INFLUENCE OF STRAIN-RATE ON DEFORMATION PROPERTIES OF TINI SHAPE-MEMORY ALLOY

Tensile tests with loading and unloading under various strain rates ep silon were performed for TiNi shape memory alloy wires at various cons tant temperatures. The influence of strain rate on the stress-strain-t emperature relationship was investigated. The main results are summari zed as follows. (1) For epsilon<10%/min, the martensitic transformatio n stress and its reverse transformation stress did not depend on epsil on. These stresses were almost constant in the transformation regions. (2) For epsilon greater than or equal to 10 %/min, the martensitic tr ansformation stress increased and its reverse transformation stress de creased with an increase in epsilon. These stresses fluctuated in the transformation regions. (3) The influence of epsilon on the transforma tion stress due to R-phase transformation was slight. (4) The recovera ble strain energy density depended slightly on epsilon but increased s ignificantly in proportion to temperature. The dissipated strain energ y density depended slightly on temperature but increased in proportion to epsilon for epsilon greater than or equal to 1 %/min. ( 5) The inf luence of epsilon on deformation properties is important in the evalua tion of mechanical properties of shape memory alloy elements.