Formability of textile preforms for composite applications. Part 1: Characterization experiments Jenny Z. Yu, Zhong Cai and Frank K. Ko Forming of textile composites is a newly developed fabrication technique which can handle complex geometry with relatively high productivity. The behaviour of textile preforms in the forming process is different from that of metallic materials. In addition to the material properties and part geometry parameters, fibre architecture plays a substantial role in determining the performance of textile preforms. In order to evaluate the formability of various textile fabric preforms, experiments characterizing the deformation behaviour of textile preforms were conducted. These tests included in-plane tension, transverse compression, in-plane shear and out-of-plane bending. Fabric preforms used in the study were plain weave, five-harness satin, eight-harness satin and angle-lock interweave. The deformation behaviour of these textile fabric preforms is directional, and strongly dependent on the fibre distribution within the fabric. Therefore fibre architecture is the dominant parameter in determining the deformation behaviour of preforms. Experimental results are useful in the evaluation of formability of textile preforms in forming processes. Keywords: textile preforms; deformation; weave structure; characterization tests NOMENCLATURE 1, EC Ef ES Et FS F, h Fabric area density or mass per unit area of the fabric (kg m-‘) Fibre diameter (m) Bending rigidity, defined experimental parameter (N m) Transverse compression rigidity, defined experimental parameter (N m- ‘) Fibre elastic modulus (Pa) Shear rigidity, defined experimental parameter (N m- ‘) Tension rigidity, defined experimental parameter (N m- ‘) Shear force (N) Tension force (N) Preform thickness (m) Interlacing density, or number of interlaces per unit area of the fabric (m-‘) Fabric sample length (m) Bending moment (N m) Transverse compression pressure (Pa) Compression ratio Compression energy, defined experimental parameter (N m - ‘) Fibre volume fraction Fabric sample width (m) Yarn number per side length of the fabric (m-7 Yarn size, or number of fibres in a yarn Interlacing angle within the fabric plane (“) Bending curvature (m- ‘) Fibre density (kg me3) Shear angle (“) INTRODUCTION Forming is a well established technology that is widely used in the metal processing industry for medium-to-high volume production with high productivity. Forming of sheet moulding compound with short fibre reinforcement into various automobile parts has been done for a long time. To use similar forming technology for continuous fibre-reinforced composites is a new challenge, since the behaviour of composites is very different from that of metallic or short fibre-reinforced materials. Recently, forming of advanced composite structures emerged as an alternative technology for producing various structural parts. While metals usually can be treated as homogeneous materials, a composite by its nature is heterogeneous. Thus, during a forming process, microstructural effects must be considered. In other words, the behaviour of the component materials, such as the fibres, has a substantial influence on the composite performance. In composite processing, forming can be applied in 0956-7143/94/02/0113-10 @ 1994 Butterworth-Heinemann Ltd Composites Manufacturing Vol 5 No 2 1994 113