Effects of material and geometric nonlinearities on the tensile and compressive behavior of composite materials with fiber waviness

The effects of fiber waviness on the nonlinear behavior of unidirectional composites under tensile and compressive loadings have been investigated theoretically and experimentally. Unidirectional composites examined were composed of continuous fibers with sinusoidal waviness in a matrix. As a consequence of material and geometric factors, both the tensile and compressive behavior of these composites was generally nonlinear under finite deformation. Analytical models were proposed for predicting the nonlinear tensile and compressive behavior as a function of fiber waviness for three types of fiber waviness pattern: uniform, graded and localized fiber waviness. The material and geometric nonlinearities due to fiber waviness were incorporated into the models based on complementary energy density and an incremental method. Specimens with various degrees of fiber waviness were fabricated. Tensile and compressive tests were conducted on the specimens to obtain the elastic properties and behaviors of the composite materials with fiber waviness. The experimental results were in good agreement with the predictions.