Nonlinear and dynamic compressive behavior of composites with fiber waviness

The nonlinear and dynamic behavior of unidirectional composites with fiber wariness under compressive loading was investigated theoretically and experimentally. Unidirectional carbon/epoxy composites with uniform fiber waviness were studied. Complementary strain energy was used to derive the material nonlinear stress-strain relations for the quasi-static case. Nonlinear material properties obtained from shear and longitudinal and transverse compression tests were incorporated into the analysis. An incremental analysis was used to predict the static and dynamic behavior of wavy composites using the basic strain rate characterization data. It is shown that under uniaxial compressive loading, strong nonlinearities occur in the stress-strain curves due to fiber waviness with significant stiffening as the strain rate increases. Stress-strain curves are affected less by fiber waviness under other loading conditions. The major Young's modulus degrades seriously as the fiber waviness increases. It increases moderately as the strain rate increases for the same degree of waviness. Unidirectional composites with uniform waviness across the thickness were prepared by a tape winding method. Compression tests of specimens with known fiber waviness were conducted. Experimental results were in good agreement with predictions based on the complementary strain energy approach and incremental analysis.