Shear Behavior of 3-D Biaxial Spacer Weft Knitted Composite under High Strain Rates

The punch shear behavior of 3-D biaxial spacer weft knitted E-glass/ vinyl ester composite was investigated at quasi-static (0.01/s) and high strain rates ranging from 1200 to 3200/s in wale and course directions respectively. The quasi-static shear behavior was tested on a MTS 810.23 material tester and was compared with high strain rate shear behavior from a modified split Hopkinson pressure bar (SHPB) technique. The experimental results indicate that the shear stiffness, failure stress, and failure strain are rate sensitive both in wale and course directions. The shear stiffness and failure stress increase with the the increase of strain rate. The failure strains along the wale and course directions decrease with increasing strain rate. Furthermore, the shear failure becomes more severe in the course direction than in the wale direction at high strain rates. The damage mode in the wale direction at various strain rates is punch shear failure, while that of the course direction is filament tow breakage and matrix cracks. The unique features of this article are to conduct the punch shear tests at high strain rates successfully using a modified SHPB apparatus for the novel 3-D knitted composite and find the strain rate sensitivity both in shear behavior and failure mode. The results will benefit the structural design of the 3-D knitted composite owing to the higher in-plane tension stiffness and strength of the composite than any other 3-D textile structural composites.