Fracture Behavior Prediction for Rapidly Loaded Surface Cracked Specimens

The feasibility of predicting the fracture behavior of surface cracks from shallow cracked bend specimens was investigated. The material studied was a high-strength steel stress relief embrittled to various levels of Charpy-V notch impact toughness. Material toughness was quantified in terms of the J-intergral at total specimen failure (-/„,,), using both deeply notched and shallow-notched bend bars (single-edge notch bend) (SE(H)] dynamically loaded in a drop tower impact testing machine. These data were compared with the fracture behavior of rapidly pressure loaded part-through surface cracked bend [PS(B)] specimens, which had a shallow surface flaw introduced at the specimen midspan. For highly embrittled material (Charpy V-notch energy (CVE) between 10 J and 24 J), J^ values measured using shallow crack SE(B) specimens were consistently higher than deep crack ./„,, values due to the shorter crack size, as well as increased plastic energy dissipation within the specimen. These higher J^ values served as better predictors of the PS(B) fracture performance than did comparable deep crack values. Even though Jm cannot be considered a geometry independent measure of fracture toughness for shallow through cracks, values of this parameter determined using test specimens containing them appear to have considerable engineering utility for predicting the fracture behavior of part-through surface flaws.