Small Angle X-Ray Scattering from Copper and Aluminum under Cyclic Stress

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Abstract
Copper and aluminum samples were subjected to cyclic stress and run to fatigue while being held in an x‐ray beam. Small angle scattering intensities were recorded at various stages of the fatigue life. These intensities were found to increase with the number of elapsed stress cycles. The observed angular dependence and intensity of the scattered radiation agrees most nearly with a double Bragg scattering mechanism. The relation of the fatigue mechanism to the formation of small angle subgrain boundaries responsible for the double Bragg scattering is not clear‐cut. However, the evidence favors the view that the formation of subgrains, while probably necessary to the propagation of the fatigue crack, is not sufficient either for its formation or propagation. Complete annealing of the scattering was not possible, indicating that recrystallization does not take place following cyclic stress of the order of one‐fourth the yield stress. No evidence exists for a widespread formation of voids in the fatigued specimen.