Research On A High-Fidelity Unified Macro- And Micro-mechanics Constitutive Model And Its Applications For Composites

The composite structures will be broadly used in the next generation aeroengine. A high-fidelity unified macro- and micro-mechanics constitutive model and its applications for composites are studied to satisfy needs of analyzing mechanical behaviors of composites and structures on macroscopic and microscopic scales. A multi-scale finite element stress analysis corresponding to the constitutive model is developed. The method can be applied to engineering practice and possesses great importance in theory. An efficient implementation of the Generalized Method of Cell(GMC) effectively replaces the subcell strains by the subcell interfacial tractions as the basic unknown micro-variables, which in turn substantially reduces the size of the system of equations for the determination of these micro-variables. This substantial reduction in the size of the system of equations for the unknown micro-variables makes possible the analysis of repeating unit cells containing thousands of subcells, which could not be analyzed previously by the original formulation of GMC. The thermal expansion coefficients of composites have been analyzed in the paper. The results indicate that the influence of fiber shape and packing arrangement can be considered. The efficient implementation of GMC can be extended to the three dimensional GMC. It is used to predict mechanical behavior of particulate reinforced metal matrix composites. The results indicate that GMC accurately predicts the engineering properties of the particulate reinforced composites studied. The high-fidelity GMC is presented through introducing the higher-order displacement field. The model overcomes shortcomings of the absence of so-called shear coupling. The efficient reformulation of high-fidelity GMC is presented based on the hypothesis of periodicity in composite microstructure. In this approach, surface-averaged quantities are the primary variables that replace the coefficient of the displacement after the mechanical equations are analyzed and answered in microscopic elements. It reduces the number of equations involved and eliminates the concept of generic cells. The transverse and longitudinal variables are dis-coupled. The effective moduli and local stress fields are analyzed. Numerical results based on this model agree well with the available results from experiments and theoretical analysis. A unified macro- and micro-mechanics analysis multi-scale finite element method for composite structures is developed. The software for computes have been developed by integrating the model into the general finite element method program. Not only the method can consider micro-structural geometry effects on macro-properties, but also it can obtain both macroscopic and microscopic stress and strain fields, which provide sufficient basis for the damage and fracture analysis of composite structures. The ring is analyzed with the developed software. The validity of the model is verified by the result. It's significant to applying composite structures in the next generation aeroengine.