3-D textile reinforcements in composite materials 19 Tricot Chain Knitting Warp inlay yarns 90°-0，-45°90°+8.-45°900 4545090 Unit cell Nonwoven Knitted welt material yarn layers woo'ssaudmau'peoupoow//:dny Aq paanad WV LS:6Z:ZI I 1OZ ZZ Anur 'Aupines d 1.9 3-D knitted fabrics. 1.0 0.9 Fiber packing in yarn 0.8 0.7 0=30 Jamming 4 0.6 35 0.5 40 45° 0.4 609 0.3 75 0.2 859 0.1 0◆90° 0.0 101071051010410910210'10°101021031010510°10710 入s/1 1.10 Fiber volume fraction versus ratio of stitch-to-insertion yarn linear density (tricot stitch,K=0.75,p=2.5kg/m3,f=5 and n =0.5)
3-D textile reinforcements in composite materials 19 1.9 3-D knitted fabrics. 1.10 Fiber volume fraction versus ratio of stitch-to-insertion yarn linear density (tricot stitch, k = 0.75, r = 2.5kg/m3 , fi = 5 and h = 0.5). –45° 0° Chain Tricot 45° 45°45°0°90° Unit cell b Knitting yarns Warp inlay yarns 90° –q, –45° 90° +q, –45° 90° 0° a c Nonwoven material Knitted welt yarn layers RIC1 7/10/99 7:15 PM Page 19 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
20 3-D textile reinforcements in composite materials 1.11 3-D braided fabrics. When 0<30,jamming occurs in the whole range of yarn linear density ratio from zero to infinity..When6 is in the range of30°to4o°，the fiber volume fraction decreases with an increase in yarn linear density ratio until jamming occurs.When 0=45,the fiber volume fraction decreases with an increase in yarn linear density ratio to a minimum at about i=1,and 2102 starts to increase until jamming occurs (stitch yarn diameter,A=insert yarn diameter).When 0>60,the fiber volume fraction has the same trend 因 as when 0=45,but yarn jamming never occurs.The fiber packing in the yarns,taken as 0.75,limits the maximum fiber volume fraction in the fabric. 是马 豆 1.3.4 3-D braided fabrics 3-D braiding technology is an extension of the well-established 2-D braid- ing technology wherein the fabric is constructed by the intertwining of two or more yarn systems to form an integral structure.3-D braiding is one of the textile processes wherein a wide variety of solid complex structural shapes (Fig.1.11a)can be produced in an integral manner,resulting in a highly damage-resistant structure.Figure 1.11(b)shows two basic loom set- ups in circular and rectangular configurations [27].The 3-D braids are pro- duced by a number of processes including the track and column method (28](Fig.1.11c),the two-step method [29](Fig.1.11d)as well as a variety of displacement braiding techniques by discrete or continuous motions [30]. The basic braiding motion includes the alternate X and Y displacement of yarn carriers followed by a compacting motion.The formation of shapes is accomplished by the proper positioning of the carriers and the joining of various rectangular groups through selected carrier movements. Based on unit cell geometry analysis,Fig.1.12 shows the Vi-0 relation- ship prior to and at the jamming condition [31].The fiber packing fraction
When q < 30°, jamming occurs in the whole range of yarn linear density ratio from zero to infinity. When q is in the range of 30° to 40°, the fiber volume fraction decreases with an increase in yarn linear density ratio until jamming occurs. When q = 45°, the fiber volume fraction decreases with an increase in yarn linear density ratio to a minimum at about ls/li = 1, and starts to increase until jamming occurs (ls = stitch yarn diameter, li = insert yarn diameter). When q ≥ 60°, the fiber volume fraction has the same trend as when q = 45°, but yarn jamming never occurs. The fiber packing in the yarns, taken as 0.75, limits the maximum fiber volume fraction in the fabric. 1.3.4 3-D braided fabrics 3-D braiding technology is an extension of the well-established 2-D braiding technology wherein the fabric is constructed by the intertwining of two or more yarn systems to form an integral structure. 3-D braiding is one of the textile processes wherein a wide variety of solid complex structural shapes (Fig. 1.11a) can be produced in an integral manner, resulting in a highly damage-resistant structure. Figure 1.11(b) shows two basic loom setups in circular and rectangular configurations [27]. The 3-D braids are produced by a number of processes including the track and column method [28] (Fig. 1.11c), the two-step method [29] (Fig. 1.11d) as well as a variety of displacement braiding techniques by discrete or continuous motions [30]. The basic braiding motion includes the alternate X and Y displacement of yarn carriers followed by a compacting motion. The formation of shapes is accomplished by the proper positioning of the carriers and the joining of various rectangular groups through selected carrier movements. Based on unit cell geometry analysis, Fig. 1.12 shows the Vf - q relationship prior to and at the jamming condition [31]. The fiber packing fraction, 20 3-D textile reinforcements in composite materials 1.11 3-D braided fabrics. RIC1 7/10/99 7:15 PM Page 20 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9