82 3-D textile reinforcements in composite materials LEVEL 1 UNIT CELL LEVEL 2 Block Block Block Cell 1 Cell 2 Cell i Micro Micro Micro Micro TOP-DOWN LEVEL 3 Cell1 Cell 2 Cell3 Cell 200 DECOMPOSITION LEVEL 4 Matrix Yarn LEVEL 5 Matrix Fibre 器+ 3.5 Multilevel decomposition of woven fabric composites:top-down. wos'ssaidmau'peaypoow/:dny m unit-cell block cell LEVEL1◆LEVEL2 3.6 Schematic of a hybrid twill weave unit cell (level 1)and a block cell (level 2). posite thickness D.As can be seen in Fig.3.6,we need 16 block cells to create the unit cell of a 2 x 2 hybrid twill fabric composite. Basically,each block cell is uniquely identified by four macro-cells (Fig. 3.7).That is,at each crossover point of a warp and a weft yarn,one needs two macro-cells in one layer to define the path for the warp yarn and two in the other layer for the weft yarn.However,it should be stressed that the two layers of macro-cells,which are always present in the unit cell,yield a correct description of the geometry (for example,the fibre volume fraction is correct).In order to describe a general 2-D weave geometry,a library of 108 macro-cells has been put together.Even the most complex 2-D wovenposite thickness D. As can be seen in Fig. 3.6, we need 16 block cells to create the unit cell of a 2 ¥ 2 hybrid twill fabric composite. Basically, each block cell is uniquely identified by four macro-cells (Fig. 3.7). That is, at each crossover point of a warp and a weft yarn, one needs two macro-cells in one layer to define the path for the warp yarn and two in the other layer for the weft yarn. However, it should be stressed that the two layers of macro-cells, which are always present in the unit cell, yield a correct description of the geometry (for example, the fibre volume fraction is correct). In order to describe a general 2-D weave geometry, a library of 108 macro-cells has been put together. Even the most complex 2-D woven 82 3-D textile reinforcements in composite materials 3.5 Multilevel decomposition of woven fabric composites: top-down. 3.6 Schematic of a hybrid twill weave unit cell (level 1) and a block cell (level 2). RIC3 7/10/99 7:37 PM Page 82 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:30:11 AM IP Address: 158.132.122.9