Improvements to the Processing and Characterization of Needled Composite Laminates

Abstract : In the present investigation novel needle-processed S2-glass laminates are fabricated and several key failure modes are characterized. Double cantilever beam testing shows that mode I fracture toughness improves up to 270% compared to non-needled baseline material. In-plane compressive strength of needled material improves by up to 475%. In plane tensile strength shows mixed results, improving by 6% for moderate volume fractions of through-thickness reinforcement (TTR) and decreasing by 6% at larger volume fractions. Double lap shear tests show that interlaminar shear strength improves as much as 17% for TTR inserted at 45 relative to the laminate plane. X-ray micro-computed tomography (micro-CT) is used to investigate the unique 3D microstructure resulting from the needling process for 90 TTR samples. The micro-CT reconstructions show that the dimensions of the disturbances of the inplane fabric are significantly smaller than those imparted by the conventional tufting or stitching processes at each penetration site. Micro-CT reveals that some penetration sites are aggregates of closely spaced neighbors, resulting from the lack of precise spatial control with the needling process used in the present research. At these aggregate locations the in-plane disturbances are roughly equal in size to those from tufting/stitching.