Permeability And Compressibility Of Woven Fibrous Reinforcement

Liquid Composite Molding(LCM)is one of the most common composites manufacturing processes.Compared to the particle reinforcement and the short fiber reinforcement,the woven fibrous reinforcement possesses outstanding mechanical properties,thus it is widely used in LCM processes for high-performance composites manufacturing.Although even with continuous optimization of the processes after decades of development,the defects still remain in the final composite parts.One of the most essential reasons is that the textile has a special meso-microscopic scale architecture,which causes enormous difficulties to the analysis of several key procedures in LCM,such as the saturation and the compaction.More specifically,there exist several key issues: 1)The woven textiles have mesoscopic pores and microscopic pores,leading to different flow behaviors.Subsequently,the resin velocity at the flow front is not uniform in the saturation process,and air may be entrapped to form air bubbles,which induces defects in the composite products.2)The mechanical properties of the textiles relate to the mesoscopic fiber tow,and the deformation of the fiber tow at the mesoscopic scale relies on the displacement and the deformation of the fiber filament at the microscopic scale.This multi-scale structure makes it hard to describe the mechanical behavior of the fiber tow with the general constitutive relations.Therefore,the compressibility of the textiles is hard to predict.3)One lacks an effective tool and approach to precisely construct the mesoscopic or microscopic geometric models of textiles.Thus it is difficult to conduct a comprehensive and detailed analysis on the mechanical behavior of the textiles at the meso-microscopic scale.The current thesis aims to establish a toolkit at the meso-microscopic scale to conduct a comprehensive analysis on the permeability and compressibility of the woven fibrous reinforcement,with the Micro computed tomography(Micro-CT),the experimental measurement and the numerical simulation.To that end,first the microstructural and mesostructural geometrical modeling issue is solved: at the mesoscopic scale,the Micro-CT Aided Geometrical Modeling(Micro-CT AGM)is developed.With the extraction of the real fiber tow morphological features,a mesoscopic material twin model of the textile is constructed.At the microscopic scale,a novel modeling approach is developed,which is to construct a microstructural model by directly inserting effective filaments to the mesostructural model of the textile.Meanwhile,a highly parameterized and automatic analyzing toolkit of numerical simulation is established.Distinguished from the traditional correlation approaches such as Digital Image Correlation(DIC),a novel correlation approach is developed to trace the movements of the contour points of fiber tows in the material twins under compaction,which calculates the relative radial displacements of the surface points to conduct the quantitive analysis of the deformation of textile at the mesoscopic scale.After that,the flow simulation is performed based on material twins,then with the experimental measurement,the saturated transverse permeability of the woven fibrous reinforcement is analyzed.Finally,in order to study the circular membrane instability,a reduced model is developed based on the method of Fourier series with slowly variable coefficients.This enriches the family of the reduced elements,which provides an effective and precise analyzing tool for the membrane wrinkling phenomena in LCM.With the research mentioned above,a platform for the analysis of meso-microscopic geometric modeling and numerical simulation of the woven fibrous reinforcement is established.Then the meso-microscopic analyzing tool of the permeability and the compressibility of the reinforcement is developed.This provides critical scientific supports for the analysis and optimization of certain procedures in LCM processes.