実働荷重下のAl合金の疲労破面の電子顕微鏡による観察

抄録

Two kinds of fatigue tests were conducted, where two sinusoidal loadings were superimposed on each other, and where rectangular cyclic loadings were superimposed with sinusoidal loadings. The materials used were aluminum alloys, 17ST4 and 7075-T6. Those fracture surfaces were observed by means of an optical microscope and an electron microscope. Those observed patterns indicated the following striations; under constant amplitude loading cycles, the striations had even spaces within the glance area; under fluctuating load cycles, they had varied contrast and spaces, and presented clear periodicities corresponding to the load fluctuations. For example, in the case where 8 sinusoidal loadings were superimposed on each other in a rectangular wave cycle, 4 striations corresponding to σ_a+σ_mr were distinct, but 4 other striations corresponding to σ_a-σ_mr were feeble, where σ_a stood for the amplitude of sinusoidal stress cycle and σ_mr for the rectangular stress cycle. In consequence of those observations, it was clarified that the striations stood to the loading cycles as one to one, and that the maximum value of those striations and loadings stood each to each equally.