Evaluation of static and dynamic fracture toughness using apparent fracture toughness of notched specimen

In this study, intrinsic static/dynamic fracture toughness of Al 7175-T74 and 17-4PH casting steel are evaluated from the apparent static/dynamic fracture toughness of notched specimen. Fracture toughness tests are conducted using an instrumented impact and three-point bending testers. The critical average stress fracture model is used to establish the relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched-cracked specimen. The critical average stress fracture model is suggested using the relationship between the notch root radius and the effective distance calculated by FE analysis. The results show that fracture toughness decreases as the notch root radius decreases until a limiting of critical radius. However, fracture toughness is independent of notch root radius below the limiting critical notch root radius. It is concluded that the true fracture toughness can be predicted from test results of apparent fracture toughness measured by using a notched specimen. Also, with the critical average stress fracture model, the equation predicting relation of notch root radius and apparent fracture toughness can be calculated.