Optimized fiber prestress for reduction of free edge stresses in composite laminates

An analytical procedure is described for evaluation of the effect of release of fiber prestress, applied prior to matrix consolidation, on stress distribution in individual plies and at free edges of laminated composite plates. Both thermal changes, piecewise uniform transformation strains in the plies and overall mechanical loads can be considered in the analysis. The thermal and transformation load contributions are decomposed into superpositions of certain uniform fields with mechanical loads. Release of fiber prestress is regarded as an equivalent uniaxial compression applied at the edges of each prestressed ply. Optimized distributions of fiber prestress are found in individual plies such that stresses in both laminate interior and at the free edges remain within allowable limits, while the applied mechanical load may change from zero to a certain maximum value. Specific results are found for cross-ply and quasi-isotropic symmetric S-glass/epoxy laminates under tension. They clearly demonstrate the substantial potential of fiber prestress in damage control and prevention in laminated composite structures.