Towards Automatic Designing of 2D Biaxial Woven and Braided Fabric Reinforced Composites

Abstract

This paper presents a general methodology to automatically analyze the stiffness and strength of a textile composite reinforced with any 2D (twodimensional)biaxial woven or braided preform only using its constituent fiber and matrix properties and limited number of independent textile geometric parameters. The textile composite under consideration can be subjected to an arbitrary load condition. Based on the assumption of a perfect contact between the fill and warp yarns and a microphotographic observation, a geometric model is developed to describe the yarn architecture of the 2D biaxial woven or braided fabric structure. The textile composite is eventually subdivided into small elements, each of which is considered as a unidirectional (UD)fibrous composite in its local coordinate system. The bridging micromechanics model is applied to determine the 3D mechanical properties of the UD composite at each load level up to failure based on the information of the current constituent properties and the fiber volume fraction. The matrix properties have been defined according to the averaged value of the current three principal stresses in the matrix. If this value is positive, the properties obtained from a tensile experiment should be used; otherwise, those from a compression test are employed. This is because the matrix material in the textile composite is usually subjected to 3D stress state, and is because a polymer matrix generally has different properties in a uniaxial tension from those in a uniaxial compression. The resulting properties of all the UD composites are assembled by means of a volume average based on either iso-strain or iso-stress approach, to give the overall stiffness and strength of the textile composite. One significant advantage of the present method is that only minimal input data are required, which can be easily measured before composite fabrication or taken as designing variables. Thus, an automatic design for the required properties of a textile composite can be achieved. Applications have been made to those composites reinforced with plain, 5-harness and 8-harness satin weaves and diamond and regular braids. While limited test results for the woven fabric composites are available from the literature, an extensive experimental program has been carried out to measure stiffnesses, strengths, and stress–strain curves of the braid composites under uniaxial tensile load. Two different material systems, i.e., glass/epoxy and carbon/epoxy systems, each with three different braiding angles have been studied. It has been found that the iso-strain assemblage scheme gives grossly better correlation for both the stiffness and strength of all the composites with the experiments.