Failure Analysis of Layered Composite Structures: Computation and Experimental Investigation

Abstract

A geometric nonlinear finite element method based on the von Karman - High Order Shear Deformation Theory (HOST) is used to study the first-ply failure and the postbuckling behavior of laminated type composite structures. For this purpose and for the investigation of the failure responses improved 4-node layered shell finite elements are used. The finite element formulation is based on the third order shear deformation theory with four-node shell finite elements having eight degrees of freedom per node. The first-ply failure of laminates and the onset of delaminating process in first-ply failure computation are some of the features of geometric nonlinear formulation. The load-displacement curves for different types of graphite/epoxy laminates are obtained. Stresses are computed in order to determine the first-ply failure of the mentioned axially compressed laminated composite structure based on the maximal strain failure criterion. In this procedure postbuckling and failure behavior of axially compressed flat and curved composite panels are investigated numerically and experimentally. Computational results using linear and geometrically nonlinear analyzes are compared with experiments. The effects of stacking sequences on initial failure load are investigated. The HOST used here assumed the parabolic distribution of the transverse shear stresses across the laminate thickness. The displacement field for the parabolic transverse shear deformation through the shell thickness is $$ \begin{gathered} u_1 (x,y,z) = u + z\left[ { - a\frac{{\partial w}} {{\partial x}} + b\psi _1 - c\frac{4} {3}\left( {\frac{z} {h}} \right)^2 \left( {\psi _1 + \frac{{\partial w}} {{\partial x}}} \right)} \right] \hfill \\ u_2 (x,y,z) = v + z\left[ { - a\frac{{\partial w}} {{\partial y}} + b\psi _2 - c\frac{4} {3}\left( {\frac{z} {h}} \right)^2 \left( {\psi _2 + \frac{{\partial w}} {{\partial x}}} \right)} \right]u_3 (x,y,z) = w \hfill \\ \end{gathered} $$ (1)