Search

Part I of this two-part paper presented the framework to integrate the simulation of resin flow and stress development during the manufacturing process of composites. In the current paper, the integrated approach developed in Part I for isotropic materials is extended to the case of transversely isotropic materials. Various numerical examples are considered in which the results obtained from the integrated approach are compared to those generated from the previously established models for processing induced stress development. These comparisons serve to elucidate the importance of accounting for the spatial and temporal variations in the resin volume fraction during processing and its effect on stress development. Such effects cannot be investigated in a non-integrated simulation environment where volume fraction variations due to resin flow have to be mapped sequentially from the flow simulation onto the next phase of the process simulation which treats the resin as an elastic or viscoelastic solid. [ABSTRACT FROM AUTHOR]

Process modelling of thermoset matrix composites is typically divided into two distinct and sequential steps: (i) flow-compaction analysis before gelation of the resin when it behaves in a fluid-like manner, and (ii) thermomechanical analysis after gelation when appreciable modulus and thereby stress development occurs. This two-part paper presents a novel approach to integrate the simulation of resin flow and stress development seamlessly during the processing of composites. Part I lays the theoretical foundation for the simpler case of isotropic materials while Part II extends the methodology to the case of transversely isotropic materials. The formulation is implemented in a 2D plane strain finite element code written in MATLAB. Relevant numerical examples are presented to demonstrate both aspects of flow-compaction and stress development throughout the curing process of thermoset matrix composite materials. The effects of resin flow on the development and the final values of residual stresses are investigated. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of resin flow in carbon fiber reinforced polymer by means of small embedded pressure sensors. High-quality carbon fiber reinforced polymer parts require entire impregnation of fibers with resin before resin curing starts. Small piezo-resistive pressure sensors are used to measure the vacuum hold and to track resin flow and pressure elevation inside the composite part. The sensors are placed at different locations in the fiber stacks. Real-time pressure changes are obtained inside the laminate during infusion. To reduce the size of the embedded sensing element, the sensor dies are flip-chipped on a thin printed circuit board. The two component thermoset resin (RIM 035 c) and uni-directional carbon fiber with the alignment of 30 are used in a complex-shaped mold. The result shows that the flip-chipped piezo-resistive pressure sensors can be used in conductive fibers to monitor resin arrival and pressure development in vacuum assisted resin transfer molding infusion processes. The sensors are supplied by a constant current source to compensate the sensitivity reduction if the temperature changes in the curing process. [ABSTRACT FROM AUTHOR]

Compression resin transfer molding (CRTM) is an effective process for the manufacturing of composite parts with large size and high fiber content. The analysis of the resin flow and stress distributions can only be performed by directly solving the coupled flow/deformation equations, but it is difficult to handle the complicated preform deformation models and geometry models; therefore, the simulation precision and application range are extremely limited. In this paper, an alternative approach is introduced to overcome the above problems, in which the preform deformation and the accompanying resin release during the secondary compaction phase are calculated in an additional element associated with each unit of the discretized model geometry instead of solving the coupled governing equations directly, so the complex compaction models can be adopted. Three simulation examples are presented to demonstrate the accuracy and capability of the above numerical approach on velocity-controlled, force-controlled 3D CRTM processes. [ABSTRACT FROM PUBLISHER]

The resin flow behavior in the vacuum assisted resin infusion molding process (VARI) of foam sandwich composites was studied by both visualization flow experiments and computer simulation. Both experimental and simulation results show that: the distribution medium (DM) leads to a shorter molding filling time in grooved foam sandwich composites via the VARI process, and the mold filling time is linearly reduced with the increase of the ratio of DM/Preform. Patterns of the resin sources have a significant influence on the resin filling time. The filling time of center source is shorter than that of edge pattern. Point pattern results in longer filling time than of linear source. Short edge/center patterns need a longer time to fill the mould compared with Long edge/center sources. [ABSTRACT FROM AUTHOR]

The flow of resin into fiber tows is driven by an applied pressure gradient and the capillary pressure, which is dependent on the contact angle between the fibers and the resin as well as the fiber diameter and its arrangement with respect to neighboring fibers. Previous work has reported on methods to calculate the average capillary pressure between two fibers which does not take into account the effect of neighboring fibers in a closely packed tow. This paper introduces a novel method to calculate the average capillary pressure of resin moving through a unit cell containing five fibers in a commonly found fiber arrangement within a fiber tow. Both numerical and analytical solutions are presented, validated, and compared. The role of selected parameters on average capillary pressure is investigated. The influence of packing a unit cell with fibers with different surface treatments is also examined. This work should prove useful in predicting the average capillary pressure of resin moving between fibers and the results can be used to address filling of fiber tows during composites manufacturing and addressing void formation within fiber tows. [ABSTRACT FROM AUTHOR]

Railways, as one of the representative mass transit systems, are vulnerable to highly contagious respiratory diseases due to their operation in densely populated environments. Notably, the current convective heating system creates an environment susceptible to virus transmission within railway vehicles. To improve this situation, there have been attempts to introduce radiant heating systems to reduce the risk of virus transmission and create a comfortable indoor environment. Previous studies focused on developing radiant heating composite material for railway vehicles by incorporating a carbon fiber heating element within a glass fiber composite to enable heat generation through joule heating. However, this development was limited to the specimen level. In contrast, this study aims to demonstrate their applicability and performance for actual railway vehicle parts at the component level. Specifically, resin flow and manufacturability were analyzed to assess applicability to railway vehicles. Additionally, heating performance and heat flow characteristics were evaluated to determine heating effects. Based on these results, it is anticipated that the application of multifunctional composite materials in the railway industry will improve the vulnerability to winter viruses and indoor environments and expand the utilization of multifunctional composite materials in various fields. [ABSTRACT FROM AUTHOR]

In the autoclave curing process of phenolic resin composite at high pressure, uncured resin usually flows into the vacuum pipe through improperly used bleeder and blocks the vacuum orifice. Therefore, there are too many defects formed in the as-prepared composite because not all volatiles can be expelled from the laminate. In order to choosing or manufacturing the bleeder used in this special condition, the resin flow in the bleeder should be carefully investigated. However, the resin flow in the bleeder cannot be observed directly during the autoclave curing process, computer simulation is employed to describe the flow in the bleeder. The simulation results show that i) the resin flow near the vacuum orifice is quite different compared to that far away from the vacuum orifice, the resin can flow through the bleeder near the vacuum orifice within a shorter time; ii) a bleeder made from needle-punched nonwoven material with low porosity, small fibre diameter and small permeability could prevent the resin from flowing into the vacuum pipe in the autoclave curing process. [ABSTRACT FROM AUTHOR]

Liquid molding processes, such as resin transfer molding, involve resin flow through a porous medium inside a mold cavity. Numerical analysis of resin flow and mold filling is a very useful means for optimization of the manufacturing process. However, the numerical analysis is quite time consuming and requires a great deal of effort, since a separate numerical calculation is needed for every set of material properties, part size and injection conditions. The efforts can be appreciably reduced if similarity solutions are used instead of repeated numerical calculations. In this study, the similarity relations for pressure, resin velocity and flow front propagation are proposed to correlate another desired case from the already obtained numerical result. In other words, the model gives a correlation of flow induced variables between two different cases. The model was verified by comparing results obtained by the similarity relation and by independent numerical simulation. [ABSTRACT FROM AUTHOR]

Flow of a catalyzed resin into a fibrous preform is an important step governing the quality of composite parts fabricated using liquid molding techniques. This article presents numerical and experimental investigations on novel means of active flow control to steer the resin flow through the preform so as to eliminate void entrapment and dry spots. The active control is based on locally heating resin to reduce viscosity and, thereby, enhance preform permeation at locations of flow lag in the preform throughout the filling process. A consequence of heating the reacting resin is an accelerated cure reaction that irreversibly increases resin viscosity with cure. A balance between the competing sources of viscosity change form the basis for the model-based control of localized heating. Focusing on a vacuum assisted resin transfer molding (VARTM) process, numerical modeling is coupled to an active control strategy in a simulation environment, and parametric studies are presented over a range of preform lay-ups and constraint on the maximum cure levels at the completion of the filling stage. In addition, the active control system is experimentally implemented and is shown to be successful in fabricating composite panels, without void entrapment or premature resin gelation, while reducing fill time and resin wastage. [ABSTRACT FROM AUTHOR]

This research included the modeling and simulation of the flow of epoxy resin during manufacturing of copper-clad laminates. Three conceptual models were proposed, based on the three resin flow mechanisms during processing: squeezing flow in thin fluid channels, seepage though a permeable medium, and a combination of squeezing and seepage flow. The similarity between the governing equations of each of the models was illustrated using dimensional analysis. The viscosity effect caused by the resin curing process was taken into consideration in the flow models. The results from the simulations provided deep insight into the dependence of the models on the respective geometric and empirical parameters. [ABSTRACT FROM AUTHOR]

Copyright of Ingenius, Revista Ciencia y Tecnología is the property of Universidad Politecnica Salesiana and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper, an enhanced VARTM process is proposed and its pressure effect on resin infusion behavior and composite material performance is studied to reveal the control mechanism of the fiber volume fraction and void content. The molding is vacuumized during the resin injection stage while it is pressurized during the mold filling and curing stages via a VARTM pressure control system designed in this paper. Theoretical calculations and simulation methods are used to reveal the resin's in-plane, transverse, and three-dimensional flow patterns in multi-layer media. For typical thin-walled components, the infiltration behavior of resin in isotropic porous media is studied, elucidating the control mechanisms of fiber volume fraction and void content. The experiments demonstrate that the enhanced VARTM process significantly improves mold filling efficiency and composite's performance. Compared to the regular VARTM process, the panel thickness is reduced by 4% from 1.7 mm, the average tensile strength is increased by 7.3% to 760 MPa, the average flexural strength remains at approximately 720 MPa, porosity is decreased from 1.5% to below 1%, and the fiber volume fraction is increased from 55% to 62%. [ABSTRACT FROM AUTHOR]

The article presents a study which examined the simulation of the reactive mold-filling process with edge effects as well as the influences of the curing reaction and various processing parameters on the resin flow patterns. It found that the resin curing reaction resulted to an increase in the injection pressure and the influencing degree became greater with increasing resin temperature. It noted that there was no evident effect on the resin flow caused by a change in resin viscosity.

The field of application of Glass Fiber Reinforced Polymer expands as well as the size of the component where composite material is applied. Due to the size limitation of the prepreg used, it is difficult to apply 1ply to large parts. Many studies have been reported on the bolt joint that assembles parts and parts for the joint area, butt and overlap design for joining dissimilar materials, and mechanical properties. Although the mechanical properties of the joint areas are important, studies on the microstructure are also needed. In this study, the microstructure was observed by controlling the type of subsidiary materials in the bagging process by applying prepregs of the same composition. It was found that the air and resin flow inside the prepreg acted differently depending on the type of subsidiary material. The flow of resin during curing was inferred from the influence of subsidiary materials and explained by connecting it with the microstructure. The behavior of the resin determined thickness, resin, and void contents of the composite. This flow affects voids in the joint area, causing differences in microstructure and mechanical properties. There was no significant difference in the tensile strength of the laminate specimens manufactured according to the process, but the minimum strength was found in the specimens containing many void contents. The joint specimen showed a decrease in strength as the void content increased. It was discussed that this reduced the adhesive force of the specimen due to the effect of the void generated in the joint area. [ABSTRACT FROM AUTHOR]

Use of composite materials for structural application has greatly flourished in last three decades. Mechanical properties of carbon composite are largely dependent on the processing parameters like processing temperature, compaction pressure, resin flow and fiber orientation. Processing temperature has an important and decisive role in defining the properties of the composites and absence of proper temperature can cause reduced mechanical properties and defects like wrinkles and voids. This study focuses on varying the initial processing temperature for carbon laminates and documents the effect on mechanical properties of the composite produced. The testing range of temperature was specified by the choice of resin. It was found that the mechanical properties like tensile, bending and shear strength increased non-linearly with increasing initial temperature of processing. Increase of fiber volume fraction, fiber weight fraction and density were observed which along with better resin distribution, resin flow and increased laminate compaction can be attributed as key reasons of increased mechanical properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel sensing principle is proposed for micro-flow measurement. • Micro-flow sensor for resin fluidity monitoring between fibers is designed. • The sensor's ability to measure key flow states during composite processing is illustrated. • The sensor is highly sensitive and calibration-free. Abstract The resin micro-flow between fibers influences bubble evacuation and fiber impregnation during the processing of fiber reinforced polymer (FRP) composites. The trapped bubbles and unimpregnated regions within a laminate will develop into voids after the processing, which will impair the structural performance severely. In this study, a new sensing principle of the step-changing difference of capillary pressure was proposed for the micro-flow measurement between reinforced fibers in FRP composites. A highly sensitive and calibration-free micro-flow sensor was designed by simply introducing an optical fiber with super-infiltration polyimide coating along the reinforced fibers. The FRP composite around the optical fiber was regarded as part of the sensing structure. The key resin flow states between fibers were first detected continuously during composite processing. [ABSTRACT FROM AUTHOR]

The vacuum infusion is a process usually applied to manufacture large structures of composite materials, such as wind turbine blades. This work analyzes the macroscopic resin flow through a laminate of fiberglass plies with different orientations, during the filling stage of the vacuum infusion process to manufacture two different pieces. The pressure inside the mold, velocity vectors, and the resin inlet mass flow are studied through a three-dimensional numerical modeling under non-steady conditions validated experimentally. The numerical model simulates each ply of the laminate like an individual porous media and takes into account the stacking sequence of the laminate. The influence of the permeability values of the distribution media and of the fiberglass laminate on the evolution of resin infusion is analyzed. The numerical model reproduces the effects of the stacking sequence and race tracking on the resin flow front. [ABSTRACT FROM AUTHOR]

In this work, the authors present a digital twin (DT) to analyse the manufacturing process of structural composites by using resin transfer moulding (RTM). During RTM, a dry textile preform is impregnated with a polymer resin injected in a closed mould. RTM is one of the most used production methods for high-performance structural composites. The DT is focused on detecting in-homogeneous resin flow produced by race-tracking channels that divert resin flow to the outlet gates of the mould, producing dry spots and lack of impregnation. The DT core contains two surrogate models based on encoder/decoder deep learning architectures, providing the fast/accurate response necessary for interrogation during manufacturing. The first surrogate acts as the disturbance detector, providing the on-the-fly representation of the fabric permeability with the only information gathered by a set of five pressure sensors distributed over the mould surface. The second offers real-time representation of a set of quantities of interests (QoI): namely, the flow progress and the pressure field inside the mould. Training of both surrogates was performed with synthetic data generated by high-fidelity multi-physics simulations of the flow progress in a porous preform by following Darcy's law. Errors in the pressure field predictions of the surrogates are lower than 1 % with consultation time <50 ms, enabling encapsulation in the digital twin. The DT performance was evaluated by comparing the response against a set of RTM experiments for different race-tracking scenarios. The two most relevant novelties of the work are the use of the concept of the instantiated DT, which provides information on the current state of the process from data provided by a network of distributed sensors, and that this DT has been trained exclusively with synthetic data from multiphysics simulations while evaluated against experimental data from injection tests. [ABSTRACT FROM AUTHOR]

Liquid composite molding (LCM) is a class of fast and cheap processes suitable for the fabrication of large parts with good geometrical and mechanical properties. One of the main steps in an LCM process is represented by the filling stage, during which a reinforcing fiber preform is impregnated with a low-viscosity resin. Darcy's permeability is the key property for the filling stage, not usually available and depending on several factors. Permeability is also essential in computational modeling to reduce costly trial-and-error procedures during composite manufacturing. This review aims to present the most used and recent methods for permeability measurement. Several solutions, introduced to monitor resin flow within the preform and to calculate the in-plane and out-of-plane permeability, will be presented. Finally, the new trends toward reliable methods based mainly on non-invasive and possibly integrated sensors will be described. [ABSTRACT FROM AUTHOR]

The resin film infusion (RFI) process is a novel composite molding method for high-fiber content, excellent mechanical properties, low porosity, and adjustable thickness. This review examines two common resin materials used in the RFI process: bismaleimide resin (BMI) and epoxy resin. Furthermore, numerical simulation methods for isothermal and non-isothermal processes in the RFI process are described, focusing on the analysis of the mathematical model of resin flow. Finally, it covers the unique properties of RFI composites and showcases the RFI process's cost-effectiveness and functionality in fabricating composite structures for various applications. The limitations and potential future developments of RFI process molding technology are also summarized. [ABSTRACT FROM AUTHOR]

The excellent properties of advanced composite materials provide great opportunities for making industrial structures large-scale and intelligent. Liquid composite molding process is suitable for manufacturing complex large-scale composite structures and has the potential for low cost and mass production. In present work, the concept of Networked Elements for Resin Visualization and Evaluation network was developed to measure and monitor the manufacturing process in-situ. This paper investigates the capability of piezoelectric lead-zirconate-titanate sensors in the Networked Elements for Resin Visualization and Evaluation network to monitor two important parameters in liquid composite molding process, including the resin flow front and the progress of the reaction. The piezoelectric lead-zirconate-titanate sensor network can be integrated with a composite structure either installed on the interface between the mold and laminates or embedded inside the laminates during the liquid composite molding process. Experimental results demonstrated that the liquid composite molding process can be effectively monitored by the embedded Networked Elements for Resin Visualization and Evaluation network with a piezoelectric lead-zirconate-titanate sensor network. [ABSTRACT FROM AUTHOR]

During autoclave processing of composites for high-performance applications, it is mandatory to limit the porosities, which mainly depend on the hydrostatic pressure in the resin. This pressure, which is not constant during heating being affected either by resin flow either by elastic stress in the fiber stack, can be significantly different from the autoclave pressure. Modeling of resin flow and stress in the fiber stack is a key issue for prediction of the resin hydrostatic pressure, which can be related to void development. Also, the viscosity of the thermosetting matrix is a relevant parameter since it is not constant but evolves during curing going through a minimum and then increasing to an infinite value at gel point. In this work, a viscoelastic model is adopted to calculate the evolution of resin pressure during an autoclave cycle up to gelation, accounting for viscosity and degree of reaction changes. Therefore, the model includes a kinetic and rheological model whose input parameters have been experimentally determined by Differential Scanning Calorimetry and rheological analysis. The predicted resin pressure for three case studies associated to different composite and bleeder thicknesses and reinforcement materials have been discussed. POLYM. ENG. SCI., 57:631-637, 2017. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

The use of glass fiber reinforced plastics (GFRP) in large primary marine structures has noticeably increased due to their favorable stiffness, strength, durability, and manufacturability. However, GFRP construction can become cost-prohibitive at the superyacht-scale (36-60 m) as defects and labor intensiveness increase. In this paper, we presented an automated vacuum assisted resin transfer molding process (VaRTM) that can be integrated into an existing setup for manufacturing recreational composite yachts in the 49-meter range. The objective of automating the system is to reduce defects and labor intensity. The developed automation system consisted of a controller, resin supply lines with valves, and infrared sensors. The control software, valves and sensors were custom developed. The system automatically monitors and adjusts resin flow in the mold in real-time to mitigate flow front variations. The system was used to run three different scenarios common in marine composites manufacturing using VaRTM; a flat plate with consistent ply sequence, a flat plate with varying ply sequence, and a scaled yacht keel section. Results indicated that use of the automated setup improved overall evenness of resin flow and limited unwanted convergence compared to the traditional manual setup. Tensile testing indicated similar mechanical performance but greater variation in the manual sample. Voids were discovered in regions of flow convergence of the manual panel and reflected slightly more varied tensile properties as compared to automated panels. POLYM. COMPOS., 38:2411-2424, 2017. © 2015 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

Studies were carried out on the storage life of Room Temperature (RT)-curable pre-pregs comprising of two varieties of bi-functional epoxy resins (imported resin system and an equivalent grade of indigenous resin system) as matrices and bi-directional glass fabric as reinforcement. The hand-made pre-pregs were stored at sub-ambient temperature (-18°C). The resin flow of pre-preg was determined as a function of storage period. Composite laminates were vacuum molded using the pre-pregs taken out of the deep freezer. The composite specimens were characterized for their thermal (Tg) as well as mechanical properties. The properties obtained were compared with the properties of wet layed-up composites fabricated without the usage of pre-impregnated plies. [ABSTRACT FROM AUTHOR]

The finite element formulation is developed to solve the flow and compaction problems to simulate the resin flow and laminate compaction during the hot-pressing process of fiber-reinforced composite laminates. The numerical flow-compaction model is based on the effective stress formulation, the continuity equations, and Darcy's flow theory. Two methods are used to calculate the variation of the laminate thickness, the simulated results validate the relationship of fiber motion and resin flow velocity. Together with the post-processor software. the visual laminate deforming process is realized through the node moving. The comparison between the predicted and experimental data shows that the program is reliable to predict the laminate thickness and the final fiber volume fraction distribution in the thickness direction. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Natural Fibers is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A scaled, 7.5-mm thick, unidirectional glass/epoxy wind turbine spar cap cured in a vacuum-assisted oven was found to have attained non-uniform thickness along its length. Edge deformations were severe, leading to noticeable edge curvature even at the vacuum pressure. These unforeseen discrepancies could only be predicted and/or dealt beforehand through a process simulation that integrates the complete processing physics. A fully coupled numerical simulation of composites manufacturing was established and implemented for a portion of a spar cap in multiphysics finite element software. Phenomena such as resin flow-induced compaction and cure-induced deformation were captured. The simulation results indicated that even though the distorted edge of the laminate is trimmed off, there will still be some curvature left within the part. It was noted that simulating percolation flow of resin alone leads to less accurate deformation predictions. Therefore, a method to include shear flow-induced deformation of the resin-saturated fiber beds were proposed and implemented. Such a fully coupled and integrated procedure is useful for optimizing process parameters to achieve intended final part with accurate dimensions and minimal manufacturing-induced defects or deformities. [ABSTRACT FROM AUTHOR]

Voids are the most common process-induced defects in composite laminates fabricated by vacuum assisted resin transfer molding (VARTM). Reduction or total elimination of these defects is essential for the improved performance and long-term durability of the structural composites. This study introduces a novel method that reduces the void content in VARTM laminates to below 1% by compacting the fibrous mat before infusion. The compaction is achieved by applying magnetic pressure on the vacuum bag by either stationary or moving magnets which are removed before the resin infusion. To assess the effectiveness of the proposed method, 6-, 12-, and 18-ply random mat glass/epoxy laminates are fabricated by VARTM using compacted and uncompacted mats and their properties are compared. In addition, different sets of magnets are used to investigate the effect of compaction levels on the resin flow and the quality of the final part. The placement of stationary magnets on the entire vacuum bag surface is practical for fabrication of small parts. For medium to large parts, however, magnets with a smaller footprint can be moved to apply the compaction pressure over a larger vacuum bag surface. The results show that by applying compaction pressure of 0.2 MPa or higher either by stationary or moving magnets on the dry preforms, the void volume fraction was decreased by 65%–95% to 0.1%–0.8% in all laminates. [ABSTRACT FROM AUTHOR]

Copyright of Basic Sciences Journal of Textile Universities / Fangzhi Gaoxiao Jichu Kexue Xuebao is the property of Basic Sciences Journal of Textile Universities and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study analyses the influence of the random filament arrangement in fibre bundles on the resin flow behaviour. Transverse steady-state resin flow that occurs behind a liquid resin flow front was simulated numerically through statistically equivalent micro-structures at high-fibre volume fractions, Vf > 0.6, as observed in fibre bundles. The need of applying a minimum gap distance between neighbouring filaments was overcome by automated local mesh refinement. The derived permeability values showed significant scatter. Convergence of these values was determined at a ratio of flow length to filament radius greater than 20 for all three analysed fibre volume fractions. Mean permeabilities were between 6 and 10 times lower than those predicted for a hexagonal fibre array. A statistical model is proposed, which is able to predict the scatter of observed permeabilities based on simple micro-structural descriptors. [ABSTRACT FROM AUTHOR]

Shortening the curing time is critical to improve the processing efficiency of composites. In this paper, unidirectional carbon fibre-reinforced rapid curing epoxy composite laminates were fabricated by vacuum-assisted resin injection moulding (VARIM). Different rapid curing processes (namely P80, P85, and P90) were employed, which preheating temperatures were 80, 85 and 90 °C, respectively. Different preheating temperatures of mould and fibre preform were conducted, to demonstrate the effects on the properties and processing time of the composites. In addition, a slow curing process (N80) was investigated to verify the effect of rapid curing on the mechanical properties of the composites. The relationships among preheating temperature, curing cycle and properties of the composites were analyzed. The results showed that the preheating temperature had obvious effects on the total cycle time and properties of the composites. The cycle time of the P80 process was 947 s, whereas that of the P90 process was 702 s. However, nonuniformity of the mechanical properties along the resin flow direction was more obvious for the P90 process, and more voids formed in the resin outlet region. Composites fabricated by the P80 process showed comparable mechanical properties and processing quality to those from the N80 process. It is suggested that a rapid curing process with proper preheating temperature is acceptable to improve the processing efficiency. [ABSTRACT FROM AUTHOR]

This paper presents an experimentally validated model to simulate the nonisothermal resin infusion and cure processes in a relatively large and thick composite laminate fabricated using vacuum-assisted resin transfer molding. Compaction effects were accounted for by using a step-wise scheme wherein the panel was divided into three discrete zones along the flow direction, with each zone being assigned different porosities and other material properties. The experimentally observed dynamic evolution of the resin flow front profile due to permeability difference between the high-permeable infusion medium and the glass-fiber preform as well as the heat transfer in the preheated system was captured accurately. Both model predictions and experimental measurements indicate subtle variation in the spatiotemporal distributions of temperature and degrees of resin cure from the infusion stage can result in large differences in the resin cure profile across the laminate, which may cause undesirable residual stresses in large composites. [ABSTRACT FROM AUTHOR]

In the RTM light composite manufacturing process, inorganic fillers are commonly added to the resin to reduce cost and alter the final composite properties, especially rigidity, even though they also adversely affect processability. The aim of this study is to evaluate resin characteristics, reinforcement permeability, and mechanical properties of the composite and analyze the detrimental effects when a variable amount of calcium carbonate (CaCO3) is added to the resin. The addition of calcium carbonate increased the viscosity and gel time of the resin and considerably decreased the permeability of the reinforcement and therefore the expected process productivity. Besides, Barcol hardness, short-beam strength, and elastic modulus increased for higher CaCO3 content, whereas Izod impact, flexural, and tensile strengths decreased. Besides, the coarser CaCO3 filler particles managed to penetrate only partially into the fiber-rich layer of the combination mat used, which comprised of a PP flow media core and glass fibers at the surface. [ABSTRACT FROM PUBLISHER]

Toughened epoxy resin is one of the most important matrices in composite structural materials. In this article a one-dimensional resin flow/fiber compaction model was used for analysis of the consolidation of a toughened epoxy resin 5228/T700S carbon fiber laminates. The laminate thickness and the fiber volume fraction distribution of cured laminates under different cure cycles were investigated both from the experimental measurements and from the numerical simulation. The calculated and experimental results are in good agreement for all the studied cases. A significantly uneven degree of consolidation along the laminate thickness direction is observed, and it is difficult to improve by altering cure cycle. These results are valuable for the study of the performance of composite parts, provided that uneven distribution of fibers does affect some properties of composite materials. [ABSTRACT FROM AUTHOR]

Vacuum assisted resin transfer molding (VARTM) is ideal for the manufacture of large-scale composite structures. However, gravitational effects on flow behavior can be significant in increasingly tall structures. In this study, an analytical solution incorporating the gravitational effects is developed to predict the flow and pressure distributions of uniform thickness preforms under vacuum infusion conditions. Injection scenarios of preforms of various lengths and inclination angles ranging from horizontal to vertical are studied. Nondimensional process parameters in terms of the resin fill time, mold angle, permeability, radius and length of injection tubes, and preform cross-sectional area for horizontal, downward, and upward injection scenarios are considered. The analytical results show good agreement with the experimental data collected in horizontal and vertical infusions. The parametric study provides insight into the design and optimization of the VARTM process for infusion of tall composite structures. [ABSTRACT FROM AUTHOR]

The paper gives a set of basic relations characterizing the phenomena of viscous polymer resin flow through fiber reinforcement and the resin curing process. We describe the technological process of manufacturing composite structures. The influence of the resin curing process on values of residual stresses in composite constructions is analyzed taking into account two components: thermal shrinkage and chemical shrinkage of resins. For cases of 2-D structures, the method of formulating such tasks has been demonstrated. The types of design variables appearing in the optimization problems in this area are also presented. The 2-D optimization problems have been formulated. Various optimization problems are solved in order to demonstrate the influence of discussed relations on values of residual stresses and curing processes of thermosetting resins. [ABSTRACT FROM AUTHOR]

As the demand for fiber-reinforced composite (FRC) has increased in various industries, composite materials have been manufactured in larger sizes and more complex shapes. Since the FRC has been manufactured in such larger and more complex shapes, wettability, one of the important factors in FRC manufacturing efficiency, has been the focus of many researchers. This paper explores various evaluation methods of the wettability between fiber and polymer matrix. Generally, work of adhesion, capillary, and permeability methods have been used to evaluate the wettability parameters between the fibers and the polymer matrix. These three parameters exhibit different scales of measurements such as surface energy, viscosity of the polymer, the fiber volume fraction, fiber orientation, and so on. Future research may include complementary studies between these evaluation methods. [ABSTRACT FROM AUTHOR]

We investigate the unsaturated resin flow behavior in a dual scale porosity preform by observing the pressure distribution and the void content. The experimental data show that the pressure profile in the unsaturated flow is nonlinear with positive curvature whereas that in the saturated flow is linear as expected from the classical Darcy's law. To address this issue, the governing equation for mass conservation is modified by introducing a mass sink term. Eventually, it has been found that the discrepancy between the unsaturated and saturated permeability values comes from a misinterpretation of the pressure gradient at the flow front in the unsaturated permeability measurement method and the permeability for a given preform is a unique value regardless of measurement method or flow condition. Based on this investigation, the ratio of unsaturated permeability to saturated permeability is represented as a dimensionless number in terms of void content. [ABSTRACT FROM AUTHOR]

The vacuum infusion is a process usually applied to manufacture large structures of composite materials, such as wind turbine blades. The specific stiffness and weight ratio required by these structures can be achieved by manufacturing sandwich composites. The forecast by numerical simulation of the resin infusion flow is an indispensable tool to design and optimize the manufacturing process of composite. Present work analyzes by numerical simulation the mold filling process of a sandwich composites, performed by fiberglass plies with different fiber orientations and a perforated core. The flow through a single perforation of the core is analyzed and the influence of the permeability values of fiberglass on the volume flow through core perforations is determined. In order to reduce the computing costs, a transfer function to simulate the flow through the perforations is developed and integrated in the numerical code by computational subroutines. A 3D numerical modeling of a sandwich composite, in which the flow through the core perforations is simulated via computational subroutines, is carried out and experimentally validated. [ABSTRACT FROM AUTHOR]

This research presents a case study of production monitoring on an aerospace composite component: the hinge arm of the droop nose mechanism on the Airbus A380 wing leading edge. A sensor network composed of Fibre Bragg Gratings, capacitive sensors for cure monitoring and thermocouples was embedded in its fibre reinforced lay-up and measurements were acquired throughout its Resin Transfer Moulding production process. Two main challenges had to be overcome: first, the integration of the sensor lines in the existing Resin Transfer Moulding mould without modifying it; second, the demoulding of the component without damaging the sensor lines. The proposed embedding solution has proved successful. The wavelength shifts of the Fibre Bragg Gratings were observed from the initial production stages, over the resin injection, the complete curing of the resin and the cooling-down prior to demoulding. The sensors proved to be sensitive to detecting the resin flow front, vacuum and pressure increase into the mould and the temperature increase caused by the resin curing. Measurements were also acquired during the post-curing cycle. Residual strains during all steps of the process were derived from the sensors' wavelength shift, showing values up to 0.2% in compression. Moreover, the capacitive sensors were able to follow-up the curing degree during the production process. The sensors proved able to detect the resin flow front, whereas thermocouples could not measure an appreciable increase of temperature due to the fact that the resin had the same temperature as the mould. [ABSTRACT FROM AUTHOR]