Fabrication And High Strain Rate Compression Behavior Of 3D Orthogonal Woven Composites

The vast differences in strength, ultimate strain and modulus during high strain rate deformation of materials have been a very long-standing subject of engineering interest. This thesis deals with characterization of mechanical properties of 3D orthogonal woven hybrid composites. The focus of this study is to compare the mechanical properties of these composite materials at high strain rates and quasi-static conditions and to find out the effects of failure modes on high strain rate mechanical properties of these materials.The 3D woven hybrid perform construction was evaluated: warp and Z yarns used Twaron fibers, fill yarns used glass fibers. The preforms were fabricated on the computer-controlled, fully automated, 3D weaving machine developed at The College of Textiles, Donghua University. The preforms were consolidated in epoxy matrix with the VARTM method. The static compression tests were tested using MTS servo-hydraulic machine which obtained the strain rates of about 0.001s~-1. Split Hopkinson Pressure Bar (SHPB) apparatus is used for the HSR testing of materials at varying strain rates, varying from 900s~-1 to 3200 s~-1. The specimens were tested in three directions such as warp, fill and through-the-thickness direction. Failed specimens are consequently observed under optical microscope in order to understand the fracture modes of these materials.The results of the tests on materials demonstrate considerable increase in peak strength and the elastic modulus under high strain rate in any direction. It is also observed that the failure strain values vary considerably with increasing strain rate in three directions. Because the material use different fibers in fill and warp direction, in the fill direction, the specimens showed higher strength and stiffness. In the through-the-thickness direction, there existed higher failure strain. At the same time, in the warp direction, the Twaron fiber show lower sensitivity to strain rate than the E-glass fibers in the fill direction. The damage modes of fill and warp direction are kink band deformation, matrix crack, fiber broken and declamation. In the through-the-thickness direction, the damage modes are shear deformation, matrix crack and fiber breakage. These results are essential for conducting realistic numerical simulations for safe design of structures.