Study on Autofrettage Process Parameters Selection and Methods Improvement of Hoop Wrapped Composite Vessel

Abstract Current selection criteria for autofrettage pressure in hoop wrapped composite vessels are inadequately defined, critically lacking consideration of axial structural safety and fatigue life requirements. To address this, the axial structure safety of the vessel during the autofrettage process within the respective selection range chosen by different criteria was analyzed. Results clarified the axial burst risks within conventional selection ranges. A safety criterion constraining pressure between the hydrostatic test and the liner axial burst limits was established. Fatigue analysis using fracture mechanics revealed that the mechanism of the autofrettage process enhances fatigue life of vessels by reducing crack-tip stress intensity factors due to residual stresses. The results also indicate that under axial structural safety constraints, the maximum fatigue life of vessels after autofrettage is only 12,100 cycles, which is significantly lower than the design requirement of 37,540 cycles. This demonstrates that current autofrettage processes fail to ensure processing safety and adequate fatigue life. To resolve this, an improved method imposing axial constraint to reduce stress and enhance liner axial capacity was proposed, and its feasibility was validated through numerical simulations. By enhancing axial load-bearing capacity, this approach expands the autofrettage pressure range, introducing higher residual stress that extends fatigue life to meet design requirements.