Progress in Experimental and Theoretical Evaluation Methods for Textile Permeability

Abstract

A great amount of attention has been given to the evaluation of the permeability tensor and several methods have been implemented for this purpose: experimental methods, as well as numerical and analytical methods. Numerical simulation tools are being seriously developed to cover the evaluation of permeability. However, the results are still far from matching reality. On the other hand, many problems still intervene in the experimental measurement of permeability, since it depends on several parameters including personal performance, preparation of specimens, equipment accuracy, and measurement techniques. Errors encountered in these parameters may explain why inconsistent measurements are obtained which result in unreliable experimental evaluation of permeability. However, good progress was done in the second international Benchmark, wherein a method to measure the in-plane permeability was agreed on by 12 institutes and universities. Critical researchers’ work was done in the field of analytical methods, and thus different empirical and analytical models have emerged, but most of those models need to be improved. Some of which are based on Cozeny-Karman equation. Others depend on numerical simulation or experiment to predict the macroscopic permeability. Also, the modeling of permeability of unidirectional fiber beds have taken the greater load of concern, whereas that of fiber bundle permeability prediction remain limited. This paper presents a review on available methods for evaluating unidirectional fiber bundles and engineering fabric permeability. The progress of each method is shown in order to clear things up.

Numerical and experimental investigation of saturated transverse permeability of 2D woven glass fabrics based on material twins

“…Since the simulations are conducted in representative regions extracted from the material twins created with 10 fabric layers, five combinations of layers for NOL = 6 and three for NOL = 8 have been studied, so that error bars can be provided for simulation results along the x and y axes. Thus, numerical predictions can also illustrate the variability of the material much like experiments, which was generally not possible in previous studies . Meanwhile, differently from other investigations that assume a uniform distribution of fiber volume content in one fabric stack, the geometric models used in numerical simulation are constructed from real fabrics so that the nesting and distortion between fabric layers can be precisely described without any particular assumption.…”

“…Thus, numerical predictions can also illustrate the variability of the material much like experiments, which was generally not possible in previous studies. [19,[35][36][37][38][39] Meanwhile, differently from other investigations that assume a uniform distribution of fiber volume content in one fabric stack, the geometric models used in numerical simulation are constructed from real fabrics so that the nesting and distortion between fabric layers can be precisely described without any particular assumption. As illustrated in Figure 14, these phenomena can cause significant variations in fiber volume content and predicted permeability, which explain the overall variability of simulation results.…”

“…Hence, the liquid can flow only through the mesopores between fiber tows. These microscopic effects can usually be neglected in the evaluation of saturated permeability, although this might not be the case for the unsaturated permeability as the micropores are progressively filled up during mold filling. Thus, the mesoscopic and microscopic scale flows can be decoupled, although it might lead to an underestimation of the predicted permeability.…”

“…Compared to experiments, numerical simulation is an efficient way to study the permeability of engineering fabrics to reveal the critical phenomena occurring during the impregnation in LCM processes both at the mesoscale and microscale levels. [19,[35][36][37][38][39] However, the comparison between numerical predictions of transverse permeability and experiments still remains a challenge because the mesostructural models are generally constructed by idealized modeling approaches. Thus, most simulation results cannot take into account the effect of material variability as in experiments.…”

Out-Of-Plane Permeability Evaluation of Carbon Fiber Preforms by Ultrasonic Wave Propagation

“…A suitable process design is necessary, which requires knowledge about different parameters affecting the filling behavior, such as mold geometry, resin viscosity, number and position of inlet and vent ports, etc. [18]. Besides the previous parameters, one of the most critical is the permeability of the reinforcement, defined as the resistance exhibited by the fibrous reinforcement against the resin flow [19].…”