مدل سازي ترموديناميكي كاملا كوپله چند محوره آلياژهاي حافظه دار و پياده سازي عددي به روش اجزاي محدود

چكيده انگليسي :

Fully Coupled Thermomechanical Modeling Of Shape Memory Alloys under Multiaxial Loadings and Implementation by Finite Element Method Mostafa Salehan m salehan@me iut ac ir August 22 2015 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor M Kadkhodaei Assoc Prof kadkhodaei@cc iut ac irAbstractShape memory alloys SMAs are a branch of smart materials which have unique properties including twoimportant features pseudoelasticity and shape memory effect Shape memory effect is the recovery of permanentstrains due to heating Pseudoelasticity is the ability of material to recover large strains after the unloading process Magnitude of these recoverable strains is up to 10 These two important properties are due to alloy structure andtwo solid state phases austenite and martensite Austenite phase has high symmetry and high temperature and hasmore energy than martensite phase which has low symmetry and low temperature Martensitic transformationbetween these two phases occurs due to heatting or stress SMA s have also variety of properties such as high powerto weight ratio energy damping and biocompatibility and are used in various industrial applications These wideapplications lead the necessity of modeling and simulation of SMA s Different constitutive models have beenpresented for these alloys and different numerical approaches for the implementation of these models have beenused Most of the existing models are 1D and their solutions are only applicable for SMA wires lonely or forparticular simple types of structures consisting SMA wires Since smart structures consisting SMAs are various andhave general geometries 3D modeling and solutions is a necessity In the last decades some 3D models have beenprovided Most of 3D models are used for special geometries and load conditions These special case studies are nolonger effective in general cases Coupled thermomechanical behavior of these materials is a challenge in modeling This behavior occurs in high strain rates and dynamic loadings In this situation the isothermal assumption is notvalid and is needed to take account the temperature changes In present research an approach for modeling and implementing fully coupled thermomechanical behavior undermultiaxial loadings is provided This model includes both shape memory effect and pseudoelasticity and is able tosimulates any thermal and multiaxial mechanical loading path Also present model takes account thethermomechanical coupling and rate dependency of SMAs The model implementation is carried out by ABAQUScommercial finite element package Constitutive and energy relations are introduced into ABAQUS via a usermaterial subroutine UMAT The model can investigate different problems with various boundary conditions geometries and loadings In order to validate the model and UMAT model results are compared with resultsobtained from experimental analytical and numerical efforts reported in the references The comparison shows agood agreement in model results The effect of different loading rates is investigated Also the effects of thermalboundary conditions on temperature gradient are observed Then the effect of 3D geometry in a bar is investigated and the results show the temperature gradient in cross section of bar and thus a different stress strain curve in barcenter and its surface is observed As a case study helical springs are investigated and the model shows a goodagreement in quasi static loadings In high loading rate the behavior of helical spring is different from that of quasi static condition The results show that in loadings with high strain rate latent heat is a key parameter In thisresearch the effect of latent heat is take into account explicitly KeywordsShape Memory alloy SMA Multiaxial loading Fully coupled thermomechanical behavior Latent heat Finite element ABAQUS UMAT

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مدل سازي ترموديناميكي كاملا كوپله چند محوره آلياژهاي حافظه دار و پياده سازي عددي به روش اجزاي محدود

بارگذاري چند محوره , گرماي نهان استحاله , آباكوس , يومت