Prediction of crack opening stress for part-through cracks and its verification using a modified strip-yield model

Abstract

Newman's crack opening stress equation [Newman JC. Jr. A crack opening stress equation for fatigue crack growth. Int. J. Fract. 1984;24:R131-R135.] was extended to predict the crack opening stress of part-through cracks within a finite body. The extended equation was obtained by replacing the normalized maximum applied stress S-max/sigma(0) as the normalized stress intensity factor (SIF) K-max/K-0, where K-max is the SIF including the geometry correction factor F, and K-0 is the stress intensity factor for flow stress. In order to verify the crack opening stress obtained from the extended equation, the modified strip-yield model using a slice synthesis technique [Daniewicz SR. A modified strip-yield model for prediction of plasticity-induced closure in surface flaws. Fatigue Fract. Engng. Mater. Struct. 1998;21:885-901.] was utilized and the approximate weight function was modified to consider the effect of the restraint due to the uncracked area. For a corner crack or surface crack within a finite body, the crack opening stresses obtained from this model were correlated well with the results of the extended equation. Additionally, the crack shape evolutions of surface crack subjected to uniaxial constant amplitude loading or four-point bending loading were predicted by the extended crack opening stress equation and compared with experimental data for aluminium alloy specimens with R = 0.1, The predictions were in good agreements with experimental data. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.