Effect of Sizing on the Interfacial Properties of Carbon Fiber Composites

Abstract

Any heterogeneous structural material has interfaces that transfer load from one phase to another through the interface thereby making it a critical constituent that affects overall performance of the material. Fiber-reinforced polymer (FRP) composite materials, such as carbon fiber epoxy composites, are excellent examples of these heterogeneous systems. The interface between carbon fiber and epoxy matrix is a key element of the carbon fiber composites that transfers load from matrix to the fibers and thus affects the performance of composites. One of the key characteristics of FRP composites is to have good interlaminar shear strength (ILSS) which is essentially a measure of the interfacial bonding between fiber and matrix. Various sizing chemistries were considered to coat the unsized carbon fiber and ILSS values were determined using short beam shear (SBS) experiments. In addition to changing the sizing formulations, a broad range of laminate thicknesses were considered for the performance evaluation of the composite laminates. There were two key findings in this work. Firstly, interlaminar shear strength measured using short beam shear has a strong dependence on the laminate thickness. Secondly, interfacial properties of composites can be significantly altered by modifying the fiber surface characteristics by means of sizing chemistries.