Compressive response and failure of fiber reinforced unidirectional composites

The compressive response of polymer matrix fiber reinforced unidirectional composites (PMC's) is investigated via a combination of experiment and anal ysis. The study accounts for the nonlinear constitutive response of the pol ymer matrix material and examines the effect of fiber geometric imperfectio ns, fiber mechanical properties and fiber volume fraction on the measured c ompressive strength and compressive failure mechanism. Glass and carbon fib er reinforced unidirectional composite specimens are manufactured in-house with fiber volume fractions ranging over 10 similar to 60 percent. Compress ion test results with these specimens show that carbon fiber composites hav e lower compressive strengths than glass fiber composites. Glass fiber comp osites demonstrate a splitting failure mode for a range of low fiber volume fractions and a simultaneous splitting/kink banding failure mode for high fiber volume fractions. Carbon fiber composites show kink banding throughou t the range of fiber volume fractions examined. Nonlinear material properti es of the matrix, orthotropic material properties of the carbon fiber, init ial geometric fiber imperfections and nonuniform fiber volume fraction are all included in an appropriate finite element analysis to explain some of t he observed experimental results. A new analytical model prediction of the splitting failure mode shows that this failure mode is favorable for glass fiber composites, which is in agreement with test results. Furthermore, thi s model is able to show the influence of fiber mechanical properties, fiber volume fraction and fiber geometry on the splitting failure mode.