Percolation Characteristics Of Nanofiber Membrane Sandwich Resin Matrix Composites

Glass fiber reinforced polymer laminates are widely used due to their advantages of low cost,low density,high strength and design versatility.However,the failure mode of delamination caused by weak performance between layers strongly influences their fatigue life.In recent years,the interleaving of electrospun nanofibrous membranes into interlaminar zone has been one of the hotspots in the field of composite materials due to the fact that electrospun nanofibrous membranes can be used as secondary reinforcements to improve the mechanical properties of composites.But the interleaving of nanoscale fibrous membranes complicates the flow of liquid resin.In order to investigate the effect of interlaminar nanofibrous membranes on permeability property of glass fiber fabrics,in this paper,the PVAc/TiO₂ hybrid nanofibers were prepared by electrospinning and introduced into the interlayer of plain glass woven fabrics as primary reinforcements.The super depth of field optical microscope was employed to characterize the microstructure of glass fiber fabric with different nanofiber contents.The permeability of glass-fiber preforms incorporated with interlaminar nanofibrous membranes was measured by the radial flow experiments with emphasis on the effect of the nanofiber contents on the impregnating pattern of resin flowing in glass-fiber preforms.The results show that the millimeter-scale regions between glass fiber bundles are filled and discretized into micron-scale regions.Both the porosity and permeability values of preforms decrease with the nanofiber contents increasing.The anisotropy extent of preform was decreased as the increase of nanofiber contents.The area fraction of partially saturated regions behind resin macroscopic front increases with the nanofiber contents increasing.The area fraction of partially saturated region of preforms with the same nanofiber contents increases frstly,and then decreases with injection time increases.Based on the study of the permeability property of the glass-fiber preforms incorporated with interlaminar nanofibrous membranes,after the organic component of the PVAc/TiO2 hybrid nanofibrous membranes attached to the surface of the glass fiber fabric being removed by the high temperature sintering process,a new nanofibrous structure-cracked TiO2 nanofiber sheets were fabricated.The effects of the amount of spinning precursor solution,spinning voltage and sintering temperature on the morphology of the cracked TiO2 nanofiber sheet and its distribution on the surface of the glass fiber bundle were characterized by scanning electron microscopy（SEM）.The permeability of glass-fiber preforms incorporated with the interlaminar cracked TiO2 nanofiber sheet was measured by the radial flow experiments with emphasis on the effect of the cracked Ti02 nanofiber sheet on the impregnating pattern of glass-fiber preforms.The results show that the nanofiber sheets cracking along and perpendicular to the glass fiber direction were distributed only on the surface of the glass fiber bundle.However,unlike the PVAc/TiO2 fibrous membranes,the basic structure of the composite preforms incorporated with the cracked TiO2 nanofiber sheet were still orthotropic.And the change in thickness and porosity of the composite preform was negligible due to the smaller size of the cracked TiO2 nanofiber sheet.Due to the "cracked" porous structure,the two principal permeability values of the composite preform increased by two orders of magnitude compared to the blank glass-fiber preform.A certain positive or negative correlation exist between the microscopic and macroscopic flow due to the synergistic effect of synchronization,delaying action and local structural deformation.