Influence of embedded gap and overlap fiber placement defects on the microstructure and shear and compression properties of carbon-epoxy laminates

This paper presents results from an experimental study of the influence of embedded defects created during automated fiber tape placement, on the mechanical properties of carbon/epoxy composites. Two stacking sequences have been examined, [(-45 degrees/+45 degrees)(3)/-45 degrees] and [90 degrees(4)/0 degrees(3)/90 degrees(4)], in which gaps and overlaps have been introduced during fiber placement. These materials have been cured in an autoclave either with or without a caul plate, then analyzed by ultrasonic C-scan. The microstructures were characterized by scanning electron microscopy. In-plane shear tests were performed on the +/- 45 degrees laminates and showed that the use of a caul plate does not affect mechanical behavior of plies in the embedded defect region. Compression tests were performed on 0 degrees/90 degrees laminates and in this case the presence of a caul plate is critical during polymerization as it prevents thickness variations and allows defects to heal. (C) 2015 Elsevier Ltd. All rights reserved.