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An approximate quasi-static theory is developed to predict large plastic deformation and perforation of spherical shells subjected to impact by blunt-ended projectiles at normal incidence. Based on experimental observations for quasi-static load-displacement characteristics, the problem of a spherical shell under normal impact by a flat-ended missile may be analyzed through the solutions to that of an equivalent circular plate struck transversely by the same missile. It is shown that the approximate theoretical predictions with a = 30 (here a is an empirical constant) are in good agreement with experimental data, in terms of maximum permanent transverse displacements and dimple radii. Furthermore, a theoretical formula for ballistic limits of spherical shells under missile impact is presented and the range of applicability of the theory is discussed.

An experimental investigation is reported on the dynamic response of a clamped circular plate struck transversely by a mass at any point along a radial line. A study is made of the variation of the failure mode with a change of striker diameter-plate thickness ratio, together with an assessment of transverse shear effects and the energy-absorbing capacity for impact velocities up to 12.2 m/s. The experimental results show that the steel and aluminium alloy targets fail by plugging with a plug having approximately the same diameter as the striker, which has a blunt end. The experimental results also show that the energy-absorbing capacity of a plate is reduced significantly when struck by a mass close to the supports compared to a strike at the centre and that the transverse shear force plays a more dominant role when a mass strikes close to the supports. A new criterion for the design of metal targets against projectile impact is proposed.