The Influence of the Fiber/Matrix Interface on Local Glass Transition Temperature

Abstract

Determining the local structure and properties of the interphase is crucial to understanding how the interphase influences overall thermo-mechanical behavior of a composite. Several theoretical investigations have presented evidence for the existence of an interphase region with a glass transition temperature that is significantly lower than that of the neat resin. In the current study both interferometric measurements and single fiber critical length tests are performed on samples with tailored interphases to further investigate variations in local glass transition temperature and its influence on micro-mechanical behavior. Two different interphase conditions are considered: fibers coated with a low Tg resin and untreated fibers (no coating). Micro-interferometry was utilized to study differences in thermally induced axial displacements for the two different interphase conditions. Additionally, single fiber critical length tests were performed over a range of temperatures to determine the effects of the interphase glass transition on the value of interfacial shear strength. Experimental results support the existence of a reduced glass transition temperature near the fiber surface.