Hybrid Shape Memory Alloy Composites for Extreme Environments.

摘要

The capability of Shape Memory Alloys (SMAs) to generate a residual stress state in a new hybrid SMA-ceramic composite for extreme environments is explored here. By generating a compressive residual stress on the ceramic phase, the beneficial material response observed under compression may be utilized. Specifically a SMA-MAX phase composite with a heterogeneous, irregular microstructure is considered. To incorporate the effects of the microstructure, a numerical model of a realistic microstructure is generated through the results of x-ray tomography and converted into a Finite Element (FE) mesh. A recent phenomenological model for the constitutive behavior of SMAs is then used to describe the response of that phase while an elastic-plastic approximation is used for the MAX phase behavior. The composite is subjected to an actuation (isobaric) loading path. It is shown that through such a loading path, martensitic transformation generates irrecoverable strains in the ceramic phase which results in compressive residual stress state upon unloading. By comparing with the results of a purely thermal or mechanical loading path, the necessity of using SMA transformation through a thermomechanical loading path is demonstrated.