Mechanical Hysteresis in Deformed Copper Crystals

Half-cycle loops measured at room temperature in copper crystals of an easy glide strained into stage I represented decrements of the order of 10−1 at strain amplitudes in the 10−5 range. Coating the crystals with chromium was useful in extending the amplitude range over which closed loops could be studied. The energy loss was attributed to unpinning of primary-dislocation-forest-dislocation interactions. The large modulus reduction could be accounted for by using the density of excess primary dislocations inferred from pertinent etch-pit studies.