Approach to net-shape preforming using textile technologies. Part II: holes

Over the last decade studies have been performed on the on-line manufacturi ng of bores and the integration of bolts or other mechanical fasteners into the reinforcing fibre structure. Textile technologies provide the possibil ity for on-line integration of bolts or other fasteners into the dry prefor m. Accuracy, efficiency and properties of the built notched textile structu re are different for each method investigated. However, using these technol ogies drilling or any other mechanical post treatment can be prevented. Thu s, mechanical properties are different due to non-cut fibres or changed fib re orientations. Mechanical post-treatment free manufacturing offers econom ical advantages if a simple preforming process can be applied. Braiding, SD -weaving, warp- and weft-knitting, biaxial reinforced weft-knitting and Tai lored Fibre Placement (TFP) technologies were evaluated relative to their p otential for the integration of bolts. This study focuses on the comparison of on-line manufactured bores to those drilled mechanically. Although ther e are many factors which influence joint strength, such as joint geometry, fibre orientation, stacking sequence and through-the-thickness pressure [Ca manho PP, Matthews FL. Proceedings of ECCM-8, vol. 2, Naples, Italy 1998. p . 47-53], no study reports on direct manufacturing of holes. Tn this study, the variability and influence of on-line manufacturing is investigated wit h respect to diverse textile parameters. Open-hole tension and bearing-stre ngth testing methods were applied to characterise mechanical behaviour, whi le stereo-microscopy was used to evaluate achieved qualities of the Fibre R einforced Plastic (FRP). Near net-shape holes improved the mechanical perfo rmance of the drilled holes slightly for particular load cases and textile technologies. The correct integration of the spacing bolt into the textile process was found to be essential for an accurate positioning of the joints and thus the placement of the preform into the mould. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.