Prediction of optimal flow front velocity to minimize void formation in dual scale fibrous reinforcements

Lebel, François; Fanaei, Amir Ershad; Ruiz, Édu; Trochu, F.

doi:10.1007/s12289-012-1111-x

Cited by 47 publications

(49 citation statements)

References 59 publications

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“…Following the approach adopted in previous work [18,32], it is hypothesized that the optimal velocity can be evaluated as the imbibition velocity for which an elementary cell is filled up with liquid during a capillary test. The characteristic size L c of the unit cell corresponds to the distance between two fiber bundles (see is Figure 9).…”

Section: Optimal Imbibition Velocitymentioning

confidence: 99%

“…However, such a procedure is highly time consuming and is only valid for a given resin/reinforcement system. To speed up the characterization stage, an alternative approach based on capillary imbibition was proposed by Lebel et al [18].…”

Section: Introductionmentioning

confidence: 99%

“…The paper is divided into two main sections. Following the approach proposed by Lebel et al [18], an improved experimental and data processing procedure is first presented, and the new methodology is applied to study the wicking behavior of a glass fabric reinforcement with a reference fluid. The results are then modeled to predict the optimal injection velocity range during mold filling with typical RTM thermosetting resins.…”

Section: Introductionmentioning

confidence: 99%

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Capillary Characterization of Fibrous Reinforcement and Optimization of Injection Strategy in Resin Transfer Molding

2018

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During composite manufacturing, minimizing the residual void content is a key issue to ensure optimal mechanical performance of final products. For injection processes such as Resin Transfer Molding (RTM), the impregnation velocity has a direct impact on void creation at the flow front by mechanical entrapment of air bubbles. Previous work proposed to study capillary imbibition in fibrous reinforcement to determine optimal filling conditions during practical manufacturing. The objective of this study is to investigate further this possibility. For that purpose, an improved experimental procedure is proposed to estimate the optimal impregnation velocity from capillary rise tests and understand its effect in parts of varying geometry. Capillary rise experiments were carried out with an enhanced experimental protocol, and a new post processing technique was evaluated to analyze the results. The position of the capillary flow front was then used to deduce the optimal impregnation velocity range based on the Lucas-Washburn flow model. A series of injections were also carried out with a laboratory scale RTM mold to study the influence of flow velocity on the residual void content. Results show that the prediction from capillary characterization is close to the optimal velocity value deduced from manufacturing experiments. The study also highlights the importance of void transport during processing and suggests that the injection strategy (i.e., flow rate history) and the mold configuration (i.e., divergent versus convergent flow) are important process parameters that may influence void content and cycle time.

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Section: Optimal Imbibition Velocitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Capillary Characterization of Fibrous Reinforcement and Optimization of Injection Strategy in Resin Transfer Molding

2018

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“…For instance, they can appear when the resin starts curing prematurely during impregnation, thus locally slowing down or partially blocking further resin flow. Dry spots can also originate from the well-documented race tracking phenomena, channeling effects due to high permeability areas, and converging flows when inlet ports are not placed properly (Lawrence et al, 2002;LeBel et al, 2014;Matsuzaki et al, 2014;Naik et al, 2014). Preform permeability with a constant fiber volume fraction is expected to be uniform throughout the mold before resin flow.…”

Section: Dry Spots Formation In Lcmmentioning

confidence: 99%

“…Nonetheless, the anisotropy and spatial variability of preform reinforcement are considered the major sources of race tracking, leading to dry spot formation (Lawrence et al, 2002;LeBel et al, 2014;Matsuzaki et al, 2014;Naik et al, 2014). Race tracking occurs when the resin flows along the edges of the mold ahead of the main impregnating flow.…”

Section: Dry Spots Formation In Lcmmentioning

confidence: 99%

Process Induced Defects in Liquid Molding Processes of Composites

Hamidi

Altan

2017

International Polymer Processing

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Liquid Composite Molding (LCM) processes are cost efficient manufacturing alternatives to traditional autoclave technology for producing near-net shape structural composite parts. However, process induced defects often limit wider usage of LCM in structural applications. Thorough knowledge of these defects, as well as their formation mechanisms and prevention techniques, is essential in developing improved LCM processes. In this article, process induced defects in liquid molding processes of composites, categorized into preform, flow induced and cure induced defects, are reviewed. Preform defects are further presented as fiber misalignment and fiber undulation (waviness and wrinkling). The respective causes, detrimental effects, and possible prevention methods of these defects are presented. Thereafter, flow induced defects are classified as voids and dry spots. Dry spot formation mechanisms in LCM processes and available prevention techniques are summarized. In addition, void formation mechanisms, adverse effects on composite properties, and removal techniques are presented. Cure induced defects include microcracks, void growth and geometrical distortions (warpage and spring-in). Each of these defects are discussed along with their underlying causes as well as their control and reduction schemes.

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Void content analysis and processing issues to minimize defects in liquid composite molding

2017

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This investigation aims to study the impact of key process parameters dealing with the resin impregnation of fibrous reinforcements used in Liquid Composite Molding (LCM). The process parameters are the flow front velocity, the inlet mold pressure and the bleeding flow rate. The experimental setup consists of a computer‐assisted injection system and a Resin Transfer Molding (RTM) mold that allows monitoring the progression of the flow front and study the effects of resin bleeding and applying post‐fill resin pressure during cure (also known as “mold packing”). Three sets of RTM injections were carried out with a vinyl ester resin and a bidirectional 0°/90° E‐glass noncrimp fabrics under (1) constant injection pressure, (2) constant injection flow rate, and (3) bleeding as well as mold packing after filling. The quality of injected parts was evaluated by standard void content analysis based on ASTM burn‐off (D2734) tests. The experimental results are consistent with published data and with predictions of the optimal impregnation velocity obtained from capillary rise tests. This study also shows that the impregnation of fibrous reinforcements in LCM can be improved through various injection strategies, namely monitoring of the flow front velocity and specific post‐filling procedures. POLYM. COMPOS., 40:109–120, 2019. © 2017 Society of Plastics Engineers

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Prediction of optimal flow front velocity to minimize void formation in dual scale fibrous reinforcements

Cited by 47 publications

References 59 publications

Capillary Characterization of Fibrous Reinforcement and Optimization of Injection Strategy in Resin Transfer Molding

Capillary Characterization of Fibrous Reinforcement and Optimization of Injection Strategy in Resin Transfer Molding

Process Induced Defects in Liquid Molding Processes of Composites

Void content analysis and processing issues to minimize defects in liquid composite molding

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