ON THE TWINNING INITIATION CRITERION IN CU-AL ALPHA-SINGLE CRYSTALS .1. EXPERIMENTAL AND NUMERICAL-ANALYSIS OF SLIP AND DISLOCATION PATTERNS UP TO THE ONSET OF TWINNING

Tensile tests on Cu-Al alpha single crystals oriented along the [111] axis have been performed, at room temperature, up to the twinning deformation stage on samples previously prestrained in compression along the [312BAR] transversal axis. For various prestrain amplitudes, the mechanical behaviour and the associated crystallographic features have been observed at both dislocation structure and slip and twin activity scales. They have then been analyzed with the help of qualitative numerical simulations obtained from a code specifically written for the single crystal plasticity and based on a dislocation description of (work) hardening.