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

Abstract

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.

Capillary Effects in Fiber Reinforced Polymer Composite Processing: A Review

“…The soil science version of the capillary number (Ca*), as written in Eq. 2, is preferred in some studies, introducing the static contact angle between the matrix and fibrous reinforcement (θ 0 ) (Ruiz et al, 2006;Ravey et al, 2014;LeBel et al, 2017).…”

“…Moreover, the signal is also significantly intensified. Lebel et al (LeBel et al, 2017;LeBel et al, 2019) employed VLT to characterize the relation between processing conditions, i.e., Ca*, and saturation of a glass fabric. The increased light intensity allowed them to accurately estimate the local void content after calibration with burn-off composites after consolidation.…”

“…Partially saturated regions indeed show a broad distribution of pore channel diameters and thereby capillary forces act at a wide range of scales, therefore in macroscopic studies, the capillary pressure is represented by an average of multiple capillary pressure jumps inside a small region (RVE). Moreover, the progressive saturation is directly linked to a progressive filling of the pores and can be in turn related to void mechanisms during the infiltration (Park and Lee, 2011;LeBel et al, 2017). Two main strategies are commonly adopted to tackle unsaturated flow phenomena: two-phase flow and dualscale approaches (Michaud, 2016).…”

Optical measurement of voids in situ during infusion of carbon reinforcements

“…These methods involve electrical conductivity, 22,31 thermal conductivity, 32,33 ultrasound, 34–36 magnetic resonance imaging, 37 flow-rate comparison, 38,39 and overall light transmission. 40,41 All but the latter could be theoretically performed on carbon reinforcements, although only one of the above studies presented quantitative measurements for carbon. 32 A weakness of such methods is that no information on individual bubbles is available, e.g.…”