Study On Prediction Of Mechanical Performance For Unidirectional Composite Considering Interphase

Carbon fiber reinforced plastic composites (CFRP) has been widely used in many kinds of structures due to their excellent mechanical performances. These excellent macro performances are mainly controlled by the mechanical properties of micro components. Thus, it is especially important to understand the micro mechanical properties of composite detailly for fully inspiring its macro mechanical properties. With the development of experimental techniques, interphase existing between fiber and matrix has been deeply understood gradually. Recently, it appears a new research area in which composite is optimized by considering the effect of variation of the interphase properties. Based on this background, it has an important significance to establish model to valuate the mechanical properties of composites with interphase for composites optimization.For unidirectional CFRP with interphase, this paper establishs a set of performances prediction methods, such as stiffness, CTE and strength etc. Meanwhile, the elastic and damage until failure modes of the composites are given with the increase of external load. The effects of interphase are considered in detail in the micromechanical models. Overall, the main contents of this paper are provided as follows:1. Stiffness prediction. Stiffness properties of the composites are predicted by the analytical and finite element methods. Unidirectional fibrous reinforced composites are considered as transverse isotropic materials, which have five independent parameters in the stiffness matrix. The analytical and finite element methods were applied to predict these five independent parameters. In the analytical method, the Mori-Tanaka method based on Eshelby equivalent inclusion theory was used twice to evaluate the stiffness of the composites. In the finite element method, composite was simplified to a representative volume element (RVE). Then, five independent parameters were obtained after linear elastic analysis. The result was verified by experimental results. At last, the Mori-Tanaka method was used to analyze the influence of interphase parameters.2. Thermal elastic properties prediction. In this paper, thermal elastic analysis includes thermal residual stress analysis and the prediction of macro equivalent coefficient of thermal expansion. Fiber composite is simplified as an axisymmetric cylinder model containing three phases: fiber, interphase and matrix. Elastic equations with boundary conditions were established to get the residual stresses. The analytical results are well agreement with the finite element results. The sub-increment method was used to overcome the fact that epoxy properties change with temperature, and it was verified by single carbon fiber resistance experiment. Based on the cylinder model, macro equivalent CTEs of the composites were predicted and verified by experiments. Then, the influence of interphase parameters on macro CTEs was analyzed.3. Strength prediction. This paper mainly discusses the composite longitudinal tensile strength and transverse strength. According to discrete distribution of carbon fiber tensile strength, different methods were used to predict the longitudinal and transverse strength. In longitudinal direction, the Monte Carlo method was applied to conduct progressive damage analysis. There are three factors, including residual stress, stress transfer and fiber breakage, which are required to be considered in the model. The analysis was conducted iteratively until all fibers were broken, and the longitudinal tensile strength was obtained. The result was verified by macro experiments. In transverse direction, interphase debonding and matrix crack are the main failure modes. The explicit finite element was used to analyze the progressive damage process until ultimate failure. The geometric microstructure obtained by SEM or elastic collision model was imported into Abaqus. The transverse tensile or compressive strength was obtained by the progressive damage analysis. The result was also verified by experiment as well. At last, the influence of the interphase parameters on macro strength was analyzed.These mechanical performance prediction methods in this paper can also be applied to analyze for many other composites to establish the relationship between the micro component parameters and macro performances.