Simplified Structure Model And Fea Calculation On The Tensile Impact Behavior Of Co-woven-knitted Composite

Co-woven-knitted (CWK) composite is a novel3D textile structure composite, i.e., the matrix reinforced by the CWK fabric. CWK fabric combines woven and knitted structures together, where warp and weft yarns in the woven structure were inserted into the weft-knitted structure. CWK fabric shows both the structure stability of woven structure and the extensibility and formability of knitted structure. The anistropic level of the composite is controlled by the warp and weft yarn. The volume fraction of fibers can be enlarged and the tensile strength, stiffness and energy absorption of fabric reinforced composite can be increased in this novel structure. This paper reports the impact tensile behaviours of CWK composite under different strain rates and its damage mechanisms due to the special structure of CWK reinforcement. In this study, the tensile impact behaviours of CWK composite have been studied via experimentation and Finite Element Analysis (FEA) simulation. A simplified structure model was established according to the structure of the CWK composite.(1) The quasi-static and impact tests were carried with the MTS803material tester and the split Hopkinson tension bar (SHTB), respectively. The stress-strain curves were obtained through the experiment and the tensile strength, failure strain and damage fracture were analysed. The fractograph shows the differences in damage modes at various strain rates. The damage modes are fibers breakage and matrix shear failure at quasi-static rate, and fiber pull-out at high strain rates.(2) A commercial finite element analysis (FEA) software package ABAQUS was used in numerical calculation. It is difficult to establish warp and weft yarns as well knitted yarn in the same model because of the complex structure of the CWK composite. Compared with the warp and weft yarns, the path of the knitted yarn is spatial and irregular; the element number in FEA calculation will be large, which costs long time and is easy to get wrong. In order to facilitate the finite element calculation, a simplified microstructure model was established, i.e., the mechanical properties of the knitted yarns were converted to the resin and the equivalent resin is got. The stiffness matrix of the equivalent resin was derived. The equivalent resin and woven yarns can be regarded as woven composite. By combining the properties of the woven yarns and the equivalent resin, the tensile impact behaviors of the CWK composite had been calculated in a commercial finite element analysis (FEA) software package ABAQUS.(3) The stress-time curves and the damage fractures of the CWK composite were obtained and compared with those from the experiments. It was shown that the FEA and experiment results were in good agreement in the stress-time curve and the failure morphology. It was concluded that the simplified model and the methodology were suitable for the design of other kinds of hybrid-structure composite.