Characterization of crack-tip fields for elastoplastic fatigue crack growth Part II: Effects of crack closure and in-plane constraint

The crack-tip fields of elastoplastic fatigue crack growth with crack closure are studied and correlated to the Delta J-integral. Computational results confirmed that the singularity of the effective stress ranges of the opening process reduces with increasing crack closure, whereas the effective stress ranges from the closing process possess the known HRR solution form. The farfield Delta J(eff)-integral can be used to characterize the crack-tip field stress in the closing process, which is not affected by the loading ratio and by the path dependence of the Delta J-integral. Based on extensive FEM computations, an estimation formula for the effective Delta J(eff) -integral was proposed for various loading ratios and plastic hardening materials. The in-plane constraint effects in fatigue crack growth can be quantified based on the J - Q concept of elastoplastic fracture mechanics, within the frame of Delta J(eff) -Q characterization. The relationship between.. and the transverse stress defined in the closing processes was established for a quantitative description of the crack tip constraint.