Influence Of Pre-deformation On The Permeability Of 2.5D Woven Preform

As an inherent attribute of woven materials,permeability describes the impediment of fibers to resin flow and is an important input parameter for analyzing RTM process.During the process of fabricating curved composites of 2.5D woven fabric,the loaded pre-deformation,which is required in process,will trigger a structural change of woven fabric and thereby make a difference on permeability.Based on the researching achievements in previous literature,this paper performed a detailed investigation into the influence of per-tension deformation and per-shear deformation on the permeability of preform.Our work may be helpful to optimize the RTM process and thereby improve quality of composite product.Since the prediction of the permeability of the preform is of great significance to simulate the RTM mold filling process,a serial of numerical analysis,cooperated with experiments,was conducted to predict the permeability of the 2.5D woven fabric preform.Based on microstructure of 2.5D woven fabric captured with OLMPUS microscope scanning,a representative unit cell with racetrack sectional yarns was employed to simulate the flowing process of resin within and between the yarns and consequently calculate the equivalent permeability of the whole cell model.To verify the simulation results,in-plane principal permeability of the fabric was measured experimentally in radial method and good agreement was obtained.According to the spatial configuration of bonded warp yarns,a theoretical model was developed to analyze deformation of prefabricated parts with help of numerical analysis.The deformed unit cell model was reconstructed and imported into the Fluent fluid simulation software.The corresponding permeability values were solved iteratively,and the relationship between tensile deformation and permeability values was obtained.A combination of finite element simulation and experimental testing was used to investigate the relationship between shear angle produced by shear predeformation and permeability.The deformed unit cell model was reconstructed after shear deformation and the in-plane permeability value was predicted by simulation.Perform was deformed at a certain shear angle by set-up of picture frame shearing and the in-plane permeability was measured using the radial method.Considering a good understanding of pressure field,velocity field and position of flow front in RTM process resin filling process is vital to prevention of defects,commercial software PAM-RTM was employed to simulate the in-plane permeability process of 2.5D woven fabric.By comparing with experiment results,applicability of the software was validated,based on which the mold design was optimized and filling process of tensile deformation fabric was simulated.