ARTIFICIAL RETARDATION OF FATIGUE-CRACK GROWTH BY THE INFILTRATION OFCRACKS BY FOREIGN MATERIALS

The effects of inducing artificial crack closure into fatigue cracks i n AISI 304 stainless steel by infiltrating foreign materials have been investigated. The foreign materials used include pure epoxy resin and resin mixed with 0.3 mu m and 4 mu m TiO2, 4 mu m Fe, as well as 18 m u m AISI 316L stainless steel. In all the cases studied, different deg rees of crack growth retardation have been achieved. When the particle size was small enough or when the prop-opening load for infiltration was large enough, crack arrest occurred. Crack retardation and arrest were mainly caused by the infiltrated material rather than the proppin g load. A rigid-wedge model was found to have limited value in predict ing the possible outcome of an infiltration. On the other hand, the de gree of crack closure immediately on resumption of a test after infilt ration could tell whether the treatment was going to be successful or not.