Free Edge Stresses In Composite Laminates Research Articles

Finite-Layer Method: a Unified Approach to a Numerical Analysis of Interlaminar Stresses, Large Deflections, and Delamination Stability of Composites Part 1. Linear Behavior

A new method for a stress–strain analysis of layered composites, named the finite-layer method, is proposed, which is based on the consideration of each particular layer as a constituent of the entire laminate. This method serves as a unified approach to the development of new algorithms for computing stresses in composite layers, interlaminar contact stresses, large deflections, and critical buckling loads of thin-walled laminated structures with delaminations. The calculation of a laminated structure is reduced to solving a boundary-value problem for a system of first-order ordinary differential equations. The number of equations depends on the number of layers in the composite. The resolving system of differential equations is a stiff system. The stable numerical method of discrete orthogonalization is used for solving the boundary value problem. Part 1 is dedicated to the application of the proposed method to a linear analysis of free-edge stresses in composite laminates, to a study of the deformation of composite plates with delaminations and bending of composite beams with patches, and to calculations of adhesive joints.

Finite element analysis of free-edge stresses in composite laminates under mechanical an thermal loading

In this paper, a multi-particle finite element [Nguyen VT, Caron JF. A new finite element for free edge effect analysis in laminated composites. Comput Struct, accepted for publication] is applied for general laminated and is shown to be capable of simultaneously predicting global and local responses. The analysis of free-edge stresses of composite laminates subjected to mechanical and thermal loads is performed using this C o eight-node layer-wise finite element after a classical bending validation. Laminates with finite dimensions are considered and three-dimensional out-of-plane stresses in the interior and near the free edges are evaluated. The results obtained with this finite element modelling are compared with those available in the literature. The present calculation provides accurate stresses and can be utilised as and operational tool to predict interlaminar stresses under the loads of mechanical and thermal combined.

Multi-layer higher-order finite elements for the analysis of free-edge stresses in composite laminates

The analysis of the free-edge stress distributions in composite laminates under uniaxial tension is approached by a finite element technique based on a multi-layer higher-order laminate theory. Several finite elements corresponding to different through-thickness assumed distributions of the displacement unknowns are developed. Numerous stacking sequences are examined in the applications. The results are compared with the ones obtained by various investigators with other modelling approaches. The use of the proposed technique is demonstrated to be simple and effective both for the analysis of in-plane and out-of-plane distributions of intralaminar and, noticeably, interlaminar stress components. © 1998 John Wiley & Sons, Ltd.

An efficient stress function approximation for the free-edge stresses in laminates

A solution method is derived for determining the free-edge stresses in composite laminates. The method is based on expanding stress functions in terms of a harmonic series in the thickness direction. Using the principle of minimum complementary energy, a system of ordinary differential equations is derived for the distribution in the width direction. Cross-ply and angle-ply laminates are examined to establish the validity of the solution. Eight- and 16-ply quasi-isotropic laminates are also examined to demonstrate a convergence criterion based on average stress. The method proves to be a relatively simple and efficient approach for this problem.

Simple Solutions of the Free-Edge Stresses in Composite Laminates under Thermal and Mechanical Loads

Intense and localized interlaminar stresses generally occur in a narrow boundary region near the free edge of a multilayered anisotropic laminate under mechanical and temperature loads. Quantitative measures of interlaminar action across interfaces may be readily obtained through purely algebraic operations, even if nonlinear and inelastic material behavior becomes significant in the boundary region due to severe strain concentration. These measures are the limiting values of the Lekhnitskii stress functions F and $$ (and of the normal derivative of F) along interfaces and toward the interior region of the laminate. In the present work, they are used as the basis of an exceedingly simple and efficient method of interlaminar stress analysis that is potentially applicable to free-edge problems involving nonlinear thermoelastic constitutive relations. Example solutions are obtained for symmetric, four-layer, cross-ply and angle-ply laminates under a temperature load and two different types of strain loads, and the results are found to be in reasonable agreement with the existing numerical and analytical solutions based on elaborate analysis methods.