Study of phase transformation intermittency in S.M.A. using the grid method

We show experimentally the intermittency of the phase transformation in a shape memory alloy using a kinematical full-field measurement method. The specimen is a Cu-Al-Be single crystal with Ms = −2 °C. A uniaxial loading was applied by using a device based on gravity. In practice, a drop-by-drop device controlled by water pumps enabled us to apply a perfectly monotonic loading with very small force increments. The grid method was used to measure the strain fields on the specimen surface during the test. It is observed that the plateau which is classically obtained when the specimen transforms from austenite to martensite is actually characterized by an intermittency of the phase change. It means that the events, in terms of appearance of martensite needles and propagation, occur with an irregular alternation. The paper presents the experimental setup, the image processing and some typical results.