Fracture toughness prediction of low alloy steel as a function of specimen notch root radius and size constraints

The effect of specimen notch root radius rho and specimen size (thickness B and ligament b) on the apparent fracture toughness K-I,K-app is investigated. Series of fracture tests on nonstandard compact tension CT specimen of low alloy steel EN34NiCrMo6, which is equivalent to AISI 4340 low alloy steel with different values of rho and crack length to width ratio a/W were conducted to measure the K-I,K-app. The experimental results show that, K-I,K-app depends on rho and specimen size. There is a critical notch root radius rho(c) under which K-I,K-app becomes independent of rho. Two empirical models have been proposed to predict K-I,K-app and can be used to transfer the data among specimens of different rho. One additional empirical model is developed to transfer the data among specimens of different ligament, b. Finally, a model is developed by modifying the ASTM E1921 standard equation (which predicts the thickness effect only) to include the combined effect of B and b. The model predictions are in good agreement with the experimental results. (C) 2012 Elsevier Ltd. All rights reserved.