Effects of graphite shape, size and distribution on the fatigue strength of spheroidal graphite cast irons

Abstract

Spheroidal graphite (SG) cast iron is a typical porous material which contains numerous small defects (graphites) in the matrix. In order to clarify the geometrical parameter for the quantitative evaluation of the effect of surface graphite on the fatigue strength of SG cast iron, rotating bending fatigue tests were carried out on the plain- and notched-specimens of as-cast FCD60 and FCD70. It is concluded from the microscopic observation that the fatigue limit is controlled by the maximum size of surface graphite defined by the square root of the projected area of graphite (√area*max). The value of √area*max in a definite surface area of the specimen can be predicted by the statistics of extreme values. The predicted values of √area*max approximately agree with the critical size of artificial notch which does not act to reduce the fatigue strength. The value √area*max is in general considered to be the controlling geometrical parameter for the prediction of fatigue strength of porous materials. © 1989, The Society of Materials Science, Japan. All rights reserved.