FRP Composite Compressive Strength and Its Dependence upon Interfacial Bond Strength, Fiber Misalignment, and Matrix Nonlinearity

Abstract

The uniaxial compressive strength of fiber-reinforced polymer (FRP) com posites is a very complex issue which is still not fully understood. Although FRP compos ites characteristically possess excellent ultimate and fatigue strength when loaded in ten sion in the fiber direction, compressive properties are typically not as good. This behavior is due to the fact that while tensile properties are fiber dominated, compressive properties are dependent upon other factors such as matrix modulus and strength, fiber/matrix inter facial bond strength, and fiber misalignment. An analytical model of fiber microbuckling within a polymer matrix has been developed for the purpose of investigating the micro mechanical relationships between compressive strength and fiber microbuckling deforma tion, fiber volume fraction, matrix nonlinearity, interfacial bond strength, and initial fiber curvature. The results for this study provide insight into the micromechamcs governing the uniaxial compressive behavior of FRP composite materials. Results indicate that when both normal and shear interfacial stresses are considered, extension mode microbuckling is actually never the favored low energy mode of microbuckling. Results also demonstrate that depending upon material properties, service environment, and processing (fiber mis alignment), the fiber, the matrix, or the fiber/matrix interface can be the material compo nent initiating compressive failure.