Abstract: In this paper, compressive behaviors of bi-axial warp-knitted (BWK) composite under impact loading at various strain rates were investigated. The stress vs. strain curves and the relevant failure modes with different compressive loading strain rates in three orthogonal directions were obtained from the test system of Split Hopkinson Pressure Bar (SHPB) and MTS test machine. The results indicated that the biaxial warp-knitted (BWK) composite was strain rate sensitive. The failure stress and the compressive modulus were increased with the increasing of strain rate while the failure strain was decreased. With the increase of the strain rate, the damage is more serious and failure mode is clearer. In addition, the compressive properties along the out-plane direction was much better than those of the in-plane direction. Differences of compressive properties were also observed between the warp direction and the weft direction. Thus, the composite was verified to be anisotropic. The photographs of the damaged composites at various strain rates showed that at out-plane direction the main failure mode was the interlaminar shear failure, while at in-plane direction the delamination was the main failure mode except the shear failure at quasi-static compression. This paper provides a better understanding of the failure mechanism of bi-axial warp-knitted (BWK) composite.

Key words: bi-axial warp-knitted (BWK) composite, split Hopkinson pressure bar (SHPB), strain rate, compressive loading