Stresses near a change of thickness in a continuous-fiber-composite plate

Citation

Kubr, Thomas J. (1991) Stresses near a change of thickness in a continuous-fiber-composite plate. Engineer's thesis, California Institute of Technology. doi:10.7907/rra5-sv66. https://resolver.caltech.edu/CaltechETD:etd-05072007-105324

Abstract

This thesis presents the results of a numerical investigation of the stresses near an abrupt change in thickness of a composite plate. The plate is a laminate of unidirectional, continuous fiber plies. The study is aimed at gaining insight into the failure behavior of co-cured stringer reinforced composite plates and shells.

The analysis is performed in a plane normal to the stringer axis. The problem formulation is similar to plane strain. Because orthotropic materials are involved, a solution method allowing three-dimensional displacements as functions of two spatial variables is applied. The method is called plane-coupled strain. Failure is assumed to initiate at the sharp 90° reentrant corner of the step-down geometry due to a rise in stresses. The resulting stress singularity is characterized for different combinations of stacking orders in the stepped plate. Stresses in the structure are determined by means of the finite element method.

The results are presented in two parts: The first describes the differences obtained with plane-coupled strain and classical plane strain; the second characterizing the stress singularity. The more computer intensive plane-coupled strain solution produces significantly different results for the stresses near the singularity. The character of the stress singularity is found to be highly dependent on the fiber direction of the material at the sharp corner.

The results for the stress singularity are used in an example failure criterion. Stacking sequences are examined with respect to their susceptibility to failure under different combinations of in-plane loading.

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