Effect of autofrettage technique upon fracture strength of metallic liners for composite overwrapped pressure vessels

The finite element model of composite overwrapped pressure vessel (COPV) including a circular surface crack in the liner was constructed with the sub-model technique. Based on the stress analysis of the metallic liner before and after autofrettage technology, the J -integrals along the crack front under operating pressure were calculated by the domain integral method. The objective was to investigate the crack tip strength under the following two cases: whether considerd the autofrettage or not and autofrettage with different pressures. Results show that the J -integrals increase significantly after autofrettage and improve slightly due to a superior autofrettage pressure; the deeper crack would lead the J -integrals to become larger and the curve to become sharper. It could be concluded that the larger the autofrettage pressure or crack size, the more likely the crack will open. Therefore it is necessary to analyze the fracture behavior of metallic liner when determining the autofrettage pressure.