Tensile Impact Behavior Of Multi-axial Multi-layer Warp Knitted (MMWK) Fabric Reinforced Composites

The interweave crimp of woven fabric is a factor of influencing the tensile stiffness and strength of woven fabric and its reinforced composite because of the skewness of warp and weft yarn. Contrary to the construction of woven fabric, the warp (0°), weft (90°) and bias (±9) yarns are held together by a chain or tricot stitch through the thickness direction in multi-axial multi-layer warp knitted (MMWK) fabric. There are no crimps in warp, weft and bias yarn in MMWK fabrics. Hence the tensile stiffness and tensile strength will reach to the maximum value compared with other kinds of fabrics.The uniaxial tensile behavior of multiaxial multi-layer warp knitted (MMWK) E-glass/ epoxy composite materials along warp, weft and bias directions was investigated at high strain rates to analyze the influence of strain rate on tensile properties andfailure mode of the MMWK composites under tensile impact.The uniaxial tensile test at strain rates from 1100/s to 2200/s were conducted with the split Hopkinson pressure bar (SHPB) technique. The tensile test at quasi-static state was tested on MTS 810 system and compared with those in high strain rates.The results indicate that the failure strain and tensile stiffness are rate sensitive along warp, weft and bias direction. The failure modes of the MMWK E-glass/epoxy composites under in-plane direction loading are matrix shear failure in quasi-static state while interface failure and yarn breakage and pullout in high-strain-rate loading.The results obtained in this work enhance the understanding of dynamic properties for MMWK composites, and provide a theoretical basis for their practical applications.