Placement defects in thermoset-impregnated rovings deposited along curved paths

Abstract

Wet Fiber Placement (WFP) is a novel process for manufacturing complex shaped parts from continuous fiber-reinforced polymers without semi-finished products. Here, dry fiber bundles (rovings) are in-line impregnated with a thermoset resin, followed by almost tension-free deposition. The freshly impregnated and limp rovings allow for placement in radii. Due to the lack of compression in deposition, subsequent consolidation, for example, via vacuum bagging, is required. However, this consolidation cannot compensate for defects already present in the deposited lay-up as they will typically occur when depositing rovings along curved paths. In this study, we deposited two carbon fiber rovings in radii between 5 and 2000 mm by WFP. The occurring defects were visually evaluated. Three main defects were observed: Fiber waviness, up-folding and twists. The extent of the defects was evaluated using image analysis techniques. Results show, that up-folding and twists are dominant for radii <100 mm, while for greater radii fiber waviness is the main defect. Up-folding and twists almost completely disappear for radii >500 mm, but a slight waviness is still observed. However, the effect of fiber waviness on the longitudinal stiffness is estimated to be small for radii >500 mm and perhaps acceptable for some applications.