### 5.2.1. Introduction

In the analysis of layered composite structures, shell elements are widely used to keep the computational effort reasonable. In-plane stresses and even transverse shear stresses can be predicted with accuracy using shells based on the first-order shear deformation theory (FSDT). However, in the analysis of thick-walled curved structures, interlaminar normal stresses (INS) can play a significant role. The normal stresses may affect the failure mode or even cause delamination failure. INS computation is not commonly available in shell element formulations, which leads to use of computationally expensive solid modeling instead.

The approach by Roos et al. ([ 14 ]) for INS computation of doubly curved laminate structures represents an alternative for solid modeling. The basis for the INS calculation is the displacement solution obtained from a shell based model. In conjunction with the INS approach, transverse shear stresses are computed with the approach presented by Rohwer ([ 11 ]) and Rolfes ([ 12 ]). When considered at layer interfaces, transverse shear stresses are referred to as interlaminar shear stresses (ISS).

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