Suppression of Edge Delamination Through Meso-Scale Structuring

We are developing a new class of fiber-reinforced polymer composite materials to facilitate imbedding multifunctional features and devices in material systems, and to manage interlaminar stresses at free edges and cut-outs. The idea is centered on introducing one more level of design space by composing plies with individual tiles possessing the same degrees of design freedom that are associated with individual plies. In this work, we have focused on tiling schemes that will allow blending of laminates (lay-ups), where a lay-up suitable for suppressing interlaminar stresses could be placed at necessary locations whereas another lay-up could be used for the main objective. This results in the introduction of matrix-rich tile-to-tile interface pockets in the blending region. Preliminary mechanical testing shows that uniaxially reinforced tiled composites attain stiffness levels near those of their traditional counterparts, yet with a potential degradation of strength. We used the finite element method to investigate the effects of resin-rich pocket size, the use of supporting continuous layers, tile size, and tile overlapping (interface stacking) schemes on stress distribution around interfaces in uniaxially reinforced tiled composites, with the aim to identify parameters controlling overall strength. We discovered that alignment of the resin-rich pockets through the thickness exacerbates stress-concentration and that outer continuous layers on the composite may help in better load transfer. As a first step in the application of this technique for the suppression of delamination at the free edges of holes in laminates, a bilaminate material was modeled, and the concept was shown to be effective in the suppression of edge delamination.