Experimental and numerical analysis of recovery stress in shape memory alloys: application to tightening

Shape Memory Alloys (SMA) are widely considered for tightening applications. The most common one are shape memory rings whose diameter decreases during heating. The alloy is composed of a NiTi matrix containing niobium precipitates. A specific thermomechanical treatment increases by more than one hundred degrees the transformation temperature hysteresis, what increases the range of use and improves the tightening efficiency. Tightening pressures exhibited by rings with two various thicknesses are experimentally investigated. The test bed is composed of an Inconel 718 pipe instrumented by strain gauges sensors. Measured strains lead to the tightening pressure thanks to the large elastic resistance of Inconel. Evolutions with temperature are recorded. A thermo-mechanical constitutive law, specific for , has been developed. It is based on the Mori-Tanaka scale transition technique by considering the precipitates as elastic-plastic inclusions embedded in the SMA matrix. Its behavior is described by the Chemisky, Duval et al. constitutive model. The elastic-plastic constitutive law for inclusion is a classical one proposed by Simo and Hughes. The resulting effective law is implemented, and validated in ABAQUS via UMAT subroutine. The developed approach is adopted for the simulation of the experimental tests on rings, and comparisons are performed.