Optimal autofrettage process design for enhancing the fatigue life of the ultra-high-pressure hydrogen valve

This study investigated the optimal autofrettage pressure and design method for improving the fatigue life of an ultra-high-pressure hydrogen valve attached to an ultra-high-pressure hydrogen storage vessel, which is responsible for the supply and control of hydrogen gas. The theoretical values calculated by the theoretical equation for determining the hoop residual stress formed by autofrettage pressure in a circular cylinder and the analytical values of the hoop residual stress obtained through finite element analysis of the autofrettage process in a porous circular cylinder using the commercial finite element analysis program ANSYS Workbench were well matched. Based on the analysis technique obtained for the porous circular cylinder, a quantitative target lifespan was examined for the ultra-high-pressure hydrogen valve with the shape of a porous circular cylinder, considering the maximum pulse pressure. As a result, the previously manufactured ultra-high-pressure hydrogen valve did not meet the quantitative target lifespan. To address this, the optimal values of displacement at specific locations where fatigue failure occurs and autofrettage pressure were designed using response surface methodology (RSM). Through this, fatigue life of 172710 cycles more than 150000 cycles (quantitative target lifespan) was obtained.