Dynamics and Strength of Metal-Composite Cylinders on Internal Explosion Against the Thickness and Properties of Metallic and Composite Layers. Part 2. Numerical Simulation of Thick-Walled Cylinders and Effect of Stress Components on Strength*

The effect of the metallic layer thickness on the stress-strain state and strength of thick-walled metal-composite cylinders of total constant thickness under internal dynamic pressure produced by the explosion of a charge uniformly distributed along its axis in air at the constant total-to-running charge mass ratio $\xi$ = 1.421 mm was numerically investigated. The strength of the cylinders was evaluated by the generalized Mises criterion. It is numerically and analytically proved that the strength of circularly reinforced cylinders from the composites of low tensile strength in the isotropy plane is primarily governed by the wave processes across the shell width and, as a consequence, by radial and axial tensile stresses, viz the larger they are, the lower the strength. Circumferential tensile stresses, on the contrary, improve the strength in most cases, i.e., only strengthen the structural element and increase the safety margin. Cylinders with four outer layer composites are examined. They are double-layered: the inner layer is steel (St20), the outer layer is a circularly reinforced composite. At given $\xi$ and the total constant cylinder thickness $H$, the optimum in strength terms ratio ${\beta }_{opt}$ of the metallic layer thickness $h$ to $H$ is strongly dependent on a composite (i.e., its physicomechanical characteristics) and varies within 0.3–0.7. The plastic deformation of the inner steel layer has a significant impact on the shell strength, the account of the plastic steel deformation substantially changes the dynamics of objects both qualitatively and quantitatively, thus, the strength function can be reduced by more than 50% compared to the elastic calculation. The strength of metal-composite cylinders is proved to be very sensitive to the wave phenomena along the radial coordinate. Sometimes at a certain ratio of layers $\beta$ (about 0.7), the charge mass ratio $\xi$ (and hence the absolute charge mass $M$) can be increased more than twice without deterioration of the strength requirements, while the $\beta$ deviation by only 1.5% from that at given $\xi$ would lead to the cylinder fracture.