Abstract
A method for automatic evaluation of fatigue striation was proposed. The principle of the method is consisted of one dimensional Fast Fourrier Transformation Analysis (FFTA) of image signal from the scanning electron microscope and easily accessible with personal computers. Fracture surfaces of steel, aluminium alloy and titanium alloy specimens were prepared by constant or variable amplitude fatigue tests and examined. For constant amplitude fatigue several peaks were revealed on the power spectre diagram by FFTA : the first corresponding to macroscopic inclination of the facet, the second representing the mean striation spacing and the third exhibiting more detailed structures or slip lines within the striation. For variable amplitude fatigue by block programmed cycling the power spectre diagram comprized many separate peaks in which the highest was found to represent the trace of crack propagation by one programme block. Striation spacing obtained from FFTA agreed well with results from direct measurement by conventional methods.
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