In-situ investigation of dynamic deformation in NiTi shape memory alloys under laser induced shock

Abstract

The free surface particle velocity of NiTi target shocked with a pulsed laser beam was measured with a photonic Doppler velocimetry (PDV) system to study the dynamic deformation behavior of NiTi alloys at ultra-high strain rate of 10 6 ∼10 7 /s. Through the analysis of the particle velocity profiles, the shock wave intensity was found to have the influence on the process of austenite-martensite transformation. Theoretical analysis of shock wave propagation showed that the first plateau in the velocity profile was caused by martensitic transformation and the second plateau if existing is caused by the subsequent plastic yielding of shock induced martensite. Residual martensite of the NiTi, which exhibited as needlelike structures, was observed in the laser shocked region. Based on the present results, and the studies by Nemat-Nasser et al. (2005), Liao et al. (2012), and Wang et al. (2013), we concluded that laser induced shock can cause the martensitic transformation as long as the laser induced shock pressure reaches a critical value. The dynamic transition stress and the dynamic tensile strength of NiTi alloys were also determined from the experimentally measured surface velocity profile.

Phase Transformation, Twinning, and Detwinning of NiTi Shape-Memory Alloy Subject to a Shock Wave Based on Molecular-Dynamics Simulation

“…However, the stress plateau gradually disappears with an increasing strain rate, which has been confirmed by Nemat-Nasser S. et al [48,49]. Wang et al provided direct experimental evidence that stress-induced martensite transformation occurs in NiTi SMA undergoing laser-shock peening, where the strain rate is approximately 10 7 s −1 [50,51]. It is concluded that the mechanism of stress-induced martensite transformation at an ultra-high strain rate is obviously different from that at a low strain rate.…”

Molecular Dynamics Investigation of the Influence of Voids on the Impact Mechanical Behavior of NiTi Shape-Memory Alloy

“…Many researchers have demonstrated that stress-induced martensitic phase transformation of NiTi shape-memory alloys may occur during tensile, compressive, and shear loading [ 32 , 33 , 34 ]. Wang et al [ 35 , 36 ] provided experimental evidence that NiTi shape-memory alloys undergo stress-induced martensitic transformation when subjected to laser impact strengthening, and its strain rate is about 10 7 s −1 . Their results suggest that the mechanism of stress-induced martensitic phase transformation at ultra-high strain rates is significantly different from that at low strain rates.…”

A review on Nitinol shape memory alloy heat engines

“…Martensite variants can be twinned (M t ) and de-twinned (M d ). The reversible transformation from austenite to martensite [46] and vice versa results in SMA behavior [49], and it is known that the martensitic transformation can be caused by both temperature and stress [50], which are referred to as SME and pseudoelasticity, respectively [51][52][53]. The essential actuating ability of the NiTi SMA heat engine is a consequence of the pseudoelastic and SME of SMA material.…”