Layer waviness effects on compression strength of composite laminates: progressive failure analysis and experimental validation

Out-of-plane layer waviness, a manufacturing-induced imperfection in multidirectional composite laminates, can produce significant decreases in compression strength. To date, failure predictions based on initial "first-ply" failure analyses as well as compression strength reductions based on the ply fraction containing waviness have shown limited agreement for compression-loaded cross-ply laminates with idealized formations of layer waviness. The objective of this investigation was to extend previous research by employing progressive failure analysis to predict the ultimate compression strength of carbon/epoxy composite laminates with layer waviness. A finite element modeling methodology was developed using cohesive elements available in the commercial finite element code ANSYS to model the formation and growth of delaminations at layer interfaces. Progressive failure analysis within individual composite layers was performed using the Hashin failure criterion and subsequent reduction of appropriate stiffness properties of the failed elements. Strength predictions were compared to mechanical test results obtained for a variety of layer wave formations intentionally fabricated into otherwise wave-free cross-ply laminates. Results suggest that the computational approach used for progressive failure analysis is well suited for predicting strength reductions due to realistic formations of layer waviness in composite laminates.