Modification of texture by fatigue and its application to fatigue metering

Abstract

Soft aluminium foils, adhesively bonded to aluminium-alloy and steel specimens, were examined after fatigue testing to assess their damage as a measure of damage in the substrate. The intensity of the 511,333 X-ray diffraction line increased progressively with the number of fatigue cycles, confirming Japanese observations. Experiments show this increase to arise because the foil texture is modified by fatigue deformation. A limited correlation was found between fatigue cycles and integrated intensity for the case of fully reversed strain cycles, confirming the feasibility of using the phenomenon for monitoring fatigue deformation in a substrate. No texture changes could be detected, however, after repeated-tension loading. A novel technique is described for presenting information on texture changes; data for a reference foil were subtracted from data for a worked foil and the difference plotted using a modified pole-figure plotting program. Isometric plots of the crystalline density of the foils as a function of orientation were also of benefit in assessing texture changes.