Experimental and Numerical Analysis of Recovery Stress in Ni₄₇Ti₄₄Nb₉ Shape Memory Alloys: Application to Tightening Available to Purchase

Ni₄₇Ti₄₄Nb₉ Shape Memory Alloys (SMAs) are widely considered for tightening applications. The alloy is composed of a NiTi SMA matrix containing niobium precipitates. A specific thermomechanical treatment strongly increases the transformation hysteresis in these alloys, what improves the tightening efficiency. Tightening pressures exhibited by Ni₄₇Ti₄₄Nb₉ rings are experimentally investigated. Strain gage measurements allow to monitor the tightening pressure using a home test bed. Evolutions with temperature are recorded. A thermo-mechanical constitutive law, specific for Ni₄₇Ti₄₄Nb₉, is proposed. It is based on the Mori-Tanaka scale transition technique by considering the precipitates as elastic-plastic inclusions embedded in the SMA matrix. The resulting effective law is implemented, and validated in ABAQUS via UMAT subroutine. Experimental tests are simulated by Finite Element Modeling, and comparisons are performed.