The early stages of plastic flow and micro-creep were studied in single crystals and in polycrystalline copper and aluminum using a method with a strain sensitivity of 2 x 10−6 at -196 to 25C. The temperature dependence of the 10−6 yield stress was interpreted as arising from a thermal activation of stacking faults under stress. This model resulted in a value of 25mJ/m2 for the stacking fault energy of copper and 100mJ/m2 for aluminum.

Initial Stages of Plastic Deformation in Copper and Aluminium. A.R.Rosenfield, B.L.Averbach: Acta Metallurgica, 1960, 8[9], 624-9