مدلسازي ساختاري آلياژهاي حافظه دار فرومغناطيس

چكيده انگليسي :

Constitutive Modeling of Ferromagnetic Shape Memory Alloys Milad Shirani Milad jsb@gmail com Date of Submission January 8 2013 Department of Mechanical Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Dr Mahmoud Kadkhodaei kadkhodaei@cc iut ac ir Abstract Smart materials have received much attention to be employed as sensors and actuators in various industrial and biomechanical applications given their special capabilities of interconverting different forms of energy Among smart materials there has especially been much research effort in constitutive modeling of shape memory alloys SMA s due to their special behavior and high strain capabilities A branch of these alloys that has recently attracted the attention of researchers is able to create strain in a magnetic field in addition to processing the conventional behaviors of shape memory alloys These materials are termed ferromagnetic memory alloys FSMA s Several attempts have hitherto been made to study their behaviors subjected to combined loadings of magnetic fields and mechanical stresses The existing models are in implicit forms and require rather long numerical solutions The main goal of this thesis is to provide an explicit model able to predict the behaviors of these materials under any loading conditions The proposed model is both simple and capable of being used without the need of incremental numerical solutions In order to attain the proposed model for FSMA s the accepted definitions and assumptions used for modeling SMA s are first discussed Furthermore conditions are introduced where current models in SMA s produce conflicting results against experimental data Some experiments are also done to examine the existing models and assumptions regarding SMA s Moreover incompatibility of these models with actual data is shown Thereafter an explicit model based on continuum mechanics is presented which is capable of simulating SMA s behavior when subjected to phase transformations In this model the effect of loading history on the onset of phase transformation is taken into account Therefore according to the obtained supportive experimental data transformation surfaces are introduced in place of the existing phase The proposed explicit model for FSMA s is also based on continuum mechanics and is capable of predicting the behavior of these materials subjected to stress and magnetic fields In order to examine the suggested model relevant experiments are conducted on a Ni Mn Ga ferromagnetic shape memory alloy The obtained results nicely fit the experimental findings indicating the validity of this approach In addition to the simplicity of its usage a prominent feature of the new model is the way it accounts for the loading history effects on the conditions of initiation of inelastic strain The proposed transformation surfaces are defined in such a way that is able to study all possible loadings At last the behaviors of these materials subjected to biaxial loadings are examined and a model capable of predicting their behavior under such conditions is proposed for the first time Keywords Ferromagnetic shape memory alloy constitutive model transformation surface Shape memory alloy loading history phase diagram

شيراني، ميلاد

مدلسازي ساختاري آلياژهاي حافظه دار فرومغناطيس

تاريخچه بارگذاري , دياگرام فازي