Nonlinear and dynamic compressive behavior of composites with fiber waviness

The nonlinear and dynamic behavior of unidirectional composites with fiber waviness under compressive loading was investigated theoretically and exper imentally. Uni directional carbon/epoxy composites with uniform fiber wavin ess were studied. Complementary strain energy was used to derive the materi al nonlinear stress-strain relations for the quasistatic case. Nonlinear ma terial properties obtained from shear and longitudinal and transverse compr ession tests were incorporated into the analysis. An incremental analysis w as used to predict the static and dynamic behavior of wavy composites using the basic strain rate characterization data. It is shown that under uniaxi al compressive loading, strong nonlinearities occur in the stress-strain cu rves due to fiber waviness with significant stiffening as the strain rate i ncreases. Stress-strain curves are affected less by fiber waviness under ot her loading;conditions. The major Young's modulus degrades seriously as the fiber waviness increases. It increases moderately as the strain rate incre ases for the same degree of waviness. Unidirectional composites with unifor m waviness across the thickness were prepared by a tape winding method. Com pression tests of specimens with known fiber waviness were conducted. Exper imental results were in good agreement with predictions based on the comple mentary strain energy approach and incremental analysis.