Theoretical Simulation Of Self-assembly And Functionalization Of Several Low-dimensional System

Liquid Composites Molding(LCM)technology is widely used in aerospace,new energy vehicle and other high technology industries recently.It is used to produce complex structure and high precision composite components by injecting resin into the dry fabric structure preform.The fabric structure preform is a kind of porous medium with complex and multi-scale structure characteristics.The fluid seepage law of LCM injection molding process is complex,and it is easy to form dry spots,pores and other defects,which seriously affect the quality and performance of composite materials.Aiming at the characteristics of multi-scale structure of fabric structure preform,it is an urgent problem in engineering to systematically study the law of liquid seepage in the injection process of LCM and optimize the process parameters of LCM.In this paper,the structural characteristic of fabric preforms are systematically studied from the perspective of multi-scale,the seepage model of fiber bundle,unidirectional fabric and 2.5D angle interlocking fabric is established,the liquid seepage law in fabric preforms at multiscale is studied,and the injection process parameters of LCM are optimized,which lays a theoretical and technical foundation for the high-quality manufacturing of high-performance composite materials.The main work of this paper includes:(1)Based on the principle of hard core algorithm,the molecular force interaction between fibers and the principle of minimum energy are introduced,and a hard core optimization algorithm is proposed to establish the fiber random distribution model of fiber bundle with the fiber filling factor up to 80%.On this basis,assuming that the fiber is an impermeable solid,a fiber bundle seepage model is established to analyze the effect of fiber filling factor and fiber distribution on the seepage performance of the fabric structure preform at the microscale,which can provide reasonable input information for the mechanical properties of the mesoscale fiber bundle within fabric structure preform.(2)Based on the virtual fiber model and the kinematic model,the fabric cell models of unidirectional fabric and 2.5D angle interlocking fabric are established.Assuming that tow is the permeable porous media,the Navier-Stokes/Brinkman equation is used to describe the liquid seepage behavior within tow,and the Navier-Stokes equation is used to describe the liquid seepage behavior between tows,and a dual-scale coupling seepage model of the fabric cell including the intra tow/inter tow is established.On this basis,the influences of surface compaction and structural parameters on the permeability of unidirectional fabric and 2.5D angle interlocking fabric are analyzed.Compared with the experimental results of fabric radial seepage,the correctness and rationality of the dual-scale seepage model of fabric cell are verified.(3)Aiming at the deformation of fabric in LCM process,on the basis of the undeformed 2.5D angle interlocking fabric cell model,the deformed 2.5D angle interlocking fabric cell model is obtained by applying shear boundary,and the dual-scale seepage model of the deformed 2.5D angle interlocking fabric is established.The effect of shear angle on the permeability of 2.5D angle interlocking fabric is analyzed.In addition,a variable Kozeny coefficient was introduced to establish a semi-empirical prediction formula for the permeability of deformed 2.5D angle interlocking fabrics with fiber volume fraction and shear angle.(4)The simulated annealing algorithm was introduced into the genetic optimization algorithm,combined with the geometric modeling of the fabric structure prefabricated body,the prediction of the permeability performance and the simulation of the mold filling process to establish the LCM mold filling optimization system of the fabric structure prefabricated body.The optimal design of multiple injection holes for flat and three-dimensional curved shells with the aim of filling time is realized.The feasibility and effectiveness of the mold filling optimization system are verified by comparing with the macroscopic mold filling experiment.The research method in this paper is also applicable to other types of fabric structure preforms,which provides a reliable theoretical basis and method for improving the preparation quality of fabric composites.