Experimental study of saturation by visible light transmission in dual-scale fibrous reinforcements during composite manufacturing

2017 ◽  
Vol 36 (23) ◽  
pp. 1693-1711 ◽  
Author(s):  
F LeBel ◽  
É Ruiz ◽  
F Trochu
Keyword(s):  
Visible Light ◽  
Light Transmission ◽  
Void Formation ◽  
In Situ Monitoring ◽  
Injection System ◽  
Computer Assisted ◽  
Liquid Composite Molding ◽  
Composite Molding ◽  
The Impact ◽  
Dual Scale

A new in situ monitoring strategy is proposed to study void formation during real-time impregnation of dual-scale fibrous reinforcements in liquid composite molding. Void content data from burn-off tests are used to calibrate a refractive index matching approach based on two optical principles: Beer–Lambert and Fresnel laws. Once calibrated, this approach based on visible light transmission is used to study the impact of key process parameters on the saturation footprint of dual-scale fibrous reinforcements during and after mold filling. The injection parameters investigated are the flow front velocity, the pressure distribution inside the mold cavity, the bleeding flow rate, and the mold packing pressure. The experimental setup is a computer-assisted injection system and a transparent resin transfer molding mold is used to perform unidirectional injections. A vinyl ester resin is injected through E-glass bidirectional non-crimp fabrics under various manufacturing conditions. This investigation not only confirms the decreasing trend in void formation by mechanical entrapment of air with the decrease in impregnation velocity, as it converges toward the optimal impregnation conditions for this fibrous reinforcement reported in previous studies, but it also brings insights on void dissolution and transport in liquid composite molding.

Effect of Fiber Content on Void Morphology in Resin Transfer Molded E-Glass/Epoxy Composites

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Youssef K. Hamidi ◽  
Sudha Dharmavaram ◽  
Levent Aktas ◽  
M. Cengiz Altan
Keyword(s):  
Fiber Volume Fraction ◽  
Volume Fraction ◽  
Void Formation ◽  
Areal Density ◽  
Fiber Content ◽  
Epoxy Composites ◽  
Formation Mechanisms ◽  
Liquid Composite Molding ◽  
Fiber Volume ◽  
Composite Molding

Effect of fiber volume fraction on occurrence, morphology, and spatial distribution of microvoids in resin transfer molded E-glass/epoxy composites is investigated. Three disk-shaped center-gated composite parts containing 8, 12, and 16 layers of randomly-oriented, E-glass fiber perform are molded, yielding 13.5%, 20.5%, and 27.5% fiber volume fractions. Voids are evaluated by microscopic image analysis of the samples obtained along the radius of these disk-shaped composites. The number of voids is found to decrease moderately with increasing fiber content. Void areal density decreased from 10.5 voids/mm2 to 9.5 voids/mm2 as fiber content is increased from 13.5% to 27.5%. Similarly, void volume fraction decreased from 3.1% to 2.5%. Increasing fiber volume fraction from 13.5% to 27.5% is found to lower the contribution of irregularly-shaped voids from 40% of total voids down to 22.4%. Along the radial direction, combined effects of void formation by mechanical entrapment and void mobility are shown to yield a spatially complex void distribution. However, increasing fiber content is observed to affect the void formation mechanisms as more voids are able to move toward the exit vents during molding. These findings are believed to be applicable not only to resin transfer molding but generally to liquid composite molding processes.

Modeling void formation and unsaturated flow in liquid composite molding processes: a survey and review

2011 ◽  
Vol 30 (11) ◽  
pp. 957-977 ◽  
Author(s):  
Chung Hae Park ◽  
Lee Woo
Keyword(s):  
Unsaturated Flow ◽  
State Of The Art ◽  
Void Formation ◽  
Pressure Profile ◽  
Liquid Composite Molding ◽  
Simulation Studies ◽  
Apparent Permeability ◽  
Composite Molding ◽  
Unsaturated Flows ◽  
Key Parameter

In this study, we present a review of the modeling of void formation and unsaturated flow in liquid composite molding processes. We examine modeling efforts considering all the mechanisms involved such as void formation and transport, bubble compression, and gas dissolution. In particular, the capillary number is identified as a key parameter for void formation and transport. Numerical simulation studies are reviewed, and a state-of-the-art is presented. The influence of microvoids on the global resin flow is also investigated. To model the unsaturated flow more accurately, we suggest considering the surface tension or capillary pressure, variation in permeability in terms of saturation and fiber displacement, as well as tow saturation. From this investigation, the apparent permeability and pressure profile in saturated and unsaturated flows are compared.

A Model for the Two-Phase Flow Through a Dual-Scale Porous Medium in Liquid Composite Molding

2007 ◽  
Author(s):  
N. K. Yamaleev ◽  
R. V. Mohan
Keyword(s):  
Porous Medium ◽  
Two Phase Flow ◽  
Fiber Bundles ◽  
Phase Flow ◽  
Liquid Composite Molding ◽  
Two Phase ◽  
Individual Fiber ◽  
Composite Molding ◽  
Flow Through ◽  
Dual Scale

The macroscopic flow during processing of composite structures by liquid composite molding is accompanied by the microscopic flow through individual fiber bundles. This concurrent microscopic flow occurs at length and time scales different than those of the macroscopic flow and influences the macroscopic flow behavior, impacting the void formation during composite manufacturing. A reduced-order model developed by the authors of this paper in [Proc. 2005 ASME Conf., IMECE2005-82436] for modeling the microscopic impregnation of individual fiber bundles is currently used to simulate the transient dynamics of the 1-D two-phase flow though a dual-scale porous medium during resin transfer molding (RTM). As has been show in our previous work [Inter. J. of Multiphase Flow, Vol. 32, pp. 1219–1233, 2006] the vapor-liquid phase transition and multidimensional effects of the gas entrapped inside fiber tows can play a significant role in the advancement of the macroscopic resin front and the formation of voids, thus indicating the need to account for these phenomena in the simulation of liquid composite molding processes. These effects are quantified by introducing a nonzero sink term into the right hand side of the mass conservation equation for the dual-scale porous medium, which couples the microscopic two-phase flow inside fiber bundles with the macro-flow through the perform. Two numerical methods, one of which is based on the moving coordinate system associated with the macroscopic resin front and the other one based on the fill factor technique on a fixed Eulerian coordinate system, are used to solve the resin flow through the preform. The comparative analysis of the fill factor and moving front methods as well as the results demonstrating the effect of phase transition and impregnation of individual fiber bundles on macroscopic flow parameters during RTM are presented.

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