Research On Mechanical Behaviors Of Filament Wound Composite Considering Fiber Crossover And Undulation

The fiber bundle in one direction interweave with the fiber bundle in the other direction during the filament winding process,thus produce fiber crossover and undulation in the architecture of the filament wound composite.Those fiber crossover and undulation will cause local stress/strain concentration,also increase the likelihood of other manufacturing related defects such as voids,resin-rich areas,therefore,the region with fiber crossover and undulation often becomes the birthplace of fracture initiation,and have a great influence on the failure(leakage)and damage of the filament composite structure.Considering fiber crossover and undulation,the following aspects are studied about the damage and failure of filament wound composite structure in this paper:Prediction of effective elastic properties of filament wound composite,Stress feild and damage analysis of the repeated unit cell of filament wound composite,Buckling analysis of thin-walled filament wound structure,Failure and damage analysis of filament wound composite structure,curing process and residual stress analysis of filament wound composite structure.The main work and research results of this paper are as follows:1.Aim at fiber crossover and undulation,the meso-structure of filament crossover and undulation is described by using several meso-parameters such as fiber orientation,fiber inclination angle,resin rich area and fiber volume fraction and bundle cross section.With this meso-stmcture model and the classic laminate theory,a method for calculating the stiffness of filament wound composite is eventually established.The numerical results show that the elastic moduli is not constant due to the fiber volume fraction in fiber crossover region is different,In the rich resin region,the elastic modulus and shear model decrease more obviously,while the poisson ratio increases.2.On the basis of meso-stmcture model for fiber crossover and undulation,meso-scopic model for the repeated unit cell of filament wound composite is established,with this meso-scopic model,periodic boundary condition,damage failure criteria and material degradation rules,a meso-scale repeated unit cell damage failure model for filament wound composite is established.The stress distribution of repeated unit cell,the stress concentration caused by the fiber crossover and the failure damage process and ultimate strength of repeated unit cell are analyzed.The numerical results show that the distribution of stresses is uneven in the repeated unit cell,the stress concentration coefficient in fiber crossover region is large than it in laminate region,the initial damage of the fiber and matrix emerge in the fiber crossover and undulation region.3.The buckling analysis model for filament wound composite cylindrical shell consider fiber crossover is established to study the buckling load varies with the winding angle,thickness to diameter ratio and length to diameter ratio,also investigate the influence of fiber crossover and undulation on the buckling behavior of filament wound composite.The calculate results show that the buckling load and buckling mode of the filament wound composite shell are closely related to the winding angle,length to diameter ratio and winding number In some specific cases,such as the winding angle in the range of 10°-30°,small length to diameter ratio or multi-layers,the crossover and undulation of fiber bundle have a significant effect on the buckling load.4.A macro-meso analysis model is proposed to investigate the effect of fiber crossover and undulation on the failure of filament wound composite.The basic analysis steps as follows:The filament wound composite structure is considered to be composed of two different parts:fiber crossover area and laminated area,and the corresponding elastic parameters are given to different regions,the macro stress-strain distribution of filament wound composite is calculated first;then the macro-meso stress conversion matrix of fiber crossover region is calculated,and convert the macro stress into meso stress;Finally,the failure condition and process of laminated region are determined by the macro stress calculated at first step,and the failure process of fiber crossover region is determined by the meso stress calculated at second step.Based on this macro-meso analysis model,a user defined material subroutine(UMAT)is written to calculate and analyze the influence of fiber crossover and undulation on the stress/strain distribution,strength and failure process of the filament wound composite.5.The failure process of filament wound composite cylindrical shell and pressure vessel under different loads(axial tension/compression,internal pressure,external pressure and transverse load)are studied by numerical calculation,The numerical results indicate that:The strain in the same winding layer is not evenly distributed,and the strain in fiber crossover region is obviously bigger than it in laminate region under axial tensile/compressive load and internal pressure.The exist of fiber crossover and undulation lead to reduce the strength of filament wound composite structure.Under different loads condition,the failure process of filament wound structure is different.In the case of axial tension and internal pressure load,the matrix failure occurs first in the fiber crossover area,and then extends gradually to the laminated area.In the case of axial compression,when the winding angle is less than 45°,the failure position is mainly located at the helical fiber crossover and undulation area,and the hoop fiber crossover and undulation region is the failure position of structure with winding angle more than 55°.6.Using the Fourier heat conduction equation and the curing kinetics equation of matrix,considering the changes of thermal and mechanical property of composite and curing shrinkage of matrix during the curing process,the curing process and residual stress model for filament wound composite structure were established,Based on this model,the subroutine UMAT,UEXPAN and HETVAL are written to describe the mechanical constitutive model,the thermochemical strain of the composite and the exothermic reaction of matrix during the curing process respectively,and study the residual stress produced during the curing process.The calculate results show;the curing process temperature has a significant effect on the temperature Field and curing degree of filament wound composite;the residual stress in the filament wound structure has a dose relationship with the winding angle,the number and the thickness of winding layer;the fiber crossover have little effect on the residual stress.