Comparison study of mechanical properties and damage kinetics of 2D and 3D woven composites

What is it about?

The in-plane compressive behavior of two- and three-dimensional woven composite was investigated at high strain rates. The Split Hopkinson Pressure Bar is employed to test the high strain rate dynamic mechanical properties of E-glass vinylester composite material. For three-dimensional woven composite, two configurations were tested: compression responses along the stitched direction and orthogonal to the stitched direction. Dynamic compression properties for two- and three-dimensional are determined and compared. Experimental results show that the strain rate has a significant effect on the two- and three-dimensional woven composite response. It is observed that the three-dimensional woven composite has higher compression strength and dynamic modulus than the two-dimensional composite at high strain rate. For this study, a high-speed camera was used to determine the damage kinetics under dynamic load. The two-dimensional woven composite is mainly damaged in a mode of matrix cracks and severe delamination, while the mode for three-dimensional woven composite is mainly cracking of matrix and delamination for in-plane along to the stitched direction and shear banding failure for in-plane orthogonal to the stitched direction.

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Why is it important?

2D and 3D woven composites were characterized dynamically to assess the relative advantages of 3D-stitched in high strain rate compressive loading. The compressive properties and damage mode of these composite materials are presented IP-SD, IP-OSD for 3D and in-plane direction for 2D woven composites. Also some specific conclusions drawn from the high strain rate testing of these materials are the following. • The dynamic elastic modulus, the maximum stress and strain at maximum stress for 3D specimens increase with increasing strain rate. • The 3D-stitiched woven composites have higher values of compression dynamic modulus and maximum stress for IP-SD than for IP-OSD at same strain rate. • The maximum stress and compression dynamic modulus for 2D composite increases with strain rate until a strain threshold is reached from which the tendency is reversed; i.e. they decrease with the increase of strain rate. The thermal softening due to inelastic heat dissipation and damage may explain this behavior. The photographs of the damaged composites at various strain rates in-plane directions show that the damage mode is completely different for 2D and 3D woven composite. Failure mode for the 3Dstitched composites consists of matrix/fiber failure, fiber pullout and delamination for 3D-SD, whereas for 3D-OSD, it consists of shear banding. The matrix cracks and severe delaminations are the main modes for 2D woven composites. In the some stitched samples under compression testing, the construction does not separate totally due to the binder yarn (z-yarn) reinforcement. For improving the delamination resistance of 3D-stitched composite, it is anticipated to increase the stitch density. It is noted that the addition of z-fibers into composites degrades the in-plane properties. To do that it would be necessary to find a compromise between an optimum stitch density and the in-plane mechanical properties.

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