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چكيده انگليسي :

Study the effect of stress concentration on stress strain response of SMA wires Mehdi Kamrani m kamrani@me iut ac ir Date of Submission 2012 3 4 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Mahmood Kadkhodaei kadkhodaei@cc iut ac irAbstract Several definitions for shape memory alloys have been proposed but as the simplest definition one cansay these alloys are a group of materials in which permanent strain could be completely recovered due toheating Of course this is just one of the significant characteristics of these alloys called Shape memoryeffect Another characteristic of these alloys is Psuduelastic in which strain due to loading at hightemperatures recovers during unloading Nowadays these alloys have variable uses in different industriessuch as medical aerospace and robotics technology In this thesis thermomechanical behavior of these alloysin psuduelastic mode is studied Since these alloys have vast usage in the form of wire for example asactuators simulation of their behavior under tensile test is studied in this thesis Providing usual dogbone sample for tensile test out of these alloys is impossible because it makes the simulation far from reality Moreover the required machining for producing this shape affects the behavior of these alloys On the otherhand there is no modified standard for tensile test with circular samples So at first using a finite elementsimulation maximum applicable force on wire before the occurrence of slip is proposed Stress concentrationcaused by grippers over wire could dramatically affect the behavior of these materials So a simple study tookplace on the span of this stress concentration based on which a minimum length is proposed for tensile test ofthese materials For modeling the behavior of these materials under tensile test at first the effect of martialparameters on the stress distribution along the length of wire is studied Then using a finite elementsimulation on tensile test of an elastic wire the stress distribution along the length is obtained and used forsimulation of a shape memory alloy Using this stress distribution and a temperature distribution proposed bya thermomechanical model tensile test is modeled Finally a simple method for predicting stress distributionalong the length is proposed and used for modeling the behavior of these materials to simulate the tensile testmore exactly With this method finite element simulation of fastening the grippers when the wire is stillelastic is utilized After this step stress and radius distributions are calculated by the proposed model Usingthis stress distribution along with temperature distribution again behavior of these materials under tensile testis simulated The predicted stress strain and local nominal strain curves are compared to the experimentalresults The very good agreement between the results showed the ability of the proposed model in predictingthe effect of changes in material parameters and conditions of surrounding media Keywords Thermomechanical model Shape memory alloys Finite element local global strain

كامراني، مهدي

بررسي اثر تمركز تنش بر رفتار مكانيكي سيم هاي حافظه دار

مدل ترمومكانيكي , اجزاي محدود , كرنش محلي-اسمي