Pull-Out Testing of Electrochemically Etched NiTi Shape Memory Alloy Wires in Shape Memory Alloy Hybrid Composites

This study presents an experimental characterization of the interface strength of the shape memory alloy hybrid composite (SMAHC) consisting of the two-way effect NiTi shape memory alloy (SMA) wire structured by electrochemical etching and the surrounding thermoset matrix. Mechanically induced, in situ thermally induced, and cyclic load-increase pull-out tests consistently reveal that SMAHC with structured SMA wires outperforms those with as-delivered SMA wires by a substantial factor of 2.6-2.7 in interfacial strength - the critical factor governing the overall performance and functionality of the composite. Analyzing the force-displacement curves from mechanically induced pull-out tests demonstrates that structuring the SMA wire surface leads to a significantly increased elastic energy to initiate a crack and achieve complete failure. SMA wires with structured surfaces continue transferring load even after the initial interfacial failure due to the presence of intact mechanical interlocking sites. The cyclic load-increase pull-out test confirms that SMA wires with structured surfaces exhibit a significantly higher load-bearing capacity, withstanding more load levels and demonstrating greater force of the first failure. Furthermore, in thermally induced pull-out tests with structured SMA wires, a re-initiation of failure from the lower side follows an initial failure progression at the SMA wire entry point. This study assesses the interfacial strength of a shape memory alloy hybrid composite comprising a two-way shape memory effect NiTi wire structured through electrochemical etching and a thermoset matrix. Beyond the conventional mechanically induced pull-out test, the research introduces two further pull-out tests: the in situ thermally induced and cyclic load-increase pull-out tests, simulating real operational conditions more closely.image (c) 2024 WILEY-VCH GmbH