Effective properties of a piezocomposite containing shape memory alloy and inert inclusions

We use the energy equivalence principle and the Mori-Tanaka method of considering the interaction among inclusions to derive the effective thermo-electro-mechanical properties of a 4-phase composite consisting of an elastic matrix and shape memory alloy, piezoelectric and inert (nonpiezoelectric) inclusions. It is shown that the shapes and the volume fraction of inert (e.g. air) inclusions significantly influence the effective properties of the composite, and the addition of soft inert inclusions decreases the axial stress required to initiate the phase transformation in the SMA inclusions, and increases the electromechanical coupling constant. The 4-phase composite makes a very good sensor to measure low values of the applied axial stress since the axial strain induced by an axial stress of 80 MPa is 2%, and the sensitivity of the sensor is improved by the addition of soft spherical inert inclusions. With a suitable choice of the matrix material, its compliance can be adjusted and its shape made to conform to that of the host structure.