Compressive surface strengthening of brittle materials

A theoretical approach has been put forward for predicting the strengthening of materials by the introduction of surface compressive stresses. An approximate technique was used to determine the closure length of a linear surface crack which extends through the compressive surface layer. The stress intensity factor of the partially closed crack was then determined for the case of an applied tensile stress, with the assumption that the residual surface compressive stress was uniform within the surface layer (step function). The analysis shows that the strengthening depends on the magnitude and depth of the compressive surface stress. It is found that partial crack closure decreases the amount of strengthening compared with that predicted for an open crack, and that for large compressive surface stresses the amount of strengthening can saturate.