Predicting failure initiation at V-notch tips in an AISI 4340 alloy by a continuum damage model

Predicting the fracture in quasi-brittle structures composed of steel alloys near V-notch tips presents a significant challenge. We investigate to which extent the continuum damage approach predicts the failure load F_c^Exp when applied to experiments performed on AISI 4340 alloy specimens tempered at two different temperatures and containing three different V-notch opening angles loaded to fracture under a four-point bending configuration. A series of experiments was performed for the characterization of the material parameters and fracture surface (including triaxiality) for the continuum damage model coupled with the J₂ theory of plasticity. Subsequently, this model was implemented within a finite element framework to compute the predicted failure load, termed F_c^FE. Sensitivity analyses were performed to identify the influence of notch radii and the representation of the supports on F_c^FE. A strong correlation was observed between F_c^FE and F_c^Exp for all configurations for both tempering temperatures, with predicted loads falling within the range of experimental observations for all V-notch angles. Additionally, a linear relationship was identified between the increase of F_c^FE and V-notch radii. These non-linear analyses have also revealed that for these high-strength steel specimens, it is crucial to model supports as linear elastic, as rigid supports led to underestimated F_c^FE. The presented methodology has shown to be superior in predicting failure loads in these quasi-brittle steel structures compared to other more simplified linear approaches.