X-ray Study on Fatigue Damage of Metallic Materials

Abstract

As the fatigue of metals is directly related with the variation of their crystal imperfection, X-ray method is the most adequate for the investigation of fatigue. In the present paper, the fatigue process is studied by observing the half-value breadth of intensity distribution curves taken from the X-ray patterns, which were obtained from the specimens of steel stressed by alternate torsion and rotary bending. It was found that during the fatigue process the change of half-value breadth was directly related with the change of micro-stresses. Results are obtained as follows : 1) The half-value breadth changes remarkedly with the repetition of stresses. 2) The change of half-value breadth complies with the mechanism of fatigue that consists of the accumlation of micro-stresses. 3) On a view of the half-value breadth variation during stress repetition, it is considered that the fatigue process consists of the three sequent stages which follows; a) A stage in which the half-value breadth changes markedly with stress repetition.-The primary stage of fatigue. b) A stage in which the half-value breadth changes steadily with stress repetition.-The secondary stage of fatigue. c) A stage in which the half-value breadth sharply varies until fracture occurs.-The tertiary stage of fatigue. 4) At the end of the secondary stage of fatigue, the half-value breadth has a constant value irrespective of the magnitude of alternate stresses. 5) The relation between b/B and log (n/N), where b and B are the current and the inintial value of half-value breadth, and n and N are the current and the ultimate number of stress repetition respectively, is represented by a straight line irrespective of magnitude of alternate stresses applied. This relation offers possibility of the non-destructive detection of fatigue damage.