Mechanical Properties of Elastocaloric Materials

Assessment of mechanical properties and superelastic behavior is a major expertise at the University of Maryland (UMD).

One of the hallmarks of the elastocaloric effect is the superelastic behavior of shape memory alloys. When the stress-induced superelastic transition takes place, latent heat is released, and the austenite becomes a martensite. In the reverse step of the superelastic transition, the martensite transforms back to austenite upon unloading of the stress and latent heat is now absorbed from the environment as the elastocaloric cooling effect.

One ongoing challenge with elastocaloric materials is their relatively large critical stress where superelasticity commences. For instance, the critical stress for a typical NiTi in compression is more than 600 MPa. As we develop new elastocaloric materials, it is crucial that we monitor how the critical stress changes for different materials. For this purpose, characterization of mechanical properties (e.g. stress-strain curves) of shape memory alloys is critical.

At UMD’s Mechanical Properties Lab, there are 2 MTS 810 Systems. One has 250 kN capacity and the other has 100 kN capacity to measure mechanical stress and strain of bulk materials. The auxiliary annular furnace allows a sustained temperature up to 1200°C to measure temperature-dependent stress-strain behavior of bulk materials.