Geometrical and material nonlinear properties of two-dimensional fabric composites

The formerly developed nonlinear analysis of fabric composites is expanded to include longitudinal hardening in unidirectiona l carbon/epoxy composites and the deformed state in single-layer plain-weave composites. A simple constitutive equation is proposed to describe the hardening property. The full material nonlinear solution of the 8H satin carbon/epoxy system is in favorable agreement with the experimental results. It is confirmed that this material property is crucial in predicting a macroscopic behavior of fabric composites if warping is fully suppressed. An iterative procedure of the geometrical nonlinear analysis accounting for the warping is developed. The predicted stress-strain relations and warping coincide very well with the corresponding experimental results of carbon/epoxy plain-weave composites. The warping contributes greatly to the apparent hardening of this material at low stress levels. Nomenclature Ajj(x)9A jj = local and averaged in-plane stiffness afj (x) ,dfj = local and averaged in-plane compliance a* * = in-plane compliance in the warping-free state a - width of a thread au _ = length of a crimp part Bij(x),BiJ = local and averaged bending/stretching coupling stiffness bfj (x) ,b*j = local and averaged bending/stretching coupling compliance DIJ (x) ,Dij = local and averaged bending stiffness d*j(x),dfj = local and averaged bending compliance h = thickness of a fabric composite plate h j (x) = shape function of thread crimp h2 (x) = shape function of a warp section ht —