Abstract
An X-ray fractographic study was made on the fatigue fracture surface of SM50A and HT80 steels. The residual stress and the half-value breadth of X-ray diffraction profile were measured at and beneath the fracture surface. The correlation was examined between the parameters obtained from the X-ray measurements and the fracture mechanics parameter of Kmax or ΔK at which the fracture surface had formed.
The residual stress on the fracture surface was found to increase at first, reach to a maximum value at a certain value of Kmax or ΔK and then decrease. It was also found that the residual stress was controlled by Kmax in a low Kmax or ΔK region, while it was governed by ΔK in a high Kmax or ΔK region. The reasons of this behavior were discussed by using the data from constant Kmax and constant ΔK tests which were additionally planned and made in this study. The half-value breadth, B, on the fracture surface was found to increase with Kmax in the two steels used in this study. The value of B was influenced by stress ratio in HT80, although it was not influenced in SM50A. Both of the distributions of residual stress and half-value breadth beneath the fracture surface were found to be useful for the prediction of monotonic plastic zone size or Kmax.
