Abstract: TO investigate the difference in fatigue behavior between single- and poly-crystals, it is necessary to reveal the fatigue damage mechanism of bi-crystals. Recent research progress in fatigue behavior of copper bi-crystals with different component crystals and grain boundaries was summarized. A model of grain boundary strengthening in copper bicrystals with parallel grain boundaries induced by the cyclic deformation was proposed by using the concept of Schmid factor and the grain boundary affected zone. By ...