Modelling of mechanical behaviour of shape memory alloys using finite elements method

Abstract

Superelastic behaviour of Ni-Ti alloy wire under variable amplitude loading was simulated and experimentally studied. Mechanical properties and phase transformation stresses ( , , , ) of the material were obtained in uniaxial tensile test. The wire of 55,8% Ni -44,2% Ti alloy with a diameter of 1,5 mm and a working length of 30 mm was tested at room temperature (+ 16°C) on the air. On the base of finite elements method, using ANSYS the stress-strain dependencies on each loading cycle were calculated. The stressphase transformation are changes under a variable amplitude loading. The simulated stress-strain dependencies were compared with the experimental ones. The maximum error, being compared with experimental data, does not exceed 10,9%. The calculated dependences of elastic strain and dissipated energies on the amplitude stress are well agreed with experimental data. The obtained results are of theoretical and applied interest for modelling the superelastic behaviour of SMA under variable amplitude loading.Statement of the problem. Development of science and technology promotes the appearance of new and advanced requirements for application of materials, their strength and durability characteristics. Shape memory alloys (SMA) are used in many branches of industry thanks to the shape memory effect, good damping properties, durability and strength characteristics [1 -6]. The nickel-titanium alloy can «remember» its original shape and return it in the original non-deformed state after unloading (the effect of pseudoelasticity) or heating (the effect of shape memory) during many cycles of loading and unloading.Analysis of available results of investigations. The shape memory alloy Nitinol -(Ni-Ti) was created in the 1960-ies at Naval Ordnance Laboratory (USA) and soon was widely used in medicine and different branches of engineering [1 -4]. Many papers are devoted to the pseudoelesticity modelling and the shape memory effect of such alloys, the study of which is presented in the paper [7] in particular. The 3D model of the shape of the shape memory alloys behaviour for ANSYS makes possible to take into account the decrease of rigidity of the structural element during transition from austenite to martensite [8]. The 3D SMA model [9], which presents the pseudoelestic behaviour and the shape memory effect and makes possible to model, using the finite elements method, the behaviour of free-extended stents and spring working elements, is presented.The Objective of the paper. To model the pseudoelastic behaviour of nickel-titanium alloy, using the finite elements method (FEM), under the variable amplitude of loading and compare it with the experimental results.Statement of the task. Mechanical behaviour of SMA is specified by the microstructure characteristics, containing two different phases, austenite and martensite.Modelling of mechanical behaviour of shape memory alloys using finite elements method 8 ….