Effects of porosity and edge reinforcements on interlaminar tensile strength of curved-beam carbon fiber composites

Abstract

Fiber-reinforced composites are orthotropic with excellent strength in the fiber direction; however, they are susceptible to early failures in the orthogonal direction due to defects and delamination. This poses the threat of a significant impact by reducing the interlaminar tensile (ILT) strength of fiber-reinforced composites. In addition to service loads on composite parts and environmental factors, free-edge effects and porosity are major contributors to the premature failure of composite parts. Free-edge effects are caused by microcracks and Poisson’s mismatch on the machined edges of a composite part, while porosity is the result of entrapped air during composite manufacturing. This work is aimed at improving the ILT strength of a 90^o curved-beam composite by suppressing failure due to free-edge effects and porosity. This is achieved by providing reinforcements at the machined edges. Aluminum alloy sheets and glass pre-impregnated (prepreg) composites were used to reinforce the composite curve beams to evaluate the correlation between ILT strength and porosity of the curved-beam laminate. Strength tests were performed using the ASTM D 6415 four-point bend test. Test results indicate that the increasing porosity from 0.49% to 4.75% in the fiber-reinforced curved-beam composites drastically reduced their strength (over 47%), while the composite edge reinforcements improved their strength by 25%. This study will be useful for the future design and manufacture of curved-beam composites in different industries, such as defense, aircraft, helicopter, drone, wind turbine, ship and automotive.