Continuous Observations of the High-Temperature Fatigue in Pure Metals by means of the Microscopic Cine-Camera

Abstract

In order to study the high temperature fatigue mechanism in pure metals, an apparatus containing a microscopic cine-camera combined with the fatigue machine was devised for continuous and direct observations of the specimen surface during the fatigue in vacuum at elevated temperatures. A Xenon flash tube was used for illuminating the specimen surface. It was triggered synchronizingly at the same phase of deformation of the specimen. Each cut of the fatigue process was photographed in the time-lapse sequences and also taken in motion picture if necessary.The time-lapse technique was effective in analyzing the fatigue mechanism at elevated temperatures. The results obtained in the specimens of pure aluminum and lead under reversed bending and torsional stresses (1) The grain boundaries move in a way that they are in parallel with the maximum shear stress direction of the specimen axis. Accordingly, grain boundaries of polycrystals are gradually aligned orthogonally with the maximum shear stress direction during the fatigue.(2) Subgrains generate in coarsed grains or in single crystals under reversed stress, and their grain boundaries are aligned orthogonally as in the above case.(3) The surface markings consisting of a series of sharp valleys and peaks due to the deformation band (4) These continuous observations for the fatigue process serve to support the high-temperature fatigue mechanism which has been described in the previous reports.