Energy dissipation of shock-generated stress waves through phase transformation and plastic deformation in NiTi alloys

Abstract

The interaction between propagation of shock-induced stress waves and phase transformation in Nickel–Titanium (NiTi) shape memory alloys is studied experimentally and computationally. Molecular dynamics simulations at the atomistic scale are utilized to investigate how the local phase transformations dissipate the energy of shock waves as they travel in the material. It is shown that plastic deformations also happen at the vicinity of the regions at which the loading is applied. While plastic deformations also contribute in the energy dissipation, our results show that the energy dissipation is prominently induced by the reversible phase transformation. These results affirm that shape memory alloys are superior candidates for dissipating the energy of shock loads, with minimal permanent deflections remaining on the structure after the load is applied. Experiments are also performed in which precise and controlled shock loads (generated by the pressure of the liquid jet produced by the collapsing of a spark-generated bubble) are applied to two bars made of NiTi and Aluminum. Our results show that both the measured strain and lateral displacements are drastically damped in NiTi bars, which confirms the dissipation of stress shock ways due to phase transformation in these alloys.