Study Of Pseudoelastic TiNi Alloy On Theory,Experiment And Numeric

As a function material, shape memory is widely applied to biomedicine,intelligent component,shake resist structure etc. because of its superiority such as shape memory effect(SME) and pseudoelastic effect(PE). TiNi shape memory alloys also named Nitinol , which were discovered first in 1970s, are the most widely used type of shape memory today. In this paper the static and dynamic behavior of TiNi alloy is systematically investigated using theoretical,experimental and numerical methods.Principle of the phase transition is pointed out in macro and micro, and the main parameters in phase transition is described. Special behaviors, such as martensite reorientation,asymmetry of tension and compression,deformation localization and instability are described. DSC curves and characteristics temperatures of Ti-50.9at% Ni alloy with various heat treatments are acquired in experiments . The best heat treatment methods of Ti-50.9at.%Ni alloy are acquired to obtain shape memory effect and pseudoelastic effect under the normal temperature.Mechanical experiments and cyclic loading tests are carried out in various temperatures,strain rates and loading cases within strain rate of 10^-1/s. Physical parameters, such as the phasetransition start stress, residual strain, modulus of austenite and martensite, hysteresis area, etc. are acquired. Principles of TiNi alloy's strain rate effect and temperature effect are got within strain rate of 10^-1/s. In a certain temperature range, TiNi show the temperature enhanced effect and temperature effect of pseudoelastic platform. A curve fit pattern of constitutive relation considering the temperature effect and strain rate effect is gave out, which fit well with experiments.Experiments performed in Tensile Impact Apparatus in the strain rate range of 10²ï½ž10³/s and performed in the split hopkinson bar in the strain rate range of 10³ï½ž2×10³/s are carried out. A comprehensive study has been done on the dynamic compression behaviors and the dynamic tensile behaviors. Phasetransition start stress hardly changes and phasetransition termination stress increases as strain rate increases based on the SHPB experiments. Through the specimen test after SHPB experiments, we found that the ac tual residual deformation of the specimen is too small to be taken into account, which shows good recoverability of TiNi alloy. Fracture time and fracture strain is found strain rate dependent in experiments performed in Tensile Impact Apparatus and possible causes are given.Researchs are made on the self-made damping device , which is designed based on TiNi alloy. Relations between the system natural frequency and amplitude,pre-strain or temperature are discussed. When the strain is within a certain range ( less than 3%), the amplitude the larger the damping ratio the greater the energy-sapping the sooner. We found that appropriate pre-strain can effectively improve the damping ratio, and a design of shape memory spring is gave.Constitutive relation of shape memory alloy is derived based on thermo dynamics,mechanics and martensitic transformation, and several different phasetransition functions (cosine form, cubic polynomial, quadratic polynomial) are applied to the constitutive relation. The new constitutive model is checked well through contrasting with classical phenomenological constitutive model and experiments.A three-dimensional constitutive relation of shape memory alloy is derived based on the plastic mechanics. After that, this three-dimensional is imported into ABAQUS through the secondary development interface. Numerical simulations are made to simulate the MTS experiments and consistency with experiments is maintained.Detailed numerical simulation of 45# steel bullet impacting pseudoelastic cantilever of TiNi is made based on Dr. Zhang Xinghua' experiments using DYNA software. The numerical result is verified correct through contrasting main parameters (such as cantilever' s maximum deflection,the bullet residual velocity and other parameters)with experiments. Then phenomena which are difficult to observe in experiments (such as bending wave propagation,beam energy changes, etc.) are analyzed and some useful conclusions are obtained.