Abstract
Three-dimensional observations were made on the sizes and shapes of plastic zones formed around fatigue cracks in an Fe-3%Si alloy by means of the etch-pit method. Main results obtained are as follows:
(1) The shape and size of a plastic zone observed on the specimen surface are different from those in the interior, reflecting the change in the mode of deformation from “plane-stress” at the surface to “plane-strain” in the interior.
(2) The relationship experimentally obtained among plastic zone size, crack length and stress amplitude is predicted well by B–C–S model modified for fatigue cracks by taking the expedient cyclic yield stress into account.
(3) The stress state near the tip of a fatigue crack is assessed from measurements of the size of plastic zone on the specimen surface.
