Strength of the Layered Cylindrical Shell of Composites Under Internal Pressure with Regard to External Damage

The strength of a layered shell structure of composite materials is investigated by combining modern strength criteria, the theory of deformable solid orthotropic medium mechanics, and methods of fracture mechanics. An adapted method of determining the limit state is used to assess the bearing ability of layered shell structures that have supercritical defects in the form of surface operational damages. The problem is solved analytically and numerically via the finite element method. A finite-element three-dimensional shell model of strength research is considered as a two-layer body, each layer of which is a composite material with given physical and mechanical characteristics, taking into account the structure of composite materials and the relations between the relevant components. To assess the strength of the developed model with a surface roundsegment damage, a crack is additionally introduced, which surface length and depth of propagation in the body of the upper layer of the cylindrical composite shell are varied. The obtained dependences of the parametric length and crack front on the limit values of the internal pressure are analyzed, fixing the moment of its displacement for this type of material and determining the limiting equilibrium state of the shell at the fracture stage. Evolution curves of crack resistance force characteristics in the form of stress intensity factors are constructed. The limit state analysis is based on the values of the critical stress intensity coefficients obtained due to mechanical tests of bidirectional fiber composite specimens with notches. The results obtained using the refined method of strength assessment are compared with the experimental ones, showing their close correlation.