Trans-scale Mechanical Properties Analysis Of Fiber-reinforced Composites Under High Strain Rates

As a lightweight structural material,carbon fiber reinforced composite materials are widely used in the aerospace field.Existing researches on the mechanical properties of materials under high-speed impact are mostly for metal materials,and the research on the mechanical properties of composite materials at high strain rates is immature,which makes it difficult to be applied to separate structures such as explosive bolt boxes in the aviation sector.In order to further apply the lightweight design of aerospace structures,the dynamic mechanical behavior of composite materials under high strain rate becomes the focus of current research.This dissertation uses a combination of theoretical analysis and trans-scale finite element analysis to explore the effects of strain rate and fiber-matrix interface strength on the stiffness and strength of composite laminates,and provide a reliable analysis method for further research on the mechanical properties of composite materials at high strain rate.The main work of this article is as follows:1.To establish the dynamic damage constitutive model of fiber reinforced resin matrix composites:In this study,based on the Maxwell constitutive model of viscoelastic material,a dynamic constitutive relationship of the resin matrix at high strain rate was developed,assuming that the fiber material properties do not change with strain rate.Subsequently,the existing meso-Hashin failure criterion is modified by the strain rate effect,and damage variables are introduced to establish a three-dimensional damage model.According to the damage of the material components,the macroscale stiffness of the laminate is reduced,and the progressive damage process of the material is conducted.2.To establish the fiber-matrix-interface three-phase rate-dependent unit cell model:Based on the dynamic constitutive relationship,a three-phase(fiber-matrix-interface)representative volume element(RVE)model was developed.Considering that fiber-matrix interface strength was affected by the strain rate,a bilinear rate-dependent cohesive model was introduced to simulate the mechanical properties of the interface.This RVE impose periodic boundary conditions,combined with the mesomechanical finite element method to obtain the stiffness performance of composite single-layer plates.Comparing to the model with the fiber-matrix two-phase unit cell model and the three-phase rate-independent RVE model,it is proved that the simulation results of the three-phase RVE model with strain rate effect is more reliable.3.To propose a trans-scale analysis method for composite materials under high strain rate:This method is based on the three-phase rate-dependent RVE model that uses the principle of superposition to complete the trans-scale analysis of the dynamic performance and response of the composite structure.The effectiveness of the method is verified by numerical examples,and the effects of strain rate and interface stiffness on the dynamic mechanical properties of CFRP laminates are discussed.The dynamic constitutive model and trans-scale analysis method proposed in this dissertation can be used to study the mechanical properties of composite materials under high strain rates.This research can provide theoretical basis for the design of composite materials structural under high strain rate conditions in engineering design,and is of significance to practical applications in aerospace and other fields.