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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 v...
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... there is a difficulty in terms of model- ing, because these two phenomena take place at differ- ent scales. Void formation should be considered at the fiber tow level (heterogeneous medium), while the global resin flow can be treated with an averaged approach using Darcy's law where a preform is regarded as a homogeneous medium ( Figure 3). Furthermore, these two phenomena are strongly cou- pled and interact with each other: the global resin pres- sure field affects the tow saturation and vice versa. ...
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... A single-gate, constant volume injection strategy is adopted, with an injection time of 60 s. As demonstrated in [26], or by analysing the Darcy's Law for fluid permeation through porous mediums [40][41][42], it is ...
... A single-gate, constant volume injection strategy is adopted, with an injection time of 60 s. As demonstrated in [26], or by analysing the Darcy's Law for fluid permeation through porous mediums [40][41][42], it is known that resin injection at different regions of the mould will require different amounts of injection pressure. Thus, the constant volume injection strategy was adopted in this study to ensure a complete mould filling across all different injection scenarios. ...
The Resin Transfer Moulding process receives great attention from both academia and industry, owing to its superior manufacturing rate and product quality. Particularly, the progression of its mould filling stage is crucial to ensure a complete reinforcement saturation. Contemporary process simulation methods focus primarily on physics-based approaches to model the complex resin permeation phenomenon, which are computationally expensive to solve. Thus, the application of machine learning and data-driven modelling approaches is of great interest to minimise the cost of process simulation. In this study, a comprehensive dataset consisting of mould filling patterns of the Resin Transfer Moulding process at different injection locations for a composite dashboard panel case study is presented. The problem description and significance of the dataset are outlined. The distribution of this comprehensive dataset aims to lower the barriers to entry for researching machine learning approaches in composite moulding applications, while concurrently providing a standardised baseline for evaluating newly developed algorithms and models in future research works.
... Fig. 11 presents an illustration of a dry-spot region. Another example can be found in Figure 1 of [74] wherein the dry-spot was identified in a composite sample that was prepared using the Liquid Composite Molding process [74]. This type of defect can occur due to various reasons such as premature gelling, air trapping during the merging of multiple resin flow fronts, or irregular permeability of the preform. ...
... Fig. 11 presents an illustration of a dry-spot region. Another example can be found in Figure 1 of [74] wherein the dry-spot was identified in a composite sample that was prepared using the Liquid Composite Molding process [74]. This type of defect can occur due to various reasons such as premature gelling, air trapping during the merging of multiple resin flow fronts, or irregular permeability of the preform. ...
... Porosity is another commonly occurring defect that refers to the presence of air or voids within the composite material [7,76]. It occurs due to entrapped air bubbles or inadequate resin flow during the manufacturing process [74]. Fig. 13 demonstrates an example of voids in composite material. ...
In recent decades, various pipeline industries, such as oil, gas, and water, have increasingly focused on fiber-reinforced polymer (FRP) pipes. This growing interest in FRP pipes offers multiple advantages over traditional pipelines made of steel and concrete, including exceptional corrosion resistance, a favorable weight-to-strength ratio, reduced maintenance costs due to its durability, and customer-specific customization in sizes and strength. However, the intricate manufacturing processes and its specialized handling and installation requirements make it susceptible to defects. The traditional non-destructive testing (NDT) methods, primarily developed for metals, are inadequate when applied to FRP. It is mainly because fiberglass composites are inherently non-homogeneous and anisotropic in contrast to their metallic counterparts, introducing a unique set of challenges. As a result, the fields of Non-destructive Testing & Evaluation (NDT&E) and Structural Health Monitoring (SHM) for FRP piping systems are currently vibrant areas of research and development. The objectives of this paper are (i) to identify potential damage types in composite pipelines, (ii) to compile a comprehensive list of defects currently examined in the literature, and (iii) to present the latest progress in NDT&E techniques for composite pipelines, specifically addressing the operational constraints and practical challenges involved. Consequently, it is tailored specifically to address the needs and challenges of the pipeline sector. It is found that the state of NDT for composite pipelines is still nascent, with extensive research required to reach maturity. Critical areas for development include broadening inspection ranges, validating performance in real-field conditions, detecting, and characterizing natural defects, and improving imaging techniques. Moreover, there is a need to transition from reactive to proactive strategies in pipeline monitoring.
... The void development during curing, which asserted that thermal expansion and diffusion could cause void sizes to fluctuate. Moisture-based voids' dissolution and development during resin curing [34] At low curing pressure, a sizable no of big blows created in the single layer interfaces, and as the pressure was raised, the size and number of these voids considerably decreased [35] Formation of void defects in RTM Due to the uneven resin flow during this procedure, air stuck with blows produced near the flow front [36] Multiple causes, including uneven dry-out can result in void defects in RTM [37] Mesoscopic voids will form between fibre bundles if the discharge rate of matrix is less than that of fibre bunches [38] On the other hand, micro-voids form b/w each segment in the bunch of fibres [39] The resin flow velocity and pressure will also be impacted by the creation of voids in composites [29] Formation of void defects in 3D printing ...
Composites made of fiber-reinforced resin are being used more and more in the aerospace and auto industries. However, owing to the complex physical and chemical characteristics of the constituent materials moulding techniques, making composites presents highly difficult hurdles. As a result, while assessing the quality of composites, knowledge on how to spot production-related issues is crucial. The matrix of composites’ residual stress development, Vacuum flaws and resin-rich flaws are first summarised. This chapter describes many resin-related processes, such as the curing of heat responsive resins. Resin penetration during hot pressing, RTM and 3D printing, and resin-rich flaws during the moulding process. Second, the method by which fibre reinforcement flaws such fibre waviness and wrinkle occur in composites is introduced, and the impact of such flaws on the creation of the composite structure is underlined. Supporting structure modulus, strength, and stability may be significantly reduced by fibre misalignment defects, according to several research reports. Finally, difficulties brought on by interfacial defects, like layer peel ups and unbinding are elaborated at the interface between reinforcements and matrix. By combining the different difficult aspects that cause manufacturing flaws in laminated and additively made structures so that the inculcated information may provide a prognosis for composite manufacturing.
... Phase separation has also been used to prepare a porous epoxy monolith 67 . Void formation and transport were also observed in liquid composite molding processes 68 . Thus, the Cahn-Hilliard equation may help to understand the formation mechanism of pores/voids in the manufacturing or service of FRP composites. ...
Fiber-reinforced polymer (FRP) composites have gained widespread applications in many engineering fields, making it imperative to study long-term performance under service conditions. Due to their heterogeneity and multifield coupling conditions, the long-term performance of FRP composites has become a complex scientific problem that involves multiscale and multidisciplinary aspects. With advancements in nanotechnology and computational power, researchers have increasingly conducted studies on the deterioration mechanisms and durability of FRP composites using top-down experiments and bottom-up multiscale simulations. Here, we review micro- and nano-mechanics in relation to the durability of FRP composites, including progress in the use of atomic and molecular simulations. We elucidate the role of multiscale methods, particularly molecular dynamics simulations, in the study of FRP composites and outline its prospects, to illustrate how micro- and nano-mechanics contribute to research on the durability of FRP composites.
... Few researchers have tried with different resin systems and special fibers for these studies [12,[27][28][29]. As we know that composite structures are manufactured by various techniques like pressure bag moulding, out of autoclave process, autoclave moulding [27], Resin Transfer Molding (RTM) [30][31][32][33][34] and vacuum bag moulding. These are prone to develop porosity in spite of efforts made to bring down the porosity level. ...
The effect of porosity has been studied by developing different levels of porosity laminates through a new autoclave based manufacturing technique known as Diverse Cure System (DCS). Further assessment of porosity levels by mechanical characterization (Inter-laminar Shear Strength), microscopic studies and acid digestion method have been achieved in Carbon Fiber Epoxy laminates. Correlations are obtained on the different levels for porosity laminates of two different thicknesses. ILSS test results are compared with the literature results. Assessment of porosity effect on ILSS is performed at room temperature and environmentally conditioned specimens. Strength degradation of 20 to 30% has been noticed on porosity laminates. Hygro-thermal specimens are tested at room temperature, elevated temperature and hot wet condition. A large reduction in the range of 45 to 53% in ILSS has been noticed on the moisture conditioned specimens tested at elevated temperature of 150°C.
... This manual operation may lead to undesired preforming defects, such as empty spaces or open channels between the mold wall and the fiber preform. As a result, during the impregnation stage, race tracking is likely to take place, leading to dry spots in the final manufactured part [9]. Although it might be possible to reduce these defects by improving tolerances of the preform cutting and layup and relying on the experience of the operators, it is not possible in general to know in advance whether flow channels will be created in the mold or not and how they will be distributed. ...
A numerical analysis of the influence of race tracking on dry spots formation and the accuracy of permeability measurement during the resin-transfer-molding process is presented. In the numerical simulation of the mold-filling process, defects are randomly generated, and their effect is assessed by a Monte Carlo simulation method. The effect of race tracking on the unsaturated permeability measurement and dry spots formation is investigated on flat plates. It is observed that the race-tracking defects located near the injection gate increase up to 40% of the value of the measured unsaturated permeability. The race-tracking defects located near the air vents are more likely to generate dry spots, whereas those near the injection gates have a less significant influence on dry spots generation. Depending on vent location, it has for instance been shown that the dry spot area can increase by a factor of 30. Dry spots may be mitigated by placing an air vent at a suitable location based on the numerical analysis results. Moreover, those results may be helpful to determine optimal sensor locations for the on-line control of mold-filling processes. Finally, the approach is successfully applied to a complex geometry.
... As the first and vital step during the PIP process, the efficiency of precursor infiltration largely determines the final density of the final composite. Efficient precursor infiltration should allow the precursor solution (polycarbosilane in xylene) to penetrate into both the large gaps between the tows (inter-bundle macro-pores) and the small voids within the tows (intra-bundle micro-pores) [25]. Here the infiltration process is considered as laminar flow of a Newtonian fluid through pipe channels, as idealised in Fig. S1 in Supplementary materials. ...
... However, this trend is not necessarily clear in practice. Indeed, identifying precisely the flow front can be difficult (Park and Woo 2011;Causse et al. 2018). Attribution errors such as depicted in Fig. 11 may lead to alter the observed distribution. ...
... This entails an overall regular advancement of the flow front and thus a lower final void content. Moreover, further mechanisms such as air compressibility and dissolution (Park and Woo 2011) tend also to diminish the residual proportion of vapour phase. ...
Transient two-phase flows within fibrous media are considered at local scale. Upscaling these flows constitute a key procedure towards a tractable description in an industrial context. However, the task remains challenging as a time-dependent behaviour is observed within a geometrically complex structure with interplay of various physical phenomena (capillary effects, viscous dissipation, etc.). The usual upscaling strategies encountered in both soil sciences and composite materials communities are reviewed, compared, and finally adapted to reach a method that is relevant to describe fibrous media imbibition. Using finite element flow simulations on statistical representative volume elements, the proposed approach first considers several definitions for saturation in order to characterise the flow dynamics as well as the characteristic length associated with the transient behaviour. Next, two methods are proposed to assess a resulting capillary pressure, demonstrating the importance to properly define the capillary pressure acting on the interface. The first one considers the mean pressure jump at the interface, while the second one uses a machine-learning technique, namely Gaussian process regression, to retrieve the mean curvature of the interface. Those methods are found to be both consistent and in agreement with the results from the literature. Finally, a novel approach that stochastically describes the position of the flow front through a presence distribution is detailed. The spread of the front can be compared to the saturation length, and its value has been found to be small enough to be neglected at upper scale, justifying the use of sharp interface models for similar porous media and flow settings.
... unsaturated permeability are related to the undeformed fiber tows during resin impregnation in the mold-filling process. However, plausible reasons for the observed permeability variation under different flow rate conditions have been reported, such as the void effect and fiber tow deformation problems 34,35 . Tow deformation during the mold filling process is the focus of the current study as one of the contributors to this discrepancy. ...
The potential use of gelatin materials in the liquid composite molding manufacturing (LCM) process was investigated, with specific focus on the reinforcement deformation phenomenon. The adoptability of gelatin as a binder in a composite material with glass fiber for application in the LCM process was evaluated by analyzing the permeability and microscopic structure of the gelatin-coated glass fiber. To assess the tow deformation, the permeability of the non-crimped unidirectional glass fiber mat was evaluated at different flow rates that could be applied in the LCM process. Hysteresis of the permeability was observed as the flow rate increased and decreased, indicative of tow deformation. The permeability of the gelatin-treated glass fiber mat exhibited a relatively smaller variation than that of the untreated glass fiber at the same flow rate. Tow deformation in the untreated and gelatin-treated non-crimped glass fiber mats at different flow rates was evaluated by microscopic analysis and quantified using the tow thickness index. Relatively smaller variations in the permeability and minimal changes in the tow thickness of the gelatin-treated glass fiber mat were observed via microscopic analysis, indicating that gelatin effectively maintained the binding structure of the glass fiber mat.
... Manufacturing of lightweight composites involves complex deformation of fibers that inevitably causes part variability and unintended defects, such as fiber wrinkles, voids, residual stresses, and geometric distortions [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. In Liquid Composite Molding (LCM), flat dry fabrics are draped onto a mold with complex geometries, which can affect the subsequent infusion process and induce fabric wrinkling [16]. ...
Adoption of lightweight composites for structural components is transforming the transportation industry in pursuit of improved performance and better fuel economy. In Liquid Composite Molding (LCM), dry fabric deformation in the draping process gains lots of attention as it affects the fiber orientation, leading to variations in fabric permeability and the resulting final quality of the product due to the change in infusion and curing processes. The lack of robust modeling tools makes the composite manufacturers heavily reliant on trial-and-error approaches to minimize part variability, resulting in high manufacturing costs and limiting innovations for new process and part designs. The current study develops a modeling approach to predict the deformation for dry fabric. In the model, fabric is made of interlacing virtual fiber tows which are represented by Timoshenko beams joint by translational and rotational springs. Dashpots at intersections are used to capture energy dissipation. The proposed model features the simplicity and efficiency in the prediction of shear angle when fabric is subject to 3-dimensional loading. Another highlight of this study is the consideration of characterized relaxation behavior of fabric subject to in-plane shear loading. Cantilever beam bending tests and picture frame tests were carried out to characterize material properties, geometric characteristics, spring stiffness, and damping coefficients. The proposed model was applied to a hemisphere draping model implemented in Abaqus to demonstrate the predictive capability.
