Dynamic Responses Of 3D Biaxial Spacer Weft-knitted Composite Under Impact Loading And Finite Element Simulation

The impact loading often takes place during the engineering application. Since the mechanic property of composite materials under impact loading has large difference from that under quasi-static loading, it is necessary to study the impact responses of composite materials.3D biaxial spacer weft-knitted composite is a new kind of textile structural composite. Based on conventional spacer weft-knitted fabric, warp and weft yarns are inserted, which enhances tensile strength and stiffness in the in-plane direction. The connecting yarn, which connects the upper and lower layers of weft-knitted fabrics, enhances inter-laminar shear strength and prevents the slide between upper and lower layers.The responses of 3D biaxial spacer weft-knitted composite circular plate under impulsive loading with different impact velocities had been investigated both in experimental and FEM calculation. The impact tests were carried out with a modified split Hopkinson pressure bar (SHPB) apparatus and also compared with the quasi-static indentation tests. The load-displacement curves of the composite circular plate under impact were obtained to analyze the energy absorption and dynamic responses. The transmission process of stress wave in Hopkinson bar was the process of input and reflection for many times. A part of energy is absorbed by composite every time the stress wave input. It is found that both failure load and failure deformation increase with the increasing of impact velocity, and the failure along the course direction is more severe than that along the wale direction. The energy absorption of the circular plate also increases as impact velocity increasing. The main failure mechanism includes matrix spallation in rear side under impact loading while the fiber extension and pullout in quasi-static test.Based on the unit-cell model of the 3D knitted composite, a user-defined material subroutine has been developed to incorporate with commercial finite element code ABAQUS for the quasi-static and impact loading simulation. The good agreement between the experimental and FEM calculation results indicates the feasibility of the application of the unit-cell model to the engineering structures made of the 3D knitted composite.