X-Ray Investigation on the Fatigue Deformation in Aluminum

Abstract

Fatigue tests were undertaken on the base metals and welded joints of commercially pure aluminum. During the tests, X-ray differaction patterns were obtained for these specimens. Then the ratio of half-value breadth was examined for each specimen and also the diffraction patterns were Fourier-analysed to get the lattice strain and the apparent grain size. Conclusions obtained are as follows:
1. The change in the ratio of half-value breadth during the fatigue process was qualitatively the same as the change in the lattice strain obtained by Fourier-analysis of the diffraction patterns.
2. In the case of annealed specimen, the lattice strain increased initially and took a minimum value at about 0.25 of the ratio of cyclic number. Afterthat, it again increased linearly and the specimen fractured. This change in the lattice strain seems to be explained qualitatively by the change of microstructure obatined with electron microscope.
3. In the case of tensile strained and welded specimens, the lattice strain decreased while the apparent grain size increased. This means that the phenomenon of recovery occurred. Moreover, the lattice strains of all specimens have approximately shown the same value in fracture, though the initial conditions of the specimens were different.
4. It was confirmed that it would be possible to estimate the fatigue life by examining' the change in the ratio of half-value breadth.