The Application of a Nonlinear Fracture Mechanics Parameter to Ductile Fatigue Crack Growth.

摘要

This report describes the methodology for predicting fatigue crack growth rate response of cracked structural components wherein the assumptions of linear elastic fracture mechanics are violated. Fatigue crack growth rate tests were conducted on copper specimens using compact tension (CT), centercracked panel (CCP), and radial-hole cracked (RHC) geometries. The CT and CCP specimens provided baseline fatigue crack growth rate data that were utilized to predict both the fatigue crack growth rate and the crack growth life behavior of the RHC test specimens. The nonlinear fracture mechanics parameter chosen for extensive study on this program was the J-Integral. Crack growth rate correlations were based on J max, i.e., the J-Intetral evaluated at the maximum loading condition, rather than the more traditional delta J associated with the range of load. Three calculations of Jmax were made; two were based on numerical results, the other on experimental results. The numerical J max values were based on (a) the line integral calculated using nonlinear finite element results and (b) the Shih estimating scheme which assumes power law hardening behavior. The experimental Jmax values were based on the method for measuring the change in the potential energy of deformation using load displacement data recorded during a fatigue test.