Structural parameters of fabrics influence the mechanical behaviour of fabric-reinforced composites. Weft-knitted spacer fabrics have high energy absorption capacity. In this paper, low-velocity impact behavior of composites reinforced with weft-knitted spacer fabrics has been studied using energy-balance method. The effect of fabric geometry on the impact behavior of composites was investigated. A theoretical model was generated to predict the energy dissipated through the impact, considering the structural parameters of fabrics as reinforcement of composites. For this purpose, dissipated energies due to contact, membrane and bending deformation of fabrics, and buckling deformation of spacer yarns were considered. In order to evaluate the proposed model, weft-knitted spacer fabrics with two types of spacer yarn's orientation were used as reinforcement of composites. Low-velocity impact examinations were performed using the drop hammer testing machine. The results showed that the model has about 12 and 13% error in prediction of dissipated energies of different samples. Comparison between theoretical and experimental results confirms that the proposed model is capable to predict the impact behavior of weft-knitted spacer fabric-reinforced composites.
In this study, tensile behavior of tubular braids has been studied using energy method. Tensile response of the braid is investigated in two steps:Step I, geometrical deformation of braid structure;Step II, mechanical response of the constituent yarn. In step I, the effect of geometrical deformation on the tensile behavior of braid is considered. A geometrical model is generated to obtain the structural parameters of braid in deformed state and used to build a mechanical model. In step II, the effect of mechanical properties of yarns on the tensile behavior of braid is investigated. For this purpose, a straight-line model is presented for geometry of the unit cell of 1/1 pattern braids. Based on the constituent yarn characteristics and geometrical model, a predictive model for the Young's modulus of braid is developed. Theoretical results of Young's modulus of the braid are compared to the experimental data reported in the literature. Results showed that the generated model has reasonable accuracy.
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