Micromechamical Analysis for Hysteretic Behavior of Unidirectional TiNi SMA Fiber Composites

Mechanical behavior of a unidirectional TiNi shape memory alloy (SMA) fiber composite subjected to a single isothermal loading and unloading cycle is analyzed using a threedimensional micromechanical method of cells. The multiaxial rhombohedral and martensitic phase transformations of TiNi SMA fibers embedded in an elastic matrix are taken into account. Numerical simulations are performed for different fiber volume fractions and for different fiber orientation angles. It is clearly observed that a pseudoelasticity-like hysteretic behavior appears in the stress-strain relationships of the composite system of TiNi SMA fibers and an elastic matrix under the prescribed isothermal loading and unloading conditions. The shape and size of the hysteresis are significantly influenced by the volume fraction of TiNi SMA fibers. For a high volume fraction of fibers, in particular, the rhombohedral transformation of the embedded TiNi SMA fibers characterizes the overall hysteretic behavior of the TiNi SMA composite. The present simulations manifest the significance of the capability to predict the rhombohedral transformation of TiNi SMAs under multiaxial loading conditions, and also demonstrate the efficiency of the micromechanical composite model for evaluating the average characteristics of the TiNi SMA fiber composites.