First-ply failure load prediction of delaminated pre-twisted rotating composite conical shells

A finite element-based method for determining the first-ply failure (FPF) strengths of delaminated composite pre-twisted shallow rotating conical shells subjected to a central point load is presented in this work. The influence of transverse shear deformation and rotary inertia are accounted for in the eight-noded shell element employed in the present analysis based on Mindlin's theory. The delamination of the crack front is modeled using the multi-point constraint algorithm, while the initial stresses arising out of rotation are determined iteratively. The present study uses the maximum strain, maximum stress, Hoffman, Tsai-Hill, and Tsai-Wu failure criteria to arrive at the FPF loads. The results illustrate the effect of some vital parameters like stacking sequence, pre-twist angle, aspect ratio, presence and location of delamination, and rotational speed on the FPF in the delaminated composite conical shell with an initial twist. The spatial distributions of the stresses in the material directions and deflections identify the first-ply failure zones at the failure loads obtained. It is found that the FPF strengths increase on increasing the aspect ratio and non-dimensional rotational speed whereas the strength decreases with size and number of delaminations. The stresses developed at the FPF loads are lower in non-rotating conical shells compared to rotating shells.