The use of various crack depths (a) and crack-depth to specimen-width (a/W) ratios in laboratory tests to model flawed structural components has led to considerable interest in the role of both the crack depth (a) and the a/W ratio on fracture toughness. To investigate the separate roles of crack depth and the a/W ratio, three-dimensional elastic-plastic finite element analyses, (FEA) of square SE(B) specimens with a/W ratios ranging from 0.1 to 0.5 [crack depths ranging from 2.0 mm (0.08 in.) to 50.8 mm (2.0 in.)] have been conducted. The material properties used in this analysis were those for the material used in an experimental study conducted at the University of Kansas (KU) and Oak Ridge National Laboratory (ORNL). The specimen dimensions were chosen such that the results for specimens having a fixed crack depth and varying a/W ratios could be compared to the results for specimens with a fixed a/W ratio and varying crack depths.
The results of the experimental studies had indicated that both the crack depth and the a/W ratio each have a significant effect on the fracture toughness. Both the lower bound toughness and the transition temperature were affected. Three-dimensional elastic-plastic FEA were used to model each specimen geometry, and the predicted stresses, CTOD, and J-integral for the various crack depths and a/W ratios were compared. The results of the FEA support the findings of the previous experimental study. For a high-constraint geometry (a/W = 0.5), there is not a significant change in the near tip stresses for different size specimens. However, for low-constraint geometries (a/W = 0.1), the near tip stresses are significantly affected by the actual crack depth and specimen size. The findings of this study are significant in helping to understand the relative role of crack depth, a/W ratio, and specimen size on fracture toughness. Future studies are expected to extend the findings of this study to the behavior of actual structures with cracks.