FEM Analysis of Ductile Crack Growth in Fracture Transition Region for Steels with Different Void Nucleation Frequency.

Abstract

Local stress and strain fields in front of a crack have been computed by FEM analysis using a Gurson model which takes into account void nucleation and growth within the material. The original Gurson model has been revised to fit the actual material by introducing experimentally obtained deformation and fractographic data of the material. Calculation has been applied for the ductile-to-brittle transition regions up to the ductile crack growth stage in two steels with different transition behaviors. Higher magnitudes of local stress and strain as well as larger extensions have been shown for a steel which has less nucleated void volume fraction, resulting in higher resistance against the ductile crack growth. Local stress increases with lowering test temperature whereas local strain decreases. Insignificant temperature dependence of R-curves has been understood from the calculated J-integral values because of the cancellation of the stress increase and strain decrease. The calculated R-curves have been shown to be consistent with the experimentally observed ones.