Research on Structural Failure of Ring-stiffened Carbon Fiber Composite Shells under Hydrostatic Pressure

To elucidate the influence of design parameters on the failure behavior of ring-stiffened composite pressure hulls, the finite element method to analyze the stability and strength failures of the annular ring-stiffened carbon fiber composite shell are analyzed. Parametric models for analysis of shell stability and strength are developed and validated against established benchmarks. Within the investigated parameter ranges, when the length-to-diameter (L/D) ratio ranges from 2 to 4, the peak material-strength failure load occurs at ply angles of ±0° and ±50°, and is independent of L/D. The critical buckling pressure decreases with the increasing of the L/D and increases with the number of stiffeners, peaking at ±50° ply angles. For L/D ratios greater than 4, material-strength failure loads within the ±45°-±75° ply-angle range exceed critical buckling pressure throughout, so buckling becomes the dominant failure mode and the buckling-pressure peak shifts to ±30° ply angles, while the influence of stiffeners weakens. At small thickness-to-radius (t/R) ratios (0.02), the critical buckling pressure is lower than the strength failure load over the full angle range, and the strength failure may occur only between ±20° and ±47° ply angles. As the t/R increases, the buckling pressure rises significantly, narrowing the gap between buckling and strength loads, with the potential strength failure confined to the ±20°-±40° ply-angle window. For the large t/R ratios (0.08-0.15), the growth rate of the critical buckling pressure far exceeds that of the strength failure load, so failure is dominated by strength destruction. With constant rib weight, the critical buckling pressure increases with rib height, but once the height-to-width ratio exceeds 4, the gain stops. Moreover, an excessively narrow rib width reduces structural stability.