Application of hydrogen influenced cohesive laws in the prediction of hydrogen induced stress cracking in 25 percent Cr duplex stainless steel

摘要

Cohesive zone finite element modeling is applied in the simulation of hydrogen induced stress cracking in 25 percent Cr duplex stainless steel. Hydrogen influence is implemented in linear and polynomial cohesive laws. Suitability of the laws in prediction of hydrogen induced stress cracking is investigated by applying models of U and V-notched tensile specimens representing a 25 percent Cr duplex stainless steel component submerged in sea water under cathodic protection (CP). Fracture prediction is performed by a three step procedure; elastic plastic stress analysis, stress assisted hydrogen diffusion and cohesive stress analysis. Local cohesive stress fields as well as the time to fracture initiation are investigated as a function of the shape of the traction separation laws and the element size for three levels of tensile stress. Simulated results are also compared with results from laboratory tensile tests and discussed with respect to the suitability of describing fracture initiation and fracture mechanism of the steel. The results show that the polynomial law and a mesh size of 0.5 mu m gives the most accurate description of the local cohesive stress field. The simulated time to fracture is closest to laboratory test results for stresses of 0.85-0.9 times the yield strength.