Composite materials are increasingly often used in high loaded thick-walled curved shells. The stress state involves interlaminar normal and shear stresses, which can cause structural failure by delamination due to the low interlaminar strength. The paper presents a new method for singly and arbitrary doubly curved thick-walled laminate strength analysis including interlaminar shear and normal stresses using common layered 3-, 4-, 6-, or 8-node shell elements. Commercially available FEM packages do as of yet not offer interlaminar normal stresses as a result of layered shell element analysis. On the other hand, a fully three-dimensional FE calculation using solid elements is often not possible due to computing power or/and complex geometry. A numerically efficient post process method is used to complete the three-dimensional stress tensor. A differential equation of second order for the through-the-thickness displacement w(r) is derived from the radial equilibrium equation in cylindrical coordinates. The input values are the in-plane strains, stacking sequence of the laminate, material properties, and geometry information such as the curvature radii. All these parameters are available from a finite shell element model. The solution of w(r) is found by using the finite-differential method. The interlaminar normal stresses are obtained by combining the through-the-thickness displacement solution w(r) with the stress-strain equation. This method is linked with commercial shell elements. Three-dimensional failure criteria applicable to unidirectional fiber composites, namely Tsai-Wu, Hashin, Maximum Stress and Puck, are implemented to predict failure or factors of safety. Strength and stress analyses are presented for different geometries, materials, and laminates and are compared with finite solid modeling results and experimental evaluation.
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