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A study was made of the influence of grain size on the propagation of fatigue cracks in electrolytic tough pitch copper. Copper specimens possessing grain sizes ranging from 0.060 to 7 mm were produced by annealing at various temperatures for preselected periods of time. Center-notched specimens were subjected to a positive mean stress and an alternating stress superimposed. Measurements of crack length were taken continually throughout the test to determine fatigue crack length as a function of number of cycles. Observations were made, using optical and electron fractography, on the mode of propagation and the influence of grain boundaries on the crack as it extends through the matrix. At a given stress level the initiation period of a fatigue crack at the starter notch was observed to increase with decreasing grain size. However, grain size was observed to have little effect on the propagation rate.
copper, fatigue (materials), crack propagation, grain size, grain boundary, microstructure
Hoeppner, D. W.
Research metallurgistPersonal member ASTM, Battelle Memorial Inst., Columbus, Ohio