EXPERIMENTAL INVESTIGATION ON THE PERFORMANCE OF CARBON-EPOXY LAMINATES CONTAINING GAPS AND OVERLAPS FABRICATED BY AUTOMATED FIBER PLACEMENT

摘要

Manufacturers use Automated Fiber Placement (AFP) as a fabrication process for large and complex composite parts. AFP shows great potential to transition from hand layup to an automated technique. An AFP machine consists of a computer-controlled robotic arm with a head at the end capable of constant placement of uncured preimpregnated carbon fibers grouped together to form bands called tows. AFP machines control orientation of fibers placed onto a mold to build the layup, but this method also creates defects which undermine the structural performance of the part. Primary defects observed by the aerospace industry are gaps and overlaps. Corresponding detection methods are labor intensive and time consuming. Proposed in this paper is an investigation on the effect of size and distribution of half gap/half overlap on mechanical performance of composite structures made with AFP techniques. The goal of this research is to better assess the strain-stress response subjected to both tensile and compression loading of such composite structures. By varying the orientation, size and number of defects embedded in carbonepoxy laminates, the effects of defects on tensile and compression performance have been experimentally examined to finally draw design guidelines. A Finite Element model has been developed to predict the mechanical behavior of laminates with embedded defects. Without out of waviness geometrical consideration, this FE model is overpredicting strength in case of defects oriented in the direction of the load, and underpredicting strength in case of defects in transverse direction of the load which shows the importance of out of plane waviness.