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چكيده انگليسي :

Investigation on the Behavior of SMA Wires under Cyclic Loadings Omid Hossein Abrishami Omidhosein abrishami@gmail com December 5 2011 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 IranDgree M Sc Language FarsiSupervisor M Kadkhodaei Assist Prof kadkhodaei@cc iut ac irAbstractSMAs are widely used for having two properties of shape memory and superelasticity These alloys are usuallyavailable as wires and go under cyclic loadings in some practical applications one of which could be indicatedas the training process for creating two way shape memory effect TWSME Training in the form of applyingcyclic loads until obtaining stabilized response and hence stability of non elastic strains in SMA is one of themost effective achieving methods for getting TWSME Using these alloys as dampers for controllingmechanical vibrations due to their high damping capacities is another case for imposing SMAs to cyclic loads Hence the importances of studying and identifying SMAs behaviors under cyclic loadings are considered morethan before Thermo mechanical coupling in shape memory alloys SMAs and its effect on high strain rates causetemperature variation of SMA during cyclic loadings Temperature variation leads to dependence of cyclicresponses of SMA in each cycle to previous ones So in analyzing cyclic responses in either transient or stablestates resolving all the previous cycles would be needed that it often leads to solving time consuming andcomplex equations Although the loading condition in most of the studies on these alloys are assumed to bequasi static in the subject of investigating cyclic behaviors consideration of models depending on the strain rateis inevitable In this thesis Firstly a 1 D thermo mechanical model is proposed and equations in continuum mechanicsframework are extracted for stress controlled and strain controlled loadings By developing a code inMATLAB the boundary value problem is numerically solved and cyclic responses are extracted and comparedwith Kadkhodaei et al results Validation of equations and their results are showed by carrying out experimentaltests on a nitinol wire in stress controlled and strain controlled cyclic loadings and proper agreement wasobserved between numerical results and experimental findings The second part corresponds to the idea presented in order to cut the dependence of responses to temperatureand predicting the number of loading cycles until getting stabilized response without solving all loading cycles By assuming fixed temperature during cyclic loadings the non quasi static loading case may be behaved similarto the quasi static state but SMA properties should be changed in such a way that prediction of the non staticresponses at each instant of loading is possible A pattern for variations in the mentioned properties and thenumber of loading cycles until getting stabilized response in different strain rates is proposed The relations ofthe properties variations and the sensitivity of these relations coefficients to the loading situation are alsoinvestigated The effects of transformation temperatures and wire diameter on variation of these parameters arealso studied Through the present approach in this research non static loading condition of SMA wires have the samesuch a condition the effect of displacing behavior as the quasi static state and the existing phase transformation relations could be used However inwith slope in phase diagram are considered in order to predict SMA behaviors properly without solving and lines and the effect of rotation of transformation stripscomplex thermo mechanical equations Key WordsShape Memory Alloys SMAs Cyclic loading Strain rate dependency Thermo mechanicalcoupling Training

ابريشمي، اميدحسين

بررسي رفتار سيم حافظه دار در بارگذاري هاي چرخه اي

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