Effect of Crack Front Curvature on Experimental Evaluation of J-Integral for Single-Edge Bend Specimens

摘要

This paper presents three-dimensional (3D) finite element analyses of plane-sided single-edge bend specimens to investigate the effect of the crack front curvature on the accuracy of the average J-integral (J) evaluated over the crack front using the plastic eta-factor-based approach specified in ASTM E1820-11. Specimens with average crack lengths of 0.3, 0.5, and 0.7 and thickness-to-width ratios of 1, 0.5, and 0.25 were analyzed. The analysis was based on the J_2 deformation theory of plasticity and assumed stationary cracks with sharp crack tips. The curved crack front was characterized by a power-law expression proposed by Nikishikov et al. that was validated using crack front data collected in this study. The plastic eta factors specified in ASTM E1820-11 and proposed by Zhu et al. were employed. The analysis results indicate that the errors in the plastic eta-factor-based J were generally between -7 % (i.e., underestimation) and 6 % (i.e., overestimation) for the specimens that had curved crack fronts with crack front curvature equal to the maximum allowable value specified in ASTM E1820-11. Based on the analysis results, crack front straightness criteria that are in most cases less stringent than those specified in ASTM E1820-11 are recommended. The suggested criteria could potentially lead to reduced specimen rejection rates and cost savings.