A design strategy to reduce edge delamination in polymer composites

We are developing and exploring the concept of in-plane tiling of composite laminates, called MOSAIC, to mitigate or even control delamination at free edges due to interlaminar stresses. Initial mechanical testing has shown that MOSAIC composites with uniaxially carbon-fiber reinforced tiles retain the stiffness levels of traditional uniaxially reinforced composites but display only half as much strength. The reduction in strength is attributed to the formation of resin-rich pockets between adjacent tiles. We have performed detailed finite element analyses to identify the critical design parameters that affect the mechanical performance of uniaxially reinforced MOSAIC composites. The effects of resin-rich pocket aspect ratio (idealized as rectangular), oblique and free surface resin pocket placement, relative elastic and strength properties of resin and tile, and tile overlapping schemes (pocket stacking geometry) have been investigated. Based on the results, a novel interleaved scarf composite joint with outer continuous layers is proposed and found to have superior performance. We have also developed tiling schemes that will allow blending of disparate laminates (lay-ups), where a lay-up suitable for suppressing interlaminar stresses could be substituted at necessary locations in place of another lay-up that may be more suitable for the global structural loads. Failure analyses of the finite element results using three-dimensional Hashin-Rotem failure criteria have shown the concept to be effective in the suppression of free-edge delamination in traditional quasi-isotropic and angle-ply laminates under tensile loading. While still at the early stage of investigation, MOSAIC shows promise as a new method for improving the durability of composite laminates in a wide class of applications.