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

Abstract

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 FcExp 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 FcFE. Sensitivity analyses were performed to identify the influence of notch radii and the representation of the supports on FcFE.A strong correlation was observed between FcFE and FcExp 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 FcFE 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 FcFE.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.