Stress-induced acicular martensites in Cu-14.2Al-4.3Ni (wt %) alloy were investigated by means of transmission spear-like martensite thermally formed in the same alloy in several respects such as in shape, lattice invariant shear, habit plane and orientation relationship, even though both have the same crystal structure and lattice parameters. The lattice invariant strain of the martensite was found to be stacking faults on the basal plane, and a defectless region was observed at the middle of the martensite, which is in sharp contrast to the midribs in ferrous twinned martensites. The habit plane

Cyclic deformationand fatigue behavior of polycrystalline Cu-Al-Ni shape memory alloys above Ms point have been studied in a preceding paper (Trans. JIM, 27 (1986), 592), and the experimental results have been analyzed in the present paper. Almost all the experimental results, that is, extrapolation cracking (IGC) model previously proposed by the present authors (Trans. JIM, 23 (1982), 585). In the model, IGC has been elucidated to be due to a stress concentration effect caused by the transformation strain of stress-induced martensites along grain boundaries. The stress concentration effect in this model

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