Mechanism of Void Formation in Composite Processing with Woven Fabrics

Abstract

A mechanism for void formation is suggested, involving an analysis of the resin flow at macro and micro levels. Both these types of flow arise from the characteristic structure of woven fabrics. In order to investigate the mechanism of void formation in woven fabrics, a new dimensionless number was defined as the ratio of the superficial velocity to the initial spreading rate. The prediction of void formation using this dimensionless number had a good correlation with the results from the cross sectional observation and void content measurement. It was confirmed that the mechanism introduced in this study is very desirable and that the morphological structure of the woven fabric plays a key role in void formation.

Optimization of injection flow rate to minimize micro/macro-voids formation in resin transfer molded composites

“…In early investigations, the formation of microscopic and macro-scopic voids has been related to the capillary number (Ca) [5][6][7][10][11][12]. Patel and Lee [5] proposed a modified capillary number (Ca*) that considers the liquid/fiber contact angle and the liquid surface tension…”

“…In the past, researchers have published several investigations on micro-and macro-void formation [4][5][6][7]. Experimental as well as numerical analyses were also performed to identify and describe the mechanisms of void formation [8,9].…”

“…Considering Ca à opt as a fixed parameter that can be experimentally measured [4][5][6] or numerically estimated …”

Modeling and simulation of filling in dual-scale fibrous reinforcements: state of the art and new methodology to quantify the sink effect

“…This difference can lead to formation of voids by mechanical entrapment of air; voids formed inside the tows are named microvoids and voids formed in the channels are known as macrovoids. In general, a high velocity of the injected liquid with respect to the capillary velocity inside the tows leads to the formation of microvoids and a low velocity, to formation of macrovoids, 14 as is illustrated in Figure 7. The complexity of the simulations in dual-scale fibrous reinforcements lies in the consideration of two domains with different scales of permeability.…”

“…Some works using these strategies can be found elsewhere. 9–16 In the present work, the second strategy is implemented.

Figure 2.Type of filling problems in dual-scale fibrous reinforcements.

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