The influence of splits on the constraint and stress triaxiality fields on SE(B) and SE(T) specimens

Abstract

This study examines the influence of splits, defined as brittle delaminations perpendicular to the main crack plane, on constraint conditions and stress triaxiality fields in fracture mechanics specimens under high (SE(B)) and low (SE(T)) constraint configurations. Numerical models with stationary and ductile growing cracks were employed to analyze split behavior in DH36 steel. For crack growth, the Modified Mohr-Coulomb (MMC) fracture criterion was applied for initiation, combined with post-initiation softening. Stress triaxiality was assessed using η (or h) and parameters. Complementary experiments were performed at room temperature and –60 °C with SE(B) specimens of DH36 and X70 steels, and fractographic analysis provided indirect validation of numerical predictions.Results show that splits markedly reduce constraint level in conditions deemed as high-constraint, while their effect is seemingly negligible in low-constraint configurations. This is exacerbated by the linear extension and orientation of the split in the fracture surface. Numerical analysis proves that splits affect not only local stress triaxiality near the crack tip but also the constraint level across the ligament. Larger splits reduce constraint over wider regions, though the effect diminishes once the crack tip reaches the split tip. High-stress triaxiality zones around split tips explain the brittle growth of delamination observed experimentally.This work provides further understanding of the influence of split on constraint and stress fields, contrasting low- and high-constraint scenarios, and the novel use of crack growth models that allows the assessment of splits in the behavior of the fracture process.