Sakae Takeuchi1 and Tsuneo Honma1
1The Research Institute for Iron, Steel and Other Metals, Tohoku University, Sendai
In order to investigate the mechanisms of fatigue at elevated temperatures, the processes of fatigue in annealed specimens of 99.99%Al and Pb were observed microscopically at testing temperatures from 0.5 to 0.85 Tm°K under reversed torsional or bending stresses.
The results observed at the early stage of the high temperature fatigue are summarized as follows:
(1) The grain boundaries move in parallel to the maximum shear stress direction of the specimen axis.
(2) Accordingly, grain boundaries of polycrystals are gradually migrated orthogonaly in the maximum shear stress directions under a reversed stress.
(3) The above characteristics of grain boundary migrations are observed not only at the surface, but also at the interior of the specimen.
The reasons for the above phenomena are discussed in connection with the release of the stored energy resulting from the boundary sliding in repetition, slips in the matrix along near the maximum shear stress direction and a small amount of the vacancy flow as compared with that of creep.
Please do not copy without permission.