Liangchao Fang

Effect of Nesting on the Out-of-Plane Permeability of Unidirectional Fabrics in Resin Transfer Molding

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.

Non-uniform capillary model for unidirectional fiber bundles considering pore size distribution

Capillary rise affects void inclusion during the impregnation of fiber reinforcements in resin transfer molding. A new model of effective capillary radius has been developed to investigate the effect of pore size distribution on capillary flow in unidirectional fiber bundles. With the image analysis method, the statistical results showed that the pore size distribution could be very different even for the same fiber volume fraction. Then, the classical Washburn equation, in conjunction with different models for calculating effective capillary radius, was applied to predict the capillary rise rate. Compared with the experimental results, we found that the new model performed better than traditional models where the effective capillary radius was obtained using average pore radius or hydraulic radius.

Effect of layer shift on the out-of-plane permeability of 0°/90° noncrimp fabrics

Layer shift has a great effect on the permeability which is a key parameter in resin transfer molding. In this paper, nine different unit cells were modeled based on the range of layer shift and decomposed into zones of characteristic yarn arrangement, respectively. For each unit cell, a set of equations was derived allowing description of the local permeability of each zone as a function of geometrical yarn parameters. The overall permeability was then modeled as a mixture of permeabilities of different zones with the electrical resistance analogy. Excellent agreement was found between predictions and experiment. Both results indicated that the channel flow had a dominant role in the whole flow through the fabrics. And the permeability values reached maximum when the empty regions were interconnected between upper and lower layers. In addition, the effect of fiber volume fraction on the differences of two extreme cases was also investigated.

Effect of Nesting on the Permeability of Multilayer Unidirectional Fabrics

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.