EVALUATION OF FIBER SURFACE-TREATMENT AND SIZING ON THE SHEAR AND TRANSVERSE TENSILE STRENGTHS OF CARBON-FIBER-REINFORCED THERMOPLASTIC MATRIX COMPOSITES

The mechanical performance of advanced composite materials depends to a large extent on the adhesion between the fiber and matrix. This is e specially true for maximizing the strength of unidirectional composite s in off-axis directions. The materials of interest in this study were PAN-based carbon fibers (XA and A4) used in combination with a thermo set (EPON 828 epoxy) and a thermoplastic (liquid crystal polymer) matr ix. The effect of surface treatment and sizing were evaluated by measu ring the short-beam shear (SBS) and transverse flexural (TF) tensile s trengths of unidirectional composites. Results indicated that fiber su rface treatment improves the shear and transverse tensile strengths fo r both thermosetting and thermoplastic matrix/carbon fiber-reinforced unidirectional composites. A small additional improvement in strengths was observed as the result of sizing-treated fibers for the epoxy com posites. Scanning electron microscope photomicrographs were used to de termine the location of composite failure, relative to the fiber-matri x interface. Finally, the epoxy composites SBS and TF strengths appear to be limited to the maximum transverse tensile strength of the epoxy matrix, while the thermoplastic composite SBS and TF strengths are li mited by the LCP matrix shear and transverse tensile strengths, respec tively.