Pseudoelastic behavior of a CuAlNi single crystal under uniaxial loading
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INTRODUCTION
STRESS-induced martensitic transformations have been studied in a number of alloys.[1–10] An important characteristic of shape-memory alloys (SMAs) is the ability to undergo a diffusionless, structural, and reversible martensitic phase transformation. The martensitic transformation is accompanied by a large shear-like deformation, which generally amounts to about 20 times more than the elastic deformation. The martensite may be induced from the parent phase either by loading or by cooling. Detailed investigations on thermoelastic martensitic transformation have been done in the fields of physics and materials science. A quite complete theoretical system, which includes the transformation crystallographic theory, thermodynamics, etc., has been established by Wechsler et al.,[1] Wayman,[2] Bowles and Mackenzie,[3] Delaey et al.,[4] Christian,[5] James,[6] Ball and James,[7] Bhattacharya,[8] Abeyaratne et al.,[9,10] and many others. On the other hand, with the increasing application of SMAs and structural ceramics, the study on the constitutive relation of the materials with thermoelastic martensitic transformation attracts the interest of researchers of solid mechanics. For example, much work has been done by Falk,[11] Patoor et al.,[12] Abeyaratne et al., Muller and Xu,[13] Chu and James,[14] Tanaka et al.,[15,16] Liang and Rogers,[17] Sun and Hwang,[18,19] Fischer et al.,[20,21] Yan et al.,[22,23,24] Chen et al.,[25] Song et al.,[26] Lu and Weng,[27] and many others. The pseudoelastic phenomena of SMA single crystals under uniaxial loading have been investigated by authors such as Okamoto et al.,[28] Horikawa et al.,[29] Shield,[30] and many others. It is generally believed that the shape strain defined by an invariant plane strain along a habit plane interacts with an applied stress, and, thus, a habit plane is selected by a DAI-NING FANG and KEH-CHIH HWANG, Professors, and WEI LU, Research Assistant, are with the Department of Engineering Mechanics, Tsinghua University, Beijing 100084, P.R. China. Manuscript submitted August 6, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS A
maximum Schmid factor for the shape strain.[30,31,32] In a series of articles, Ichinose, Otsuka, and Horikawa et al.[29,33] reported their research results of pseudoelastic phenomena of CuAlNi single crystals under uniaxial loading. Suezawa and Sumino[34] obtained the theoretical expression of the relation between the elastic constants of a CuAlNi single crystal and its orientations. However, there still remain some important problems regarding the orientation dependence. These include the selection of a habit plane variant under stress, the orientation dependence of transformation stress and strain, etc. For example, a systematic observation and recording of the microstructural changes during loading and unloading has always been a difficult problem which hampers us from a clear understanding of the process. The orientation dependence of critical stress is also an interesting subject. The purpose of the present article is to p
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