Abstract
The X-ray diffraction method was used to observe the material substructure due to plastic deformation near the fatigue fracture surface of low-carbon steel. The fracture surface was made under a stress-intensity-factor controlled condition by using a computer-controlled servo-hydraulic fatigue testing machine. The distribution of the half-value breadth of the diffraction profile beneath the fracture surface was determined. The half-value breadth took the maximum value at the border of reversed plastic zone, while it approached to the initial (pre-fatigue) value near the boundary of the monotonic plastic zone. Microstructural parameters derived from computer image analysis of X-ray microbeam patterns were also usable to determine the sizes of the reversed and monotonic plastic zones. The distributions of X-ray parameters in the monotonic plastic zone were controlled by the maximum stress intensity factor, and those in the reversed plastic zone by the range of the stress intensity factor.
