Fabric reinforcements John Summerscales University of Plymouth Outline

Fabric reinforcements John Summerscales University of Plymouth

Outline of this lecture • • • woven fabrics braids knitted fabrics stitched fabrics (non-crimp fabrics) bonded/felted fabrics

Fabric description • warp fibres picks (shots) run full length of the fabric • weft fibres (shuttle direction in weaves) ends run across the fabric Weft in weave Course in knit Warp in weave Wale in knit • fabrics are designated by areal weight normally grams/square metre (gsm)

Balanced fabric a balanced fabric would have • equal numbers of equal weight tows/metre in both warp and weft Crimp crimp ratio = yarn length/cloth length

Woven fabrics 1: weave styles • plain • high crimp, poor mechanical properties • twill • intermediate properties • satin low crimp, good mechanical properties • but beware of orientation of each face • • also matt, leno, flow-enhancement …

Woven fabrics 2 • plain weave • 2 orthogonal sets of fibres (ηo = 1/2) • high crimp, hence out of plane orientation ( ηo < 1/2)

Woven fabrics 3: twill weave • note the recurring diagonal pattern

Woven fabrics 4: satin weave • different fibre orientation on each face • interlace position is irregular

Woven fabrics 5: Flow-enhanced • constrained tow (blue) creates flow space • mechanical properties decrease

Triaxial fabrics • Triaxial (three directions in a single layer) • usually -60°/0°/+60° • Image from http: //hexdome. com/weaving/triaxial/weaving/index. php

Three-dimensional fabrics • 3 -D weaving • usually multi-layer • • • 3 D angle interlock (shown) 3 D orthogonal (90° binder) used for preforms Image from http: //www. designscopecompany. com/en/infopattern/products. php? itemid=75&lang=en&page=product. Tree Layer to layer interlock weave Angle interlock weave Orthogonal non-crimp interlock weave Images from AE Bogdanovich and MH Mohamed (3 Tex Inc), SAMPE Journal, 2009, 45(6), 8 -28.

Braid • interlacing three or more threads to produce a tubular reinforcement with fibres at ± 45° to the principal axis of the tube • braid calculator (A&P Technology) • image from • eurocarbon. com/overbraiding. htm (NLA) • Videos: Braiding the A-pillar for the Lexus LFA sports car • Overbraiding at Eurocarbon (72 second 7 MB MPEG) •

Knitted fabrics • knitting is intermeshing of loops of yarn • Marvin (1961 -69) knitted rocket nose cones • can form complex shapes or create a matrix for aligned fibres: • WIWK = weft-insertion warp knit or = warp-insertion weft knit • image from http: //en. wikipedia. org/wiki/Knitting

Stitched (non-crimp) fabrics detail of the stitch photo of real fabric cross-section of laminate • unidirectional layers stitched together • Beware! stitch fibre may be incompatible with the matrix • images from http: //www. aer. bris. ac. uk/research/structures/mrw/sylvain. html

Bonded/felted fabrics • chopped strand mat • Unifilo continuous random swirl fibre mat • bonding reinforcing scrims (e. g. Crenette)

Pre-impregnated fabrics “prepreg” • pre-impregnated fibres/fabrics (lecture C 8) • pre-pregs • resin film infusion (lecture C 7) • thick sheet of B-stage • both systems have a limited shelf-life • usually stored in freezer to retard cure allow to warm up to avoid condensation • out-life should be recorded •

Summary • • • woven fabrics braids knitted fabrics stitched fabrics (non-crimp fabrics) bonded/felted fabrics