ANALYSIS OF STRESS INTENSITY FACTORS FOR SURFACE CRACKS SUBJECTED TO ARBITRARILY DISTRIBUTED STRESSES.

Abstract

An influence function method has been developed to analyze effectively the stress intensity factor, K, for surface cracks subjected to arbitrarily distributed surface stresses. The method is based upon the superposition of the 'unit distributed load' at each nodal point on the cracked surface. It can be easily incorporated with the ordinary three dimensional finite element code which utilyzes the 20-noded isoparameteric elements with quadratic shape functions. A series of influence coefficients, K//i//j, have been calculated for flat plates with a semielliptical and a quarter-elliptical surface crack of various aspect ratio, a/c, and depth to thickness ratio, a/t. It has been shown, based upon the data of K//i//j, how easily the K-values for a surface crack with arbitrary values of a/c and a/t can be evaluated against arbitrarily distributed stresses such as residual stress and unsteady thermal stress.