Two dimensional (2D) woven, braided, knitted and nonwoven fabrics have been used for the fabrication of soft and rigid structural composite parts in various industrial areas. However, composite structure from biaxial layered fabrics is subject to delamination between layers due to the lack of through-the-thickness fibers. It also suffers from crimp which reduces the mechanical properties. Triaxial fabrics have an open structure and low fiber volume fraction. However, in-plane properties of triaxial fabrics are more homogeneous due to bias yarns. A 3D woven fabric has multiple layers and is free of delamination due to the z-fibers. However, 3D woven fabric has low in-plane properties. Three dimensional braided fabrics have multiple layers and they are without delamination due to intertwine type out-of-plane interlacement. However, they have low transverse properties. A 3D knitted fabric has low fiber volume fraction due to its looped structure. A 3D nonwoven fabric is composed of short fibers and is reinforced by stitching. However, it shows low mechanical properties due to lack of fiber continuity. Various unit cell based models on 3D woven, braided, knitted and nonwoven structures were developed to define the geometrical and mechanical properties of these structures. Most of the unit cell based models include micromechanics and numerical techniques.
Part of the book: Non-woven Fabrics