Dynamic deformation behavior of TiNi (superelastic grade) and TiNiCu alloy (shape memory grade) were examined using Split Hopkinson Pressure Bar. The stress-strain curves of the TiNi alloy exibits strain rate sensitivity. The flow stress in the plateau region increased with increasing of strain rate logarithmically, and the on-set stress for stress induced martensite also increased slightly. In contrast, the stress-strain curve of the TiNiCu alloy was found to be much less sensitive to strain rate. TEM observations revealed that the microstructure of the dynamically deformed TiNi is similar to that of the sample before dynamic deformation. In contrast, the dynamically deformed TiNiCu has a fine twinned structure than the sample deformed statically.
Analytical constitutive equation for the dynamic deformed TiNi alloy was proposed by addition of the terms concerning the strain rate effect and temperature change due to adiabatic deformation and latent heat of martensitic transformation, the revised constitutive equation was in a good agreement with the experimental results.
The buckling behavior of TiNi Shape Memory Alloy (SMA) plates is evaluated numerically and experimentally with aim of using TiNi as an Energy Absorption (EA) material. To this end, we performed FEM analysis for TiNi plates of several thickness and length. The present analytical study shows promising result of using TiNi as an EA material. This is confirmed by the experiment work. The post-buckling shape and the load-displacement relationship are quite different from those of conventional materials such as aluminum and steel. Post-buckling strength of the conventional materials decreases gradually with increase in applied loading (or deformation). This reduction in the load bearing capacity at higher loads is attributed to the localized high strain in deformed specimen under compression while the majority of the specimen volume deform at modest strain. If this localized high strain is avoided and high straining can be made more uniformly in the entire specimen under compression load, then such a plate is expected to exhibit large energy absorption, i.e. a new EA material. The present study reveals that the energy absorption in TiNi plate under compression is 3 times larger than that of aluminum plate for the same level of compression loading.