to the large volume fraction of atoms at or near the grain boundaries. As a result, these materials have unique properties that are representative of both the grain boundary surface characteristics and the bulk. Recent advances in synthesis and processing methodology for producing nanocrystalline materials such as inert gas condensation [24], mechanical milling [25, 26], electro-deposition [27], and severe plastic deformation [28] have made it possible to produce sufficient nanocrystalline materials for small scale application. 2.2.1 Synthesis Inert gas condensation, the first method used to synthesis bulk nanocrystalline [29], consists of evaporating a metal inside a high-vacuum chamber and then backfilling the chamber with inert gas [30]. These evaporated metal atoms would then collide with the gas atoms, causing them to lose kinetic energy and condenses into powder of small nano-crystals. These powders are then compacted under high pressure and vacuum into nearly fully dense nanocrystalline solids. The grain size distribution obtained from this method is usually very narrow. However, the major draws back of this method are its high porosity levels and imperfection bonding. Grain coarsening also occurs due to the high temperature during the compaction stage [31]. Mechanical milling consists of heavy cyclic deformation in powders until the final composition of the powders corresponds to a certain percentages of the respective initial constituents [25, 26]. A wide grain size distribution is obtained by this method. This technique is a popular method to prepare nanocrystalline materials because of its applicability to any material and simplicity. However, their main drawback includes contamination and grain coarsening during the consolidation stage. Electro-deposition consists of using electrical current to reduce cations of a desired material from a electrolyte solution and coating a conductive object on the substrate. Electro-deposition has many advantages over processing techniques and this includes its applicability to a wide variety of materials, low initial capital investment requirements and porosity-free finished products without a need for consolidation processing [27]. Furthermore, Shen et al. [32] and Lu et al.[33] had recently show that the right electro-deposition condition can produce a highly twinned structure which leads to enhanced ductility. The main drawback of this method is it is the difficulty to achieve high purity. Severe plastic deformation, such as high-pressure torsion, equal channel angular extrusion (ECAE), continuous confined shear straining and accumulative roll-bonding, uses extreme plastic straining to produce nanocrystalline materials by mechanisms such as grain fragmentation, dynamic recovery, and geometric re-crystallization [34]. It is the only technology that transformed conventional macro-grained metals directly into nanocrystalline materials without the need of potentially hazardous nano-sized powders. This is achieved by introducing very high shear deformations into the material under superimposed hydrostatic pressure. Two of the most commonly used methods are high-pressure torsion and ECAE [35]. In the study of the effect of ECAE on the microstructure of nanocrystalline copper, Dalla Torre et al [36] observed that the grains become more equi-axial and randomly orientation as the number of passes increases, as shown in Figure 2.5 Figure 2.5: Microstructure of ECAE copper subjected to (a) 1 passes (b) 2 passes (c) 4 passes (d) 8 passes (e) 12 passes and (f) 16 passes [36] 2.2.2 Mechanical Behavior of nanocrystalline materials Due to the small grain size and high volume fraction of grain boundaries, nanocrystalline materials exhibit significantly different properties and behavior as compared to their microcrystalline counterpart. The structure and mechanical behavior of nanocrystalline materials has been the subject of a lot of researchers interests both experimentally [37-43] and theoretically [44-50]. This section reviews the principal mechanical properties and behavior of nanocrystalline materials. 2.2.2.1 Strength and ductility Recent studies of nanocrystalline metals have shown that there is a five to ten fold increases in the strength and hardness as compared to their microcrystalline state [7, 36, 37, 51, 52]. This increase in the strength is due to the presence of grain boundaries impeding the nucleation and movement of dislocations. Since decreasing grain boundary size increases the number of barrier and the amount of applied stress necessary to move a dislocation across a grain boundary, this resulted in a much higher yield strength. The inverse relationship between grain size and strength is characterized by the Hall-Petch relationship [53, 54] as shown in equation (2.1). Eq (2.1) In equation (2.1), s is the mechanical strength, k is a material constant and d is the average grain size. Hence, nanocrystalline materials are expected to exhibit higher strength as compared to their microcrystalline counterpart. Figure 2.6 and Figure 2.7 show the summary of hardness and yield strength from tensile test that are reported in the literature. Indeed, hardness and yield strength of copper with a grain size of 10nm (3GPa) can be one order higher than their microcrystalline counterpart. To the larger specimens. Derivation from Hall-Petch relationship begins as the grain size approaches 30nm where the stresses needed to activate the dislocation multiplication via Frank-Read sources within the grains are too high and the plastic deformation is instead accommodated by grain boundaries sliding and migration.[12]. Furthermore, as the grain size reduces, the volume fraction of the grain boundaries and the triple points increases. Material properties will be more representative of the grain boundary activity [64] and this will resulting the strength to be inversely proportional to grain size instead of square roots of the grain size as predicted by Hall Petch relation [65]. Further reduction in the grain size will result in grain boundaries processes controlling the plastic deformation and reverse Hall-Petch effect, where the materials soften, will take place. Although sample defects had been account for the earlier experimental observation of reverse Hall-Petch effect[24], Swygenhoven et al [66] and Schiotz et al [47], using molecular simulation, was able to showed that nanocrystalline copper had the highest strength (about 2.3GPa ) at a grain size of 8nm and 10-15nm respectively. Conrad et al [67] pointed out that below this critical grain size, the mechanisms shifted to grain boundary-mediated from dislocation-mediated plasticity and this causes the material to become dependent on strain rate, temperature, Taylor orientation factor and presence of the type of dislocation. The yield stress of nanocrystalline copper was highly sensitive to strain rate even though it is a fcc materials. The strain rate sensitivity, m, in equation 2.2 a engineering parameter which measured the dependency of the strain rate and Figure 2.8 shows a summary of m as a function of grain size for copper specimen in the literature [51, 68-70]. Due to high localized dislocation activities at the grain boundaries which results in enhanced strain rate sensitivities in nanocrystalline materials, m increases drastically when the grain size is below 0.1 mm as shown in Figure 2.8. (2.2) Room temperature strain rate sensitivity was found to dependent on dislocation activities and grain boundaries diffusion [52, 71, 72]. Due to the negligible lattice diffusion at room temperature, the rate limiting process for microcrystalline copper was the gliding dislocation to cutting through forest dislocation, resulting in low strain rate sensitivities. However, due to the increasing presence of obstacles such as grain boundaries for nanocrystalline materials, the rate limiting process for smaller grain size was the interaction of dislocation and the grain boundaries, which is strain rate and temperature dependence. By considering the length scale of the dislocation and grain boundaries interaction, Cheng et al [52] proposed the following model for strain rate sensitivities . (2.3) z is the distance swept by the dislocation during activation, r is the dislocation density and a, a and b are the proportional factors. With this model, they will be able to predict higher strain rate sensitivities for nanocrystalline material produced by severe plastic deformation as compared to other technique. Since the twin boundaries in nanocrystalline or ultra fine grain copper served as a barriers for dislocation motion and nucleation which led to highly localized dislocations near the twin boundaries, the strain rate sensitivity of copper with high density of coherent twin boundaries was found to be higher than those without any twin boundaries [33]. Lastly, the increase enhanced strain rate sensitivity in nanocrystalline copper had been credited for it increases in strength and ductility. For example, Valiev et al [60] credited the enhanced strain rate sensitivity of 0.16 for the high ductility. In addition to a strong dependency on the strain rate, strength in nanocrystalline materials was also highly dependent on the temperature. Wang et al [73] observed that the yield strength for ultra fine grain copper with a grain size of 300nm increases from approximately 370MPa to 500MPa when the temperature reduces from room temperature to 77k. The authors attributed this increase in yield strength due to the absence of additional thermal deformation processes at 77k. This is consistent with Huang et al [74] observation where the temperature dependence of nanocrystalline copper with an increase in hardness of nanocrystalline copper with lowering the temperature is noted Ductility is another important characteristic of nanocrystalline materials. In microcrystalline materials, a reduction in grain size will increase the ductility due to the presence of grain boundaries acting as effective barriers to the propagation of micro-cracks[75]. However, nanocrystalline copper showed a lower strain to failure than that of their microcrystalline counterparts and this lacks in ductility was attributed to the presence of processing defects [76]. Recent advanced in processing of nanocrystalline materials offer materials with fairly good ductility in additional to ultra-high strength. Lu et al [10] reported that nanocrystalline copper with minimal flaw produced via electro-deposition had an elongation to fracture of 30%. Furthermore, Youssef et al [77] observed a 15.5% elongation to failure for defect free nanocrystalline copper produced via mechanical milling. Hence, it was possible for nanocrystalline copper to be both strong and ductile if the processing artifacts are minimized. The failure are usually consists of dimples several time larger than their grain size was normally found on the failure morphology of nanocrystalline materials and Kumar et al [78] presented the following model for initiation and hence the eventual failure of nanocrystalline materials. Furthermore, the presence of shear region was found to be due to shear localization since the ratio of strain hardening rate to prevailing stress was usually small [79, 80]. Figure 2.9: Schematic illustration of fracture in nanocrystalline material postulated by Kumar et al [78] 2.2.2.2 Creeps Nanocrystalline materials are expected to creep during room temperature. This is because Due to the higher fraction of grain boundaries and triple junctions, self diffusivity of nanocrystalline material had been shown to increase by an order of three as compared to microcrystalline copper [81]. Since creep behavior was dependent on grain size and diffusivity, with creep rate increases with an increase in diffusivity or a decrease in grain size, the creep temperature for nanocrystalline copper was known to be a small fraction of melting temperature (about 0.22 of its melting points). Furthermore, since creep had always been cited as one of the reason for grain size softening in nanocrystalline materials, creeps were other important mechanical properties of nanocrystalline materials that had been gaining a lot of researchers attention. Due to the high volume fraction of grain boundaries and enhanced diffusivity rate