Nesting of layers is the main source of the variations in permeability values in liquid composite molding (LCM) processes. In this paper, the permeability of unidirectional fabrics was modeled as a function of layer shift and geometrical yarn parameters to study the effect of nesting. Firstly, three different unit cells of two layers were modeled based on the range of layer shift and decomposed into zones of characteristic yarn arrangement, respectively. The overall permeability of each unit cell was then modeled as a mixture of local permeabilities of different zones with the electrical resistance analogy. Secondly, every two adjacent layers were regarded as porous media with different permeabilities. The permeability of multilayer unidirectional fabrics was then modeled with electrical resistance analogy. As the unpredictability of layer shifting in actual process, the statistical characteristics were analyzed theoretically and validated with experimental measurements. Excellent agreement was found between predictions and experiment data.

The research of green chemical recycling of thermosetting carbon fiber composites has been widely concerned by scholars. In this paper, the recycling of high-performance carbon fiber epoxy/resin composites(CF/EP) were conducted in a shorter time and at much lower temperature than those reported recycling methods. The CF/EP were pretreated in nitric acid to be initially decomposed and layered, then the layered CF/EP were subjected to macrogol 400 in presence of potassium hydroxide at 160 °C for 200min. As a result, the carbon fiber was separated and recovered from epoxy resin. Specifically, resin removal rate was more than 95 wt%, and the tests of X-ray photoelectron spectra and scanning electron microscope revealed that surface of recovered fiber was close to that of virgin fiber. In addition, dynamic contact angle meter shown that surface wettability of recovered fiber was improved, which might contribute to the infiltration of resin. On the other hand, the mechanical properties of recovered carbon fiber decreased slightly compared with those of virgin fiber. As mentioned above, the recycling of CF/EP was realized under mild conditions and the performance of recovered carbon fiber was well preserved. This means that the efficient method to recover CF/EP showed great commercial application potential.

•The contact angle in capillary is generally greater than 0° and multivalued.•The model of solid-liquid static contact angle considers the meniscus surface of liquid.•The paper constructs incomplete wettability system contact angle model that could accurately predict the contact angle.•The prediction error of the contact angle is less than 3% by using the prediction model of the paper.•Experimental conclusions will play an important guiding role in research field of contact angle.The solid-liquid contact angle which reflects the wettability of solid-liquid system is determined by the physical nature of solid-liquid medium and environmental factors. Through experiments we discovered that the value of contact angle in capillary is generally greater than 0° and multivalued. In addition, the experiments show that as the tube diameter increases, the equivalent height of liquid meniscus increases; as the liquid column height increases, the equivalent height of liquid meniscus decreases. In order to build the solid-liquid static contact angle model of incomplete wetting system, we established the equivalent height function with the capillary diameter as the independent variable. Furthermore, the contact angle model was constructed based on the Jurin formula. The experiments indicated that the model was coincident with the experimental data, what is more, the forecast errors of the contact angle were less than 3%. The model had higher prediction precision compared with that of Jurin or Rayleigh formula. Meanwhile, the reasonability of the modeling method and the practicability of the model are also verified by the paper.

•Graphene oxide coated carbon fiber was prepared by EPD.•SEM results indicate that fiber surfaces were deposited with GO.•Ultrasonic is beneficial to EPD of GO on carbon fiber surface.•GO enhanced the surface activity and wettability of carbon fibers.•GO has contributed to the interfacial properties of composite.Graphene oxide coatings were utilized to enhance the interfacial properties of carbon fibers. In this work, a facile route is proposed to prepare graphene oxide/carbon fiber hybrid fiber via ultrasonically assisted electrophoretic deposition (EPD) without complex chemical reactions and long processing time. Surface functional group, surface roughness and surface morphologies of carbon fibers were examined by Fourier transform infrared spectrometer (FTIR), atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. Surface free energy of the fiber was characterized by dynamic contact angle analysis (DCAA). The results indicated that the deposition of graphene oxide introduced some polar groups to carbon fiber surfaces and changed the surface morphologies of carbon fibers. Surface wettability of carbon fibers may be significantly improved by increasing surface free energy of the fibers due to the deposition of graphene oxide. Comparing the results with EPD-only, ultrasonically assisted EPD increased the thickness and uniformity of graphene oxide coatings whereas only sparse deposition formed without ultrasonic. Short beam shear test was performed to examine the impact of carbon fiber functionalization on the mechanical properties of the carbon fiber/epoxy resin composites. An improvement of 55% from 36.7 to 56.9 MPa in interlaminar shear strength confirms the remarkable improvement in the interfacial adhesion strength of the composites.Graphene oxide coated carbon fiber was prepared by ultrasonically assisted electrophoretic deposition

The nesting of layers has great effect on the permeability which is a key parameter in resin transfer molding (RTM). In this paper, two mathematical models were developed to predict the out-of-plane permeability of unidirectional fabrics with minimum and maximum nesting, respectively. For different zones of characteristic yarn arrangement in the unit cell, the local permeability was modeled as a function of geometrical yarn parameters. The global permeability was then modeled as a mixture of permeabilities of different zones with the electrical resistance analogy. The influences of local permeability of each zone on the global value of unit cell were deeply researched. In addition, two different fabrics were tested and a reasonably good agreement was found between the model predictions and experimental results. We also found that the permeability values were two orders of magnitude larger with minimum nesting than with maximum nesting. However, the differences between minimum nesting and maximum nesting decreased with increasing fiber volume fraction.