Experimental and numerical investigation on the open-hole compressive strength of AFP composites containing gaps and overlaps

Laminated composite structures manufactured via the automated fiber placement process inherently contain process defects know as gaps and overlaps. These defects raise concerns when they are located on or near holes intended for mechanical fastening. This investigation attempts to predict the effect of automated fiber placement-generated defects on the open-hole compression strength by combining both experimental tests and numerical simulation. Tested open-hole compression specimens containing gaps and overlaps oriented at 0° or 90° and centered on or shifted near the hole show that, depending on their location, the gaps and overlaps may have negative, negligible, or positive effects on the open-hole compression strength. The better than expected effects are compatible with microscopic observations that clearly show the rearrangement of the plies during the consolidation process, which prevent the formation of deleterious discontinuities. Incorporating these observations in a numerical model, which simulates gaps and overlaps embedded inside the composite laminates, and applying a progressive failure analysis, confirms that the effects of automated fiber placement defects depend as much on their type as on their location relative to the hole center. Finally, the results obtained from a parametric study provided further explanation on the effects of automated fiber placement defects on the failure strength of perforated composite laminates.