Influence of heating and cooling rates and testing media on results of ASTM E3097 testing performed on NiTi wire

The ASTM E3097 standard for constant-force thermal cycling provides a useful framework for measuring properties of shape memory alloys relevant to actuation applications, namely transformation strains and transformation temperatures. Being a thermal cycling test method, the rate of the heating and cooling is an important consideration. The standard allows for operator discretion when selecting a heating and cooling rate for the test, provided that the specimen temperature is maintained uniformly within ±3°C throughout the course of the thermal cycling. However, it can be difficult to verify specimen temperature in-situ during testing of wire specimens. It is, therefore, especially important when testing wire for the test operator to understand the potential influence of heating and cooling rates on test results. This work will compare the results from ASTM E3097 tests performed on various wire diameters using different heating and cooling rates, as well as different testing media. Data will be presented and analyzed for trends. Resulting observations will be presented, as well as recommendations for best practices when performing E3097 testing on wire.