ESTIMATION OF BRIDGING INTERACTIONS FOR NATURAL CRACKS FROM BENDING STRENGTH OF COARSE-GRAINED AL2O3

Several ceramic materials show R-curve effects which in the past were investigated mainly with specimens containing artificial macrocracks. This paper describes how the R-curve effects caused by bridging interactions between the crack surfaces will influence the strength of specimens with natural crack populations, Calculations in terms of averaged stress intensity factors were performed to describe the development of surface cracks from the initial size up to the size at failure. As a consequence of bridging interactions, deviations from the expected straight line in the Weibull representation of strength will occur even under the assumption that the initial crack size is Weibull-distributed. A least-squares procedure allows the bridging stresses to be estimated from bending strength measurements.