Modeling of transformation-induced plasticity and its effect on the behavior of porous shape memory alloys. Part II: porous SMA response

Abstract The thermomechanical constitutive model for fully dense shape memory alloys (SMAs) developed in Part I [D.C. Lagoudas, P.B. Entchev, to be published. Modeling of transformation-induced plasticity and its effect on the behavior of porous shape memory alloys. Part I: constitutive model for fully dense SMAs, Mechanics of Materials, this issue] of this two-paper series is used in a micromechanical averaging scheme to establish a model for the effective mechanical behavior of porous shape memory alloys. An incremental formulation of the Mori–Tanaka averaging scheme is employed in this work, where the porous material is treated as a two-phase composite with an SMA matrix and the pores as the second phase. The simultaneous development of transformation and plastic strain in the SMA matrix is taken into account. Expressions for the effective elastic and tangent stiffness tensors are presented as well as an expression for the evolution of the effective inelastic strain. The material parameters used by the model are estimated for the case of porous NiTi SMA processed from elemental Ni and Ti powders. Two different porous NiTi alloys are considered in the current work––material with large pore size (∼1 mm) and with small pore size (∼25 μm). The results of the model simulations for compressive mechanical loading of both types of porous SMAs are compared with the experimental data.

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