Effect of vacuum on fatigue fracture development in iron at various deformation amplitudes

Abstract

1. In the cyclic deformation of iron in the high-amplitude region, vacuum retards the formation of microcracks and their propagation evenly over the whole extent of the process to fracture. 2. When iron is loaded in the low-amplitude region, vacuum retards the process of fatigue fracture in all stages, especially in the stage of slow crack growth. 3. Fatigue microcracks appear in iron in the whole range of deformations after about 10% of the life of the testpiece; the stage of crack growth accounts for the main part of testpiece life both in air and in vacuo. The increase in the life of iron in vacuo by comparison with its life under atmospheric conditions at all the deformations studied is determined principally by the reduction in the speed of fatigue crack growth. 4. The slowing down in crack growth due to the effect of vacuum is apparently a result of reduction in the density of dislocations at the tip of the propagating crack, caused by the emergence of dislocations being eased by the reduction in the oxidation of the fresh surfaces.