Evaluation of plastic geometry factors for SE(B) specimens based on three-dimensional finite element analyses

• Evaluate the plastic geometry factors for SE(B) specimens using 3D large-strain FEA.
• Evaluate the accuracy of the plastic geometry factors for SE(B) specimens in ASTM E1820.
• Investigate the impact of small-strain and large-strain formulations on the plastic geometry factors.
• Propose new expressions for the plastic geometry factors for SE(B) specimens.

The plastic geometry factors, i.e. the ηpl and γpl factors, are needed to calculate the J-integral from the load vs. crack mouth opening displacement (CMOD) or load-line displacement (LLD) curve in the J–R curve test. In this study, we carry out a systematic investigation of the ηpl factor for plane-sided and side-grooved SE(B) specimens with a wide range of crack depths (a/W ranging from 0.3 to 0.7) and thickness-to-width ratios (B/W equal to 0.5, 1 and 2) based on three-dimensional (3D) finite element analyses (FEA). To examine the accuracy of the ηpl factors suggested in ASTM E1820, the corresponding estimated J value are compared with the J value obtained from the 3D FEA based on both the large-strain and small-strain formulations. The LLD- and CMOD-based plastic ηpl factors corresponding to both the average J value over the crack front and the local J value at the mid-thickness of the crack front are evaluated. The main finding of this study is that besides the crack depth, both the thickness and side grooves of the specimens have observable impacts on the ηpl factor. Based on the results of the 3D large-strain FEA, a set of expressions for the ηpl and γpl factors are proposed. The results of this study can improve the accuracy of the experimentally determined J–R curve and facilitate the use of non-standard medium-cracked (0.3 ≤ a/W < 0.45) SE(B) specimens for the J–R curves testing.