Numerical simulation of LCM mold-filling during the manufacture of natural fiber composites

Abstract

In this paper, a finite element/control volume (FE/CV) method based computer code is adapted to simulate the flow of resin-like liquids in swelling jute fabrics during the manufacture of natural-fiber composites using the liquid composite molding (LCM) technique. A novel treatment of the continuity equation using the rigorous volume-averaging method indicates that the despite liquid absorption and fiber swelling, the form of the continuity equation may remain identical to the traditional form seen for non-absorbing carbon or glass fibers. Such a continuity equation in conjunction with the Darcy's law with a time-varying permeability function is employed to model the resin flow as a fully saturated porous medium flow behind a clearly defined liquid front. Two new methods of estimating the time-varying local permeability and porosity of the wetted fiber mats behind the moving liquid-front are proposed. Later, the two time-dependent permeability models, one based on direct experimental estimation and the other based on indirect estimation using the Kozeny-Carman model, are used to alter permeability in finite elements behind the moving liquid-front during the numerical simulation. Such numerical modeling of the mold-filling process, as applied to the one-dimensional flows with constant flow rate and constant injection-pressure conditions, shows significant improvement over the traditional analytical solution obtained for a constant permeability. A good prediction of the experimentally observed flow-front location and inlet-pressure evolution plots by the two permeability models is observed. Of the two permeability models, the one based on direct estimation of permeability is found to be superior to the one employing the indirect approach. The novel analytical solution developed for the constant flow-rate (one-dimensional flow) case under a time-dependent permeability is shown to perform extremely well while predicting the flow-front location and inlet pressure evolution.

Modeling of resin flow in natural fiber reinforcement for liquid composite molding processes

“…Subsequently, the size of the flow path decreases and the flow characteristics may also be altered. It is well known that this fiber swell phenomenon leads to a change of reinforcement permeability during the mold filling process [5][6][7][8]. This mechanism is illustrated in Fig.…”

“…Masoodi et al performed the flow modeling in swelling porous medium such as natural fiber reinforcement considering a timedependent change of permeability because of the fiber swell [5,6]. In their work, the permeability was assumed to be uniform in the wet preform even though it was modeled as a timedependent variable.…”

“…In contrast, the increase of fiber diameter that pushes the resin outward can be regarded as a mass generation that increases the resin flow velocity. Masoodi et al proposed a new mass conservation equation by introducing mass sink and source terms representing these counteracting mass loss and generation effects [5,6]. In their work, it was however assumed that the fiber volume increase by the fiber swell was equal to the liquid volume absorbed into the fiber, and consequently, these mass loss and generation effects were cancelled out with each other [5,6].…”

Unsaturated and Saturated Permeabilities of Fiber Reinforcement: Critics and Suggestions

“…Some researchers corrected the unsaturated permeability considering the surface tension effect at the flow front (Ahn et al, 1991;Amico and Lekakou, 2001). On the contrary, some researchers argue that the influence on the capillary pressure is insignificant because the capillary pressure estimated from the characteristic pore size is much smaller than the inlet pressure (Masoodi et al, 2012).…”

Characterization and Processing of Nanocellulose Thermosetting Composites

“…Pillai et al were also the first to incorporate these equations into their finite element/control volume-based LCM mold-filling simulation [96]. The new mold-filling physics developed for swelling LCM preforms, when rigorously tested against experiments, was found to be superior to the conventional flow physics used for non-swelling preforms [112,113].…”