Dauphine twinning and texture memory in polycrystalline quartz

Mechanical twinning in polycrystalline quartz was investigated in situ with time-of-flight neutron diffraction and a strain diffractometer. Dauphine twinning is highly temperature sensitive. It initiates at a macroscopic differential stress of 50-100 MPa and, at 500 degrees C, saturates at 400 MPa. From normalized diffraction intensities the patterns of preferred orientation (or texture) can be inferred. They indicate a partial reversal of twinning during unloading. The remaining twins impose residual stresses corresponding to elastic strains of 300-400 microstrain. Progressive twinning on loading and reversal during unloading, as well as the temperature dependence, can be reproduced with finite element model simulations.