Theoretical And Numerical Study On Interface Damage And Effective Modulus Of Random Short Fiber Composites

Random short fiber reinforced composites have broad prospects in the field of construction,and the prediction of their macroscopically effective properties is a hot issue in this field.Predicting the macroscopically effective properties of random short fiber composites by numerical simulation methods has the advantages of cost savings and accurate calculation.With the development of finite element software and the improvement of computing power,numerical simulation methods will be more widely used.Interfacial damage debonding is an important form of short fiber composite failure.This paper aims at developing a theoretical model of a unit cell considering interface damage and debonding as well as realizing the damage debonding of random short fiber composites through numerical simulation methods.On this basis,the influence of parameters such as aspect ratio,volume percentage and interface stiffness on the macroscopic effective modulus is studied.This paper introduces the cohesive model into the shear lag theory,derives the interface shear stress distribution and fiber normal stress distribution in the elastic and damage stages,and gives the calculation formulas for the critical damage load and critical debonding load.The key steps of numerical simulation are the obtainment of cohesive parameters at the interface and the development of three-dimensional representative volume elements(RVE).Interfacial cohesive parameters were obtained by fitting the theoretical formula with the experimental results of Raman spectroscopy.The inter-fiber distance calculation method in the random adsorption algorithm(RSA)is improved to avoid crossing in extreme cases.Combined with the random adsorption algorithm and the ABAQUS dynamic explicit solver,a higher volume rate finite element model is generated.For random oriented short fiber composites,an improved explicit formula based on the Halpin-Tsai formula is proposed,which can be directly used to calculate the effective properties of random short fiber composites considering the fiber aspect ratio in the case of a perfect interface.A comparison between the theoretical prediction results and simulation results was made,it was found that the modified formula can predict the overall effective modulus well.Through the finite element simulation method,the influence of the interface and the aspect ratio on the effective modulus in the axial and transverse directions of the single fiber representative unit was studied.The relation between critical aspect ratio and critical interface stiffness was built to judge the reinforcing effect of fiber on effective modulus.A Python script was written according to the RSA,and a finite element model of random short fiber RVE was generated parametrically,and a novel interface mesh method was adopted to introduce cohesive interface into the random short fiber composite RVE,and the displacement boundary was realized.Under the conditions of fiber interface damage debonding.The effective modulus and interface damage under different interface parameters,aspect ratio and volume percentage were studied.The simulation results show that the aspect ratio has an obvious effect on effective modulus at the elastic stage,while the volume percentage has an obvious effect on effective modulus at damage stage.The interface stiffness has a significant influence on the effective modulus of the material,and the weak interface has a weakening effect on the effective modulus of the overall material.