Analysis and Modeling of Plain Knitted Fabric Reinforced Composites

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Abstract
This paper presents the analysis and modeling of elastic properties of plain knitted fabric reinforced composites. Knitted fabric is formed by interlocking of looped yarns. Knitted fabric composite is heterogeneous with impregnated curved yarns and resin rich regions. Firstly, the three-dimensional orientation of yarns was expressed in terms of known parameters of the knitted fabric; these parameters are course density, wale density and impregnated yarn diameter. An analytical model named "cross-over model" has been proposed. This model considers the crossing over of yarns of adjacent loops at the interlocking region. The average effective elastic properties of each curved yarn were determined using the stress-strain relations for a lamina of arbitrary orientation. Using classical lamination theory, the effective elastic properites of the yarns in the cross-over model were determined. Finally, the elastic properties of the composite were determined by combining the effective elastic properties of the curved yarns and the resin rich regions. It has been shown that the cross-over model provides a rough estimate of the elastic modulus of the knitted fabric composite (volume fraction of fibers, Vf = 9.5%) by comparing theoretical predictions with the experimental results. However, it is to be noted that at higher Vf, the geometry of knit loop would be distorted thus the model accuracy would be affected.