Research Of The Effect Of Interface On The Mechanical Properties Of Unidirectional Fiber Reinforced Composites

It is very important to establish the association between interface and composite materials properties, as it can help realize the active design and control to the interface. This work facilitates the prediction of structure properties'transfer rules of carbon fiber reinforced composite materials in a variety of service conditions, and improves both the performance conversion of carbon fiber and composite materials properties. This work provides systemic theoretical basis and technical reserves to propel the application of carbon fiber composite materials into advanced defense and civil affairs industry rapidly, efficiently and reliably. Based on above backgrounds, this research mainly concentrates on the influence of the interface properties on unidirectional reinforced composites. Interface phase is not only a bridge between the composite reinforcement phase and matrix, but also plays a key role in reinforcing the strength of composites. In addition, the interface phases have a good influence on the physical, chemical and mechanical properties of the composites, which makes the composites possess of many unique properties.In this paper, the structure of composites is analyzed by multi-scale homogenization method, which has small periodic configuration under coupled thermo-elasticity condition. This composite structure is depicted by a macro-homogeneous and micro-heterogeneous structure. All physical parameters are expressed as the functions of microscopic coordinates and macroscopic coordinates, and are expanded into asymptotic series. Based on the perturbation method, the original problem can be caused to a microscopic finite element problem and a macroscopic finite element problem. The composites'stiffness matrix can be obtained by solving the finite element equations. Comparing with the finite element results and traditional other's experimental data, it's shown that it is effective to predict the effective properties of the composite materials by multi-scale homogenization method.Then, the influence of the interface on the transverse compressive properties of composite materials is studied. The interface is represented by a cohesion model during the damage evolution analysis. The Mohr-Coulomb plastic model is adopted to simulate the matrix because the matrix shows plastic under compression. The cohesion model is also adopted in simulating the damage evolution of interface under transverse tensile load. Fiber and matrix show extremely brittle, so it is reasonable to introduce the maximum tensile stress criterion into the user material subroutine (umat). The Murakami-Ohno damage model has been used to complete the stiffness regression of the constituents of the composites. Then, the progressive damage analysis is conducted, and the damage modes are obtained. For the research of the lateral aspect, this problem can be simplified as plane strain. The two-dimensional representative volume cell as finite element model is adopted for computing. It is reasonable to take a three-dimensional representative volume element (RVE) finite model to simulate longitudinal tensile properties. For the initial failure criterion of fiber, Hashin three-dimensional stress criterion is adopted. A single cell with a fracture fiber is used to study the mechanism of transmission of interface. This paper mainly studies the influence of the interface strength and fracture energy on the properties of unidirectional reinforced composite materials. Compared with experimental results, the reliability of the numerical results is verified.