Stress Induced Martensitic Transformation in Shape Memory Alloys Studied by In-Situ Neutron Diffraction Techniques

Shape memory alloy (SMA) elements are being embedded in smart materials and hybrid composites as actuating and/or sensing elements responding to the stress and temperature stimuli. In order to design smart composites, in-situ experimental information about evolution of internal stresses and phase fractions in the embedded SMA elements and internal stresses in neighboring matrix during actuation cycles would be of interest. Such experimental data have to be obtained nondestructively from the microscopic particles or fibres deep in the bulk specimens exposed to stress and/or thermal variations. In-situ neutron diffraction experimental techniques fulfill in principle these requirements. However, reliable evaluation of internal stresses from neutron diffraction experiments in the smart SMA composites can be made only after the lattice plane responses of monolithic SMAs in thermomechanical cyclic loads are fully understood. In this paper, the results of the in-situ investigations of stress induced martensitic transformation (SIMT) in tensile tests carried out on monolithic CuAlZnMn SMA polycrystal are reported, and the observed lattice plane responses are interpreted using a selfconsistent model of SMA polycrystal.