Effect of Crack‐Interface Bridging on Subcritical Crack Growth in Ferrites

Abstract

A transition between transgranular fracture and intergranular fracture in polycrystalline manganese zinc ferrites has been investigated by measuring subcritical crack growth in double‐cantilever‐beam specimens. Log velocity vs K 1 plots are like those for other ceramic materials with three well‐defined regions of growth. Unlike other ceramics, however, the K 1 values at which crack growth became critical showed large variations with relative humidity. Crack velocities depended on prior history and, at K 1 > 1.1 MPa · m 1/2 in dry N 2 , crack growth was intermittent. All of these features were related to an increase in intergranular fracture with K 1 . A model is presented to explain the data in terms of the generation ad removal of crack‐interface bridges which were produced by intergranular fracture.