Transverse Impact Damage And Behavior Characterization Of 3-D Multi-structured Knitted Composite Under Impulsive Loading

3-D multi-structured knitted composite is composed of warp knitted fabric and interlock knitted fabric,and stitching the two knitted fabrics along thickness direction. The multi-structured knitted composite has high in-plane stiffness and strength,good formability and de-lamination resistance.With the large deformation of yarn loop in knitted fabric,the knitted composite also has higher energy absorption under impact loading.The dynamic responses of the 3-D multi-structured knitted composite under transverse impact were investigated with a modified split Hopkinson pressure bar (SHPB) apparatus.The quasi-static indentation behavior of the knitted composite was also tested with MTS-810 material testing system.The load-displacement curves and damage morphologies were obtained to analyze the energy absorption and impact damage mechanisms of the composite under different impact velocities. A unit-cell model based on the microstructure of the 3-D multi-structured knitted composite was established to determine impact deformation and damage. Incorporated with the unit-cell model,the maximum stress failure theory and the critical damage area(CDA) failure theory have been implemented as a user-defined material subroutine(VUMAT) with FORTRAN for finite element analysis.The calculated results of load-displacement curves,energy absorption and impact damage were compared with those in experimental.The good agreement of the comparison proves the validity of the unit-cell model and user-defined subroutine VUMAT.This manifests the applicability of the VUMAT to characterization and design of the 3-D multi-structured knitted composite under other impulsive loading conditions.