Underwater contact explosion response of thin-walled UHPC cylindrical shells: Experiments and simulations

The damage mechanisms of thin-walled UHPC shells subjected to underwater contact explosions remain insufficiently understood. This study conducted contact-explosion tests on air-backed UHPC cylindrical shells using 20, 30, and 40 g TNT charges and quantified damage on the blast-facing and rear surfaces through three-dimensional laser scanning. An arbitrary Lagrangian-Eulerian fluid-structure interaction model incorporating strain-rate effects was developed and validated against the experimental results. Parametric analyses were subsequently performed by varying the charge mass, shell thickness, and outer diameter, and the structural responses were normalized using the relative charge scale Π e and relative thickness Π h . The results show that the high dynamic compressive strength of UHPC suppresses localized crushing on the blast-facing surface, whereas tensile-wave reflection at the air-backed rear surface governs spalling. The first 3 ms after detonation contributed 99.19% of the cumulative pressure impulse over 0-30 ms, demonstrating that subsequent bubble evolution had a limited effect on the final damage. Increasing the charge mass promoted through-thickness damage coalescence, whereas increasing the shell thickness suppressed it; near the critical state, an 8.3% increase in charge mass triggered a transition from spalling to punching. Increasing the outer diameter weakened local restraint and enhanced global structural motion. Bending, spalling, and punching failure were distinguished in the Π e -Π h parameter space, providing a dimensionless basis for failure-mode prediction.