| The present study for shape memory alloy materials,a focus on the influence of heat treatment on martensitic transformation and super elasticity,and the effect of heat treatment on its mechanical properties especially on the modulus of elasticity is relatively l ess.On the other hand,focused on the theoretical model,finite element simulation,factors affecting the mechanical behavior of stress and strain and the evolution of microstructure.However,the research on the quantitative measurement and deformation mechanism of the shape memory alloy material in the whole field,especially the microscopic deformation is not obvious.In this paper,the mechanical properties of NiTi shape memory alloy after heat treatment and the quantitative measurement of NiTi shape memory alloy were studied.Digital image correlation method(DIC)through related processing on image deformation before and after the displacement and strain field of the surface,is a real-time full non-contact method for measuring the deformation.which has become one of the most used optical measurement technology widely.As the necessary carrier of digital image correlation,speckle quality has an important influence on the measurement accuracy.For the NiTi alloy,even after a high temperature treatment and the grain size is only about 70-80mm.So to study the micro mechanical behavior of NiTi shape memory alloy need to produce more suitable micro nano speckle.In view of the above problems,the main research work of this paper is as follows:The effects of different heat treatment processes on the mechanical properties of the alloy,such as elastic modulus,Poisson’s ratio,yield strength and tensile strength were analyzed.At the same time,the microstructure of the samples was observed by metallographic microscope and the grain size was estimated.The effects of grain size and phase transformation on the mechanical properties of NiTi alloy were analyzed.The results show that the NiTi alloy was 850°C solid solution treatment 1h,aging treatment of 6h in the 550°C,the mechanical properties are greatly improved,providing experimental basis for the selection of NiTi alloy heat treatment process parameters.The development and basic principle of digital image correlation method are introduced,that study on the fabrication of micro nano speckles of the deformation carrier.On the basis of the fabrication technology of micro speckle by centrifugal casting,by optimizing the particle size,the influence of the ratio of powder to epoxy,centrifugal speed,curing time,the rate of gelation and the time of gelation were studied,and the optimal speckle process parameters are obtained.It was found that the particle size was smaller and more suitable for the measurement of the deformation of NiTi alloy grain and grain boundary,by compared with the strain gauge measurement of elastic modulus,to verify the accuracy of the micro speckle.The crystal mechanical behavior and micro fracture mechanics behavior of NiTi shape memory alloy were studied by means of the digital image correlation deformation measurement technology.Which is provide experimental data and experimental method to establish a shape memory alloy microstructure theory model and reliability design and verification. |
