Elastic and damage behavior of three-dimensional woven composites incorporating solid rods

Abstract

This articles examines the relationship between processing and performance of three-dimensional (3D) woven composites. Four types of fabrics were made with the solid rods incorporated in the axial direction. The first is a 3-axis orthogonal type having yarns in two weaving directions; the second is similar except that no beat-up is applied to the weaving yarns. The third type combines the rods in two directions. The last is a 5-axis type that adds two off-axis yarns to the first type. Both Kevlar and carbon tows were used in the rods and weaving yarns. No pressing force was applied during curing of the vinyl-ester resin to preserve the as-formed fabric configuration. Microstructures of the materials have been observed, and unit cells have been defined to model the composites. The fabric geometry model is adopted for predicting the elastic moduli. Material characterization has been carried out based on flexure and Izod impact tests. The dominant damage modes under the flexural and impact loads have been identified for each type of materials. The concept of weaker-plane that dictates material failure has been introduced for the multi-directionally reinforced composites. Weaving loops on fabric surfaces have been found to play a crucial role in the formation of cracks. Failure and the associated energy-absorbing mechanisms of the present materials have been discussed in detail.