4 Orientations in a Woven Fabric Machine direction = "warp" or "end"Perpendicular direction = "fill" or "weft" or "pick" or "woof”Frequently the warp direction corresponds with the 0°, or longitudinal directionAnd fill with the 90° or transverse directionHowever - this is not necessarily the case and should be carefully noted.
5 Woven FabricsGenerally characterized by two sets of perpendicular yarns systemsOne set is raised and lowered to make “sheds” (these are warp yarns)The other set is passed through these sheds, perpendicular to the warp yarns (these are fill, or pick or weft yarns)
6 Woven FabricsThe structure of the woven fabric is the pattern of interlacing between the warp and weft yarnsYarns can “float”, or not interlace for some distance within a woven fabric
7 Crimp in WeavesThe crimp is defined as one less than the ratio of the yarn's actual length to the length of fabric it traverses.Crimp levels influence fiber volume fraction, thickness of fabric, and mechanical performance of fabric.High crimp leads toReduced tensile and compressive propertiesIncreased shear modulus in the dry fabric and the resulting compositeFewer regions for localized delamination between individual yarns.
8 CrimpCrimp is defined as the ratio of excess length of yarn in a fabric to the length of the fabricC = ly/ lf - 1lfly
9 CrimpCrimp is determined by the texture of the weave and the yarn sizeGenerally, in weaving, the warp yarns have most of the crimp, the fill very littleThis is a direct result of the warp yarns lifting during weaving and the filling yarn being inserted along a straight path
10 CrimpVarious models of crimp exist, the most rigorous developed by Pierce in the 1930s.
11 Crimp pi = (lj – D qj) cos qj + D sin qj hi = (li – D qi)sin qi + D(1 - cos qi)ci = (li/pj) - 1h1 + h2 = d1 + d2 = DWhere pi =Thread spacing; li = Modular length; ci = Yarn crimp; di = Yarn diameter; hi = Modular height; qi = Weave angle D = Scale factor; sum of warp and weft diametersi,j = warp and weft directions.
18 Areal DensityAreal density is a measure of the weight per unit area of the fabricUsually expressed in g/m2 or oz/yd2.Areal density is a more reliable experimental metric for fabrics than thicknessAreal density can be correlated to volume fraction
19 Areal Density Areal density can be calculated as A = [l (1+Cw) nw Lw + w (1+Cf) nf Lf]/(w l)Where Ci = crimp of the i yarn, ni = number of i yarns per unit length, Li = linear density of the i yarn, w = width, l = length, and I=warp or weft.
27 Variations in Weave Design If large yarns are used in the warp direction and small yarns are infrequently spaced in the weft direction, the resulting fabric resembles a unidirectional material.Weaves can be formed with gradients in a single or double axis by changing yarn size across the width or lengthComplex shapes can be achieved through “floating” and cutting yarns to reduce total number of yarns in some section of the part
30 Issues with shaping woven fabrics Tailoring the cross-section of a woven fabric will generally result ina change in weave angle,a change in the distribution of longitudinal, weaver, and fill, anda change in fiber volume fraction in consequence to the change in thickness.Some fiber volume fraction effects can be controlled by tooling. The tailoring occurs in a discrete manner, using individual yarns, whereas most tooling will be approximately continuous.
31 Example of single taper weave Consider a tapered panel where gradation in thickness is achieved by changing yarn size/count across the width
32 Design of tapered woven panel Pick count is constant, warps and wefts per dent are modified to taperZ yarn path changes to accommodate the weave.
33 Variation in Fiber Volume Fraction This variation in yarn packing results in variations in Vf for the resulting composite.
34 Variation in weave angle The weave angle will also change throughout the width of the part due to varying warp yarn count and part thickness.
35 Yarn DistributionsThe distribution of warp, weft, and Z yarn will also vary throughout the part.
36 Variations in ModulusAll mechanical properties will vary throughout the part
37 Volume FractionVolume fraction is the percent of fiber contained within a given volume (usually the composite in question)Volume fraction can be calculated from areal densityVf = A r / tWhere Vf = fiber volume fraction, A = areal density, r = density of the fibers, and t = composite thickness
38 Process Control and Variability Processing ErrorsDamaged yarnsMisplaced yarnsSources of errorMachinery malfunctionMachinery variabilityBad control parametersPost-manufacturing deviations
40 On-line Monitoring of Manufacturing Realtime feed-back from shedding and insertion mechanismsVisual scan of fabric surfacesXray or neutron scan of fabric interiorUsing tracer yarns
41 Three Dimensional Weaving Uses "standard" weaving technologyComplexity of weave is limited by number of independent shedding devicesSome limitations on maximum thickness of fabric due to shed size and beatup limitations
42 Types of 3-D Woven Fabrics XYZLayer-to-layerThrough-thickness
43 3-D Weavingshedweaverwarpfilling insertionfabric movement
47 Components of 3-D Woven Fabrics Longitudinal yarnsParallel to warp directionWeaving yarns (web yarns)Lie in warp-thickness planeSurface weaversLocated at t=0, t=maxFilling yarnsLie in fill-thickness planeGenerally aligned with the fill direction
48 Components of 3-D Woven Fabrics 1/hpFillsLongitudinalsWeavertqSurfaceWeaverwarp
49 Physical Relationships of 3-D Woven Fabrics Vf = ∑ Wi / WcWc = (1/hp) (1/hw) tWi = mi Ai lill = (1/hp)lw = (1/hp)/cos(qw)ls = (1/hp)/cos(qs)lp = (1/hw)
50 Process Variables Yarn sizes (all independent) Reed size (limited by yarn size)Picks per inch (limited by yarn size)Weave angleNumber of filled warp positions
51 Preform Input Parameters Using fiber volume (Vf), thickness (t), ply percentages (wt%) as inputs: Here r is fiber density for each n fiber type and w is the preform areal density.Yarn spacings needed for each ith system (warp, fill, weaver) can then be found using the tow linear density N:
53 Determining Preform Thickness Requirements Tows required to meet thickness can be estimated assuming a common aspect ratio (AR):bAR=aa2db==ApabpaARA1a==d4ARpAR-42A3.910in===ainp6p6total thicknesst.100inches====tows needed for thickness11towstow thickness2a2.00455inches
54 3D Woven Preform Case Study Two sample preforms were specified, each with a 45°weave angle requested:ParameterSample 1Sample 2%0° fiber47770° fiber typeIM7-12kIM7-12k%90° fiber471790° fiber typeIM7-12kIM7-12k%z fiber66z fiber typeAS4-3kAS4-6kthickness (inches)0.1000.100Volume fraction (%)5656The preforms were procured from a weaver, then evaluated based on the design methodology.
55 Example CalculationsExample Calculations for Sample 2, using IM7-12k graphite tows for all inputs:62Fiber direction% towsdirectionalarealoz10inlbæydö:ypi=57.23ç=density2èø110.4 ypiyd25.0 lbs16 oz36 in(oz/yd2)0°7757.236æö2oz10inlbçyd90°1712.639:ypi=12.63=24.4 ypi2èøyd25.0 lbs16 oz36 inttt64.46Total10074.326æö2oz10inlbçydz:ypi=4.46cosa=7.9 ypi2èøiyd25.0 lbs16 oz36 in
56 Applying the Methodology Sample 1Parameter0°90°tttRequiredReportedRequiredReportedRequiredReportedareal weight34.934.934.9220.127.116.11(oz/yd2)yarns per inch67.567.567.56718.216Volume fraction26.422.926.418.104.22.168Sample 2Parameter0°90°tttRequiredReportedRequiredReportedRequiredReportedareal weight57.212.512.622.214.171.124(oz/yd2)yarns per inch110.42424.41108.36Volume fraction126.96.36.199188.8.131.52
58 Examining Volume Fraction from Input Parameters Evaluating Sample 2:6oz10inlbæçydö26ypi=wcos(22.5)z2èøyd11.8 lbs16 oz36 inw=1.59+57.22+12.45=71.26oz/yd2æö2lbs36 in16ozozç÷=V.064.100 in71.26f3èø2inydlbydV=53.7%fIt was calculated that 74.3 oz/yd2 was needed to meet the 56% volume fraction specified
59 Example 6 ends per inch, 6 picks per inch, 4 picks thick 12K AS-4 yarns long. & fill, 6K weavers, no surface weaversWeaver yarn ratio - rise/run =tan(qw) arThickness = 0.25 inchAll warp slots filledaspect ratio = (np mp)/t
60 Effect of Weave yarn ratio on Fiber Volume Fraction 0.750.70.654 epi6 epi0.60.55Fiber Volume Fraction0.50.450.40.350.30.252468101214Weave Angle Ratio
61 Effect of Weave Yarn Ratio on Weave Angle 7060504 ppiWeave Angle (deg)6 ppi403020102468101214Weave Angle Ratio
62 Effect of Weave Angle on Distribution Based on varying weave yarn ratio only0.8Percent longitudinal0.7Percent weaverPercent fill0.60.5Distribution Ratio0.40.30.20.151015202530354045Weave Angle (deg)
63 Effect of picks per inch on Fiber Volume Fraction 0.450.40.35Fiber Volume Fraction0.30.250.20.15246810121416Picks per inch
64 Effect of picks per inch on Weave angle 4540353025Weave Angle (deg)2015105246810121416Picks per inch
65 Effect of Weave Angle on Distribution Based on varying ppi only0.8Percent longitudinal0.7Percent weaverPercent fill0.60.5Distribution Ratio0.40.30.20.151015202530354045Weave Angle (deg)
66 Production of Complex Shaped Weaves Complex shape - complex, but uniform sectionVery complex shape - complex, nonuniform section
67 Production of Complex Shaped Weaves Consider section as consisting of rectangular piecesDevelop weave parameters for each pieceDevelop interconnection paths
68 Production of Very Complex Shaped Weaves Decompose part into rectangular and shell sectionsConsider impact of cutting yarnsConsider "folding" type operations