QUANTITATIVE EVALUATION OF ELECTRON-FRACTOGRAPHY OF FATIGUE FRACTURE SURFACE.

In exploratory investigations of the possibilities of using electron fractography as a means of analyzing fatigue failures, fatigue fracture surfaces of aluminum alloys, titanium alloys, and ultrahigh strength steel were studied. The spacing of striations which are characteristic of fatigue fracture surfaces was related to the crack tip stress intensity factor. Using the relation between stress intensity factor and depth of plastically deformed layer along the fracture surface measured by x-ray diffraction, applied stress conditions could be estimated. It is pointed out that caution must be used in applying the method to high strength steel because the relation between striation spacing and crack growth rate was found to be affected by the fracture toughness of the material.