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.

The aim of this paper is to develop an analytical model to predict indentations of the impactor on the composites reinforced with weft-knitted spacer fabric using Hertz contact law. For this purpose, simply supported rectangular plate with partially load developed by Timoshenko was applied to analyze the deflection of top face, and the concepts of the buckling of initially curved struts were used to find the buckling of Z-fibers. To evaluate the accuracy of the model, the effect of the number of Z-fiber per unit area and elastic modulus of Z-fiber were investigated. The results showed that in the outside the contact area, the impact force bends the layer and causes the Z-fibers to buckle, but no indentation occurs. Inside the contact zone, the indentation has occurred, in addition to the layer deflection and Z-fiber buckling. Also, indentations in both X and Y directions decrease by increasing the Z-fiber density. In addition, the higher the z-fiber modulus leads to fewer indentations. Decreasing the angle coefficient of Z-fibers leads to increase their buckling resistance. Moreover, a reasonable agreement was observed between theoretical and experimental results; so that the maximum error of prediction was less than 20%. Furthermore, the proposed model can give the indentation of different points of sandwich-structured composites according to their coordinates.