Peculiarities of Strengthening of Spherical Composite Pressure Vessels with Thin Metal Shells Under Static and Dynamic Loads. Part 2. Dynamic Loading

An elastic boundary-value problem was solved for a two-layer sphere acted upon by an internal dynamic pressure generated by an explosion of a spherical explosive charge. The peculiarities of solutions for shells with an ultrathin inner metallic layer were studied. An analysis was performed to compare the static case with the dynamic one. The peculiarities of such solutions were pointed out. Taking into account the data earlier obtained by the authors, it was proved analytically and numerically that in two-layer spherical metal composite vessels, the hoop stresses in the inner layer (S₁) could be much higher than the stresses in the outer layer (S₂) if the thickness of the inner metallic layer was much smaller than that of the outer layer. An exact asymptotic ratio S₁/S₂ for static and dynamic problems was obtained. It is shown that in such structural elements at small relative thicknesses of the metallic layer, there can be a softening region. A formula was derived, which made it possible to predict in an engineering approximation the presence or absence of a softening region. For the dynamic problem, it was found that with decreasing thickness of the inner more rigid layer, the hoop stresses in it grew in proportion to the ratio of the spherical rigidities of the materials of the inner and outer layers. This can lead, as in the static case, to the fact that the pseudo-reinforcement of the composite shell with a too thin inner fairly rigid and strong metallic layer will not only be inefficient, but also can cause a failure of the inner layer and hence of the shell as a whole under loads that are fairly safe for the composite shell without the inner pseudo-reinforcing layer.