From the lattice measurements of the austenite and the martensite cells tothe macroscopic mechanical behavior of shape memory alloys

On one hand, the lattice measurements of the austenite and the martensite c ells for one CuZnAl and one CuAlBe alloys permit to determine the nature of the phase transformation i.e. an "exact" interface between the parent phas e and an untwinned martensite variant. Hence, for single crystals, the yield surface looks like a polygon with sev eral sectors. Each sector is defined by its peculiar activated variant. On the other hand, a "micro-macro" integration allows to predict the yield curve for biaxial proportional mechanical tests on polycrystals. This homog enisation process is in agreement with the prediction of a phenomenological approach at the macroscopic scale and fits well the yield experimental poi nts.