An X-Ray Study of the Changes that Occur in Malleable Iron During the Process of Fatiguing

Abstract

Carefully prepared test bars of malleable iron have been fatigued; x-ray diffraction patterns were taken of each specimen at intervals as fatiguing progressed. This study shows that, when malleable iron is fatigued below its endurance limit, no changes in internal structure that are detectable by the camera used occur after the first few cycles. However, when malleable iron is fatigued above its endurance limit, marked changes do occur. Appreciable changes may occur during the first few cycles of fatiguing. Changes then take place comparatively slowly during the major part of the fatiguing process. These changes proceed at an accelerated rate as the specimen approaches failure. The changes consist of (1) rotation of some of the grains, (2) introduction of strains in some of them, and (3) fragmentation of some of the grains into sizes small enough so that they arrange themselves with random orientation. These changes are all readily detectable with the camera used.