Interfacial evaluation and microfailure mechanisms of single fiber reinforced epoxy composites by micromechanical tests at cryogenic temperature

Abstract

Interfacial properties of composite materials at cryogenic temperatures (-150 °C) are very important factors for various practical applications in extreme environments. This paper presents the results of a study comparing the interfacial properties for carbon fiber reinforced epoxy (CFRE) and glass fiber epoxy (GFRE) at 25 to-150 °C. Micromechanical techniques in a specially-designed environmental chamber were used to compare modulus and strength in tension and compression. A micro droplet test was used to evaluate the interfacial shear strength (IFSS) between the fibers and the matrices for the different composites at both temperatures. The IFSS was generally higher at low temperature than at room temperature which is attributed to an increase in modulus of the epoxy matrices albeit it may also depend on inherent differences of the different epoxies. A comparison of the tensile strengths of the surface treated glass and carbon fiber, which was performed at multiple temperatures, indicated a dependence upon the fiber's inherent flaws and surface treatment conditions. Stress transferring mechanisms were investigated by observing the microfailure patterns after the microdroplet tests. It was concluded that toughness and modulus of epoxy as well as the fiber modulus can contribute to the final interfacial adhesion in the composites.