Can the finite fracture mechanics coupled criterion be applied to V-notch tips of a quasi-brittle steel alloy?

Structures made of steel alloys with V-notches may fracture at the V-notch tip at which a small plastic zone usually evolves. Failure criteria for predicting fracture loads for such quasi-brittle alloys, as a function of the V-notch opening angle are very scarce and have not been validated, to the best of our knowledge, by a set of experimental observations. Herein we provide a database of experiments performed on AISI 4340 steel alloy specimens with three different V-notch opening angles and three different tempering temperatures, loaded in mode I. Material properties, failure load and plastic area at the V-notch tip are detailed. The experimental observations are used to investigate to which extent the finite fracture mechanics coupled criterion (FFMCC) for brittle materials may predict the failure load of quasi-brittle steel alloys, depending on the plastic zone size. Finite element analyses were used to compute the parameters required by the FFMCC. We compared the predicted versus the experimental fracture load for the different V-notch opening angles and tempering temperatures. For small opening angles (30°) for which the plastic area is very small, the FFMCC under-predicts the fracture load by about 20% which is within the experimental error range. The under-prediction of the failure load constantly increases to ∼ 50% as the V-notch angle increases to 90° and plastic zone area on the surface increases to ∼0.5mm² (for a V-notch depth of 5 mm). The detailed experimental database is suggested to be used for validation purposes when new failure criteria for quasi-brittle materials are developed.