This work shows evidence of conventional liquid and polymer molecules doping macroscopic yarns made up of carbon nanotubes (CNT), an effect that is exploited to monitor polymer flow and thermoset curing during fabrication of a structural composite by vacuum infusion. The sensing mechanism is based on adsorption of liquid/polymer molecules after infiltration into the porous fibers. These molecules act as dopants that produce large changes in longitudinal fiber resistance, closely related to the low density of carriers near the Fermi level of bulk samples of CNT fibers, reminiscent of their low‐dimensional constituents. A 25% decrease in fiber resistance upon exposure to electron–donor radicals formed during epoxy vinyl ester polymerization is shown as an example. At later stages of curing the matrix undergoes shrinkage and applies a compressive stress to the fibers. The resulting sharp increase in electrical resistance provides a mechanism for detection of the matrix gel point. The kinetics of resistance change during polymer ingress are related to established models for macromolecular adsorption, thus also enabling prediction of polymer flow. This is demonstrated for vacuum infusion of a 150 cm2 glass fiber laminate composite, with the CNT fiber yarns giving accurate prediction of macroscopic resin flow according to Darcy's law.
In situ vacuum-assisted infiltration experiments were carried out using synchrotron X-ray computed tomography (SXCT) to study the mechanisms of microfluid flow within a fiber tow. A single tow of E glass fibers was infused with a water and syrup blend using an apparatus designed and built for this purpose. The high resolution of the SXCT images allows the detailed reconstruction of individual fibers within the tow while the contrast between the different phases (air, fluid and fibers) was enough to track the fluid front position and shape as well as the void transport during infiltration. The ability of this technique to provide detailed information of microfluid flow and void transport in composite materials is clearly established. The fluid propagation at the microscopic level as well as the mechanisms of void transport within the tow were related to the wetting between the fluid and the fibers, the rheological properties of the fluid and the local microstructural details (fiber
a b s t r a c tFluid flow and fabric compaction during vacuum assisted resin infusion (VARI) of composite materials was simulated using a level set-based approach. Fluid infusion through the fiber preform was modeled using Darcy's equations for the fluid flow through a porous media. The stress partition between the fluid and the fiber bed was included by means of Terzaghi's effective stress theory. Tracking the fluid front during infusion was introduced by means of the level set method. The resulting partial differential equations for the fluid infusion and the evolution of flow front were discretized and solved approximately using the finite differences method with a uniform grid discretization of the spatial domain. The model results were validated against uniaxial VARI experiments through an [0] 8 E-glass plain woven preform. The physical parameters of the model were also independently measured. The model results (in terms of the fabric thickness, pressure and fluid front evolution during filling) were in good agreement with the numerical simulations, showing the potential of the level set method to simulate resin infusion.
Two mathematical models are used to simulate pollution in the Bay ofSantander. The first is the hydrodynamic model that provides the velocity field and height of the water. The second gives the pollutant concentration field as a resultant. Both models a re formulated in two-dimensional equations. Linear triangular finite elements are used in the Galerkin procedure for spatial discretization. A finite difference scheme is used for the time integration. At each time step the calculated results of the first model are input to the second model as field data. The efficiency and accuracy of the models are tested by their application to a simple illustrative example. Finally a case study in simulation of pollution evolution in the Bay of Santander is presented.
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