tailieunhanh - 3D Fibre Reinforced Polymer Composites Part 10

Tham khảo tài liệu '3d fibre reinforced polymer composites part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3D Fibre Reinforced Polymer Composites c Figure Illustrations showing the configuration of the a modified lock stitch b lock stitch and c chain stitch From Morales 1990 . Figure Illustrations showing a straight b diagonal c zig-zag and d cross stitching Reproduced from Dransfield et al. 1994 . Stitched Composites 167 The damage to preforms caused by stitching is one of the major drawbacks of this technique. Stitching can cause many different types of damage and these are shown in Figure . The different damage types are Fibre breakage-. Breakage occurs from abrasion generated by the needle and stitch yarn sliding against the fibres during the stitching process. Breakage in prepreg tape can also occur by the needle tip crushing the fibres which cannot be easily pushed aside by the needle because of the resin matrix. Fibre breakage in a dry fabric preform in shown in Figure . Fibre misalignment Significant misalignment of the in-plane fibres occurs because they are distorted around the needle and stitch thread. The amount of distortion to fibres depends on the fibre density stitch yarn thickness and in some cases stitching density and maximum misalignment angles of between 5 and 20 have been measured Mouritz and Cox 2000 Mouritz et al. 1996 Reeder 1995 . A schematic diagram and photograph of fibre misalignment is shown in Figures and . Fibre crimping Crimping occurs by the stitches drawing the fibres at the surface into the preform. The effect of fibre crimping is illustrated in Figure and the severity of crimping increases with the line-tension on the stitching yarn. Resin-rich regions The crimping and misalignment of fibres in preforms leads to the formation of small regions with a low fibre content around the stitches Figure . This leads to the formation of resin-rich regions when the preform is consolidated into a composite using liquid moulding processes. Stitch distortions The stitches can be distorted by heavy compaction of the