The Low-Cycle Fatigue Behaviour of Copper at Elevated Temperatures

Tensile and high-strain fatigue tests have been carried out at elevated temperatures on specimens of oxygen-free, high-conductivity copper and vacuum-cast copper. Grain-boundary sliding and grain-boundary migration occur during testing to produce boundaries orientated preferentially at ∼ 45° to the stress axis. In oxygen-free, high-conductivity copper, cracking takes place at triple points as a result of stress concentrations induced by sliding. The cracks increase in length with further fatigue and eventually link together by ductile rupture to cause final failure. With vacuum-cast copper, triplepoint cracking is suppressed owing to the greater mobility of the grain boundaries and failure in tension and fatigue is due to rupture following plastic instability.