Microstructural evaluation of cumulative fatigue damage below the fatigue limit

摘要

The objective of this work is to evaluate the m ierostructural changes induced near and below the fatigue limit in a pressure vessel steel plate, SA508. Dislocation cell to cell misorientation differences, 6, which increase with fatigue damage accumulation, arc measured by the Selected Area Diffraction (SAD) method. The misorientation difference, 0, of the sample failed just above (lie fatigue limit is about 40 degrees on the average, which is about the same as that for the failure conditions of low cycle fatigue at higher stresses. ThcO value increases even below the fatigue limit, but it does not increase at stresses which are lower man 50% of the fatigue limit.