Dynamic Behavior and Shock Absorption Properties of Porous Shape Memory Alloys

Abstract

Abstract : Two methods for producing porous NiTi shape memory alloy (SMA) were used in this work: conventional sintering and sintering at elevated pressure using a Hot Isostatic Press. Depending on various parameters such as sintering times and temperatures, as well as initial powder size and compaction, porous specimens have been produced with varying average pore sizes. The phase transformation temperatures of the porous NiTi specimens were determined using a Differential Scanning Calorimeter, while their microstructure and phase compositions were analyzed using X-Ray Diffraction and a Scanning Electron Microscope aided with Electron-Probe Micro Analysis. Quasi-static and dynamic tests under compression were carried out on various porous NiTi samples to evaluate the pseudo-elasticity and the martensitic detwinning behavior. The effective response of the porous SMAs was modeled using micromechanical averaging techniques. The current work establishes a macroscopic constitutive model for the porous SMA material using the properties of the dense SMA and information about pore shape, volume fraction as well as given pore orientation. A constitutive model for the SMA matrix, which is capable of accounting for the development of plastic strains, was developed as part of the modeling effort. The results from the numerical simulations were compared with the experimental data.