Research On Permeability And Properties Of High-thickness Carbon Fiber Composites

Vacuum Assisted Resin Transfer Molding is an ideal method to fabricate large size composite components at low cost,which has been widely used in aircraft,ship and wind turbine blade manufacturing.Permeability is an inherent property of fiber reinforced materials,which is used to describe the hindrance of fiber to resin flow,and is also an important parameter in the filling process of VARTM.In this paper,the preparation technology of ultra-long and high-thick CFRP was studied,the permeability of CFRP fabric in three directions was emphatically studied,and the mold filling process of CFRP girder with length of 90m,width of 800mm and thickness of 60mm of wind turbine blade was simulated by finite element method.The precision of permeability prediction of carbon fiber fabric determines the accuracy of finite element analysis in the filling process of VOTM.In this paper,the permeability of unidirectional carbon fiber fabric in three directions is predicted by numerical simulation method.Firstly,according to the structural characteristics of the fabric,five kinds of singleton were established based on the singleton method,namely,elliptical singleton,race-like singleton,race-like singleton,partially offset singleton,and maximally offset singleton.The permeability of the whole single cell model in X,Y and Z directions was obtained by simulation software.The results show that in a certain range,with the increase of fiber volume content,the gap between fiber bundles and fiber bundles becomes smaller,the high velocity area becomes smaller,the permeability of single cell also decreases gradually,and the pressure nephogram is evenly distributed gradually.Compared with the permeability in X,Y and Z directions,the permeability in the direction of fiber bundle is the largest,while the permeability in the direction of transverse and thickness is low.The migration between layers will also affect the permeability in X,Y and Z directions.The VARTM filling process of wind turbine blade carbon fiber girder is studied.According to the structural characteristics of the carbon fiber main girder of wind turbine blade,the main girder model is established.Five kinds of filling schemes were simulated by finite element software,and the pressure field and the position of the flow front in the mold cavity at any moment were obtained by simulation.The forming process and position of defects in the filling process were analyzed and the technological parameters were optimized.By the simulation result shows that the scheme 5 fabric layer at the bottom in the laying of guide network,suction pipe is set in the preforming on either side of the body surface along the length direction of the flow design,resin molding time is 5650 seconds,the mold filling time and gel time of the epoxy resin is match,with both sides extraction well reduce the formation of dry patches.Finally,the simulation results of Plan 5 were verified by experiments.The main girder was prepared by VARTM process,and the actual filling time was 1.7 hours,which was within the time range of epoxy resin gel.The full-scale nondestructive testing of the carbon fiber girder was carried out by the phased array ultrasonic testing equipment.The results show that the forming quality of the girder is good,and the content of defects such as dry spots and pores is within the allowable range of the production quality requirements of wind turbine blades.