Through-thickness stress in curved laminates of single- and double-skinned construction

This paper is concerned with the calculation of through-thickness stresses in components in the form of curved shells and then describes the determination of the through-thickness strengths of some fibre-reinforced tubes. The through-thickness stresses in thin shells are often assumed to be zero and this is normally justified by the fact that they are much lower than the in-plane stresses. However, if the shell is of laminated construction, the through-thickness strength can also be relatively low compared with the in-plane strength, so even small levels of tensile stress in the through-thickness direction can lead to damage by delamination. This paper first presents an equilibrium method of calculating the normal and shear components of these stresses for singly curved shells and rings of single- or double-skin construction. The formulae derived are then used to analyse a delamination test in the form of a split ring which is then used to determine the delamination strength of a number of filament wound tubes with various matrix compositions and lay-up geometries. As the changes in curvature can be large, the entire formulation is presented in terms of the current (deformed) coordinate system and the Cauchy stress.