# Superelasticity in Shape Memory Alloys—Experimental and Numerical Investigations of the Clamping Effect

## TL;DR

This study explores how different clamping methods affect the superelastic behavior of shape memory alloys during tensile tests.

## Contribution

The authors developed a new bollard grip to reduce stress concentration and studied its impact on phase transformations in shape memory alloys.

## Key findings

- The bollard grip reduced local stress concentration in shape memory alloy specimens.
- Martensitic transformation and stress–strain plateau were observed during tensile tests.
- Numerical simulations matched experimental results, confirming the influence of clamping on phase changes.

## Abstract

Loading and clamping schemes significantly influence the behavior of shape memory alloys, specifically, the course of their solid-state transformations. This paper presents experimental and numerical findings regarding the nonlinear response of samples of the above-mentioned type of smart materials observed during tensile tests. Hysteretic properties were studied to elucidate the superelastic behavior of the tested and modeled samples. The conducted tensile tests considered two configurations of grips, i.e., the standard one, where the jaws transversely clamp a specimen, and the customized bollard grip solution, which the authors developed to reduce local stress concentration in a specimen. The characteristic impact of the boundary conditions on the solid phase transformation in shape memory alloys, present due to the specific clamping scheme, was studied using a thermal camera and extensometer. Martensitic transformation and the plateau region in the nonlinear stress–strain characteristics were observed. The results of the numerical simulation converged to the experimental outcomes. This study explains the complex nature of the phase changes in shape memory alloys under specific boundary conditions induced by a given clamping scheme. In particular, variation in the martensitic transformation course is identified as resulting from the stress distribution observed in the specimen’s clamping area.