Modeling dynamic fracture of hydrogen pipe burst incorporating HELP and hydrogen solid solution strengthening mechanism

Abstract

A constitutive model that simultaneously incorporates hydrogen enhanced localized plasticity (HELP) and hydrogen solid solution strengthening was developed. By writing the VUMAT subroutine, it was developed to predict dynamic fracture of hydrogen pipe burst. Burst experiments were conducted on hydrogen-charged pipes with hydrogen concentrations ranging from 0 to 8.70 ppm, and the numerical model was verified in terms of crack propagation behaviors and fracture patterns. Internal gas decompression, crack propagation behavior, crack length and speed were obtained and analyzed in detail. The results showed that the cracks on both sides of the uncharged pipe propagated axially for a certain distance and then stopped. In contrast, the hydrogen-charged pipe exhibited similar initial axial cracks propagation but subsequently both branched, and the branching cracks propagated along the pipe in the circumferential direction. The fracture behavior of the hydrogen-charged pipe was more severe, with pronounced plastic deformation observed in the middle section. Compared to the case of 0 ppm, the axial crack length of hydrogen-charged pipe was reduced by 50-60 mm at 3.46 ppm and by 80-100 mm at 8.70 ppm. Moreover, hydrogen ingress accelerated the crack propagation speed, the maximum crack propagation speed increased by approximately 7 m/s for each 1 ppm increase in hydrogen concentration. It was further revealed that under the damage constitutive model considering the HELP mechanism, the incorporation of hydrogen solid solution strengthening reduced plastic deformation and slowed damage accumulation, thereby delaying crack branching. Compared with the existing models, the constructed model is more accurate in dynamic damage and fracture prediction analysis. It is more consistent with the experiment results.