Schematic construction of carbon fiber tow microstructure models and their effect on tensile strength of carbon fiber tow/epoxy composites: Quantification of carbon fiber distribution, misalignment, and interlacing

Abstract

Carbon fiber reinforced polymers (CFRPs) are increasingly being used in cutting-edge technologies, thus rendering accurate material characterization essential. However, the unexpected microstructures of carbon fiber (CF) tows, such as random fiber distribution, misalignment, and interlacing, degrade the mechanical properties of CFRPs and render them unpredictable. Hence, the microstructures of CF tows and their effect on the performance of CFRPs must be investigated.Herein, we propose a framework for quantifying the microstructural parameters of three types of T700 grade CF tows and investigate their effects on the tensile strengths of CF tows and CF tow-reinforced composites. CF cross sections are analyzed via microscopy to measure the fiber distribution and misalignment with respect to the location. A two-roll mill experiment is designed to evaluate fiber interlacing by compressing the CF tow in the thickness direction. The tensile strengths of CFs, CF tows, and CF tow-reinforced composites are measured, whereas their interfacial shear strengths are obtained via a micro-droplet test.Two CF tow microstructure models are proposed: the uniform distribution model with a low degree of fiber misalignment resulted in a higher tensile strength ratio of CF tow compared to the core-shell model, as well as a higher tensile strength of CF tow/epoxy composites. Results indicate that the microstructure of the CF tow significantly affects the properties of the composite materials. Therefore, utilizing the framework proposed herein as a tow design parameter is expected to fulfill the varying requirements of important properties in composite material design based on the application field.