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Polycrystalline specimens of copper, aluminium and gold were fatigued in, reversed bend in various pressures of air and in water vapour and inert gases. The ratio of life in atmosphere of air 60 that. in vacuum (∼ 10-6 mm Hg) at lives of about 106 cycles was 1:20 for copper, 1:5 for aluminium and about 1:1 for gold.Some specimens were examined at intervals during the test. Small cracks a few microns deep formed in the first few hundredths of the life in air and after the same number of cycles in vacuum. The effect of air was to speed the propagation of cracks in copper and aluminium but not gold.Electron micrographs showed that extrusions and intrusions can occur close to each other in the same slip band.

Copper single crystals were strained cyclically with a plastic tensile strain amplitude of 0.5%. The variation of flow stress with strain rate and temperature was measured. Comparison measurements were made on specimens strained unidirectionally in the same apparatus. The variation of flow stress with temperature was considerably larger for the cyclically strained specimens than for the unidirectionally strained ones. The variation with strain rate was slightly larger. It is concluded that the frequency factor of the thermally activated rate-controlling process is considerably higher in the cyclically strained specimens.Considerable long-range internal stresses were present. They appeared to be a larger fraction of the applied stress in the unidirectional tests.