FRP composite compressive strength and its dependence upon interfacial bond strength, fiber misalignment, and matrix nonlinearity

The uniaxial compressive strength of fiber reinforced polymer (FRP) composite is a very complex issue which is still not fully understood. Although FRP composites characteristically possess excellent ultimate and fatigue strength when loaded in tension 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 interfacial bond strength, and fiber misalignment. An analytical model of fiber microbuckling within a polymer matrix has been developed for the purpose of investigating the micromechanical relationships between compressive strength and fiber microbuckling deformation, fiber volume fraction, matrix nonlinearity, interfacial bond strength, and initial fiber curvature. The results from this study provide insight into the micromechanics governing 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 misalignment), either the fiber, matrix, or fiber/matrix interface can be the material component initiating compressive failure.