This article establishes a reliable constitutive model to describe the behaviors of fiber-reinforced polymer composites under quasi-static and dynamic loading. This model integrates the contributions of all the three phases of a composite: the fiber, the matrix, and the fiber/matrix interphase, which make it capable of capturing the key micromechanical effect of the interphase on the macroscopic mechanical properties of composites. The interphase is taken as a transversely isotropic material together with the fiber. By analyzing glass/epoxy and carbon/epoxy composites, it was found that the model predictions agree well with the experimental data and the model is more effective particularly when the fiber volume fraction is high. The dynamic three-phase model was also established by using the coupling of the elastic and Maxwell elements for the viscoelasticity of the matrix as well as the interphase. The article concludes that the three-phase model with consideration of the interphase influence can precisely characterize the static and dynamic mechanical properties of a FRP composite.

Most fatigue failures in aeronautical structures occur at fastened joints due to stress concentration (SC). Since more and more advanced composites are applied in aircrafts instead of conventional alloys, SC in CFRP composite plates with zigzag-arranged multiple holes has been investigated by finite element method in this paper. It is found that the static SC factor (SCF) of CFRP plates varies with the dimensionless bore and zigzag angle by a greater change than isotropic plates, and that the dynamic response amplitude and frequency of the SCF depend on the dimensionless bore and the dimensionless wave number related with material properties and the exciting frequency.