Dynamic Behavior of Carbon Fiber Reinforced Polymer (CFRP) Composites at Higher Strain Rates

摘要

Carbon Fiber Reinforced Polymer (CFRP) composites are known to have highlyvariable modulus and strength based on fiber direction. This presents significantchallenges when attempting to identify their mechanical properties. In particular, thecomposite strength and failure envelope in multi-axial loading is expected to have acomplex nature due to anisotropy. Furthermore the heterogeneity of CFRP compositesmakes it even more difficult to model their failure modes and behavior. Theseintricacies become more pronounced at higher strain rates. In this study specimenswith varying layup, geometry, and fiber volume fractions were tested in differentloading conditions. Fiber volume fractions of the samples have been determined usingthermogravimetric analysis (TGA) in nitrogen gas environment burnout tests. Highstrain rate response of CFRP composites are of scientific and technological interest.They are used extensively in aerospace (due to their high specific strength andstiffness) which necessitates their characterization for high velocity impact. Thepolymeric resins are of course expected to demonstrate rate dependence. Thereforesplit Hopkinson pressure bar (SHPB) experiments were used to determine the highstrain rate response of CFRP composites in this study. The dependence of failurestress and strain on the strain rate was examined and summarized based on differentloading conditions, geometries and layups. The failure stress is not very sensitive tostrain rate in the range of this study, however comparisons with quasi-static data isdone to further analyze this effect. The failure strains are higher when bidirectionalspecimens are loaded in the transverse direction (normal to the plane of fibers)compared to the axial loading of the unidirectional specimens. Meanwhile it wasobserved that the failure stresses of both unidirectional and bi-directional fiberspecimens are close to each other. This has led to proposing a resin strength dominatedfailure mode for CFRP composites.