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 defo rmation stage on samples previously prestrained in compression along t he [312BAR] transversal axis. For various prestrain amplitudes, the me chanical behaviour and the associated crystallographic features have b een observed at both dislocation structure and slip and twin activity scales. They have then been analyzed with the help of qualitative nume rical simulations obtained from a code specifically written for the si ngle crystal plasticity and based on a dislocation description of (wor k) hardening.