MULTIVARIANT MODEL FOR SINGLE-CRYSTAL SHAPE-MEMORY ALLOY BEHAVIOR

A general 3-D multivariant model based on thermodynamics and micromech anics for single crystal shape memory alloy (SMA) behavior is presente d. This model is based on the habit plane and transformation direction s for the variants of martensite in a given material. From this inform ation, the single crystal behavior of the material to temperature and mechanical loads is derived using the concept of a thermodynamic drivi ng force. The Eshelby-Kroner approach is utilized to determine the int eraction energy between the variants, where it is assumed that variant s can be subdivided into several self-accommodating groups in which va riants can grow together compatibly. This model is examined initially for a simple 2-variant case and then extended to the typical 24 varian t case. The multivariant model is shown to exhibit appropriate respons es for uniaxial results on single crystals: the transformations occur instantaneously when the critical stress/temperature is reached; both pseudoelasticity and the shape memory effect are captured. The model i s also examined for responses to multiaxial loadings and the distincti on between perfectly compatible and imperfectly compatible variants (w ith nonzero volumetric transformation strain) is discussed. (C) 1998 E lsevier Science Ltd. All rights reserved.