Vacuum Assisted Resin Transfer Molding Process Research Articles

Numerical study of filling strategies in vacuum assisted resin transfer molding process

Abstract During the filling process of vacuum assisted resin transfer molding (VARTM), the infusion pressure gradient causes the resin flow and preform thickness variation. Even after the resin infusion discontinues, the resin keeps on flowing until the unnecessary resin is removed. In this study, a one-dimensional flow model coupled to the preform deformation is numerically analyzed to assess the influences of various processing scenarios on the infusion and post-infusion stages. The numerical model is implemented using a finite difference method. Results show that two strategies effectively reduce the filling process. One is to infuse less excess resin and the other is to turn the inlet into the additional vent. For a typical process using a one-sided vent, the theoretically optimum scenario is to infuse the exact required resin volume into the preform. From a practical standpoint, excess resin infusion is inevitable and a robust scenario is proposed by integrating the concept of fully filled preform and two strategies. Additional cases are performed using a vacuum assisted compression RTM (VACRTM) process for comparison purposes. Through the numerical work, a tool for optimization of the VARTM process is provided to reduce the filling process, resin waste and variability in the final composite part.

Effects of the addition of a cover mold on resin flow and the quality of the finished product in vacuum‐assisted resin transfer molding

For vacuum‐assisted resin transfer molding (VARTM), we propose adding a cover mold, inserted between the distribution medium and the peel ply, to achieve a higher fiber volume fraction in the final product. As the conventional VARTM process does not use a cover mold, improved processes using different rigid covers were explored. A three‐dimensional digital image correlation system was developed to monitor the thickness evolution of the vacuum package during the infusion stage. This system was validated as a full‐field displacement test. The results demonstrate that there are three advantages to using a cover mold. First, in the filling stage, a rigid cover mold can prevent shrinkage of the part at the resin flow front, and even cause slight expansion of the unsaturated part. This improves the resin flow and shortens the time required for complete infusion. Second, a cover mold can limit the amount of excess resin needed to infuse the saturated part. Third, in the postfilling stage, the cover mold can be used to accelerate extrusion of the excess resin in the package. The overall effect is to increase the fiber volume fraction in the final product. POLYM. COMPOS., 37:1435–1442, 2016. © 2014 Society of Plastics Engineers

Optimization of interlaminar shear strength behavior of anodized and unanodized ARALL composites fabricated through VARTM process

Aramid Aluminum laminates (ARALLs), which belong to the family of fiber metal laminates (FML’s) are prone to interlaminar shearing because of weak bonding between Aluminium and Kevlar layers. Moreover standard fabrication procedure of these composites is to use unidirectional fiber prepregs with Aluminium alloy sheets. The fabrication thus involves expensive semi prepared materials (prepregs) followed by autoclaving. Over the recent years VARTM (Vacuum assisted resin transfer molding) has emerged as a viable and low cost technique for composites fabrication. In this paper an alternative fabrication procedure for ARALL composites using VARTM has been presented. For this purpose Aluminium 2024 T3 alloy and plain woven Para-Aramid (Kevlar 49 from DuPont) fibrous tow sheets were used to make ARALL composites. ARALL comprises of one sheet of Kevlar in the center and two layers of Aluminum on its two sides. Two types of Aluminium sheets were prepared i.e., anodized and unanodized. Specimens were prepared using VARTM technology. Two types of post curing treatments were chosen. One group of specimens was post cured at 100 °C while the other group was left to cure at room temperature. T-peel tests were then conducted using ASTM D1876 standard on ARALL specimens thus prepared. This research study entails anodization and curing/post curing for enhancement of interfacial bonding so as to suppress interfacial debonding. Various parameters in this respect have been varied and their effect on the interfacial bond strength and thus on the Mode-I fracture toughness has been quantized. Experimental results, electrochemical characterization and optical/SEM observations of delaminated surfaces have established that anodization coupled with post curing results in an optimized interface between Aluminium alloy and Para-Aramid sheets. The optimization scheme described in this paper can be used to manufacture ARALL composites through low cost VARTM technology.

Performance Evaluations of Carbon/Glass Hybrid Polymer Composites

In this work, the influence of hybrid effect on carbon and glass fiber reinforced polymer (FRP) on the mechanical performance for structural application was studied. The hybrid fiber reinforced polymer (FRP) composites made from woven E-glass and carbon fibers with epoxy resin. The FRP hybrid composites were fabricated using vacuum-assisted resin transfer moulding process, which is capable of producing constant thickness with high volume fractions of composite panels compared to that of traditional wet hand lay-up method. Mechanical performance of the FRP hybrid composites were evaluated against full carbon or glass fiber reinforced polymer composites. Important properties such as tensile strength, flexural strength and volume fraction of reinforcement were determined according to the ASTM standards. It was found that the mechanical properties of carbon-glass hybrid composites exhibited significant improvement in term of strength and strain respectively compared to that of full glass FRP composites and full carbon FRP composites.

Investigation into property control of VaRTM composites by resin infusion process

This paper proposes a property control method in vacuum-assisted resin transfer molding (VaRTM) using porous mold process (PMP) to fabricate carbon fiber-reinforced plastics (CFRP) composites. Low-cost VaRTM process generally induces the variation in quality and properties of fabricated composites, depending on infusion and curing process, dimension and configuration of stacked fabrics, etc. and involves difficulty in control of the properties of fabricated composites. As resin content in the composites can be easily controlled in VaRTM process combined with PMP, this paper investigates the effect of infused resin content on the final mechanical properties of CFRP. It is demonstrated that volume fraction of carbon fibers and the resultant mechanical properties of CFRP can be controlled by the infusion process control. Finally, application of the present control method to the manufacturing of a complex CFRP panel with thickness variation is demonstrated. It is concluded that the measured mechanical properties fit well with the designated properties.

One-dimensional heat transfer study of a fiber-reinforced wind epoxy composite system in vacuum assisted resin transfer molding process

To investigate the influence of curing behavior of a wind-epoxy resin in vacuum assisted resin transfer molding (VARTM) process, numerical analysis of the heat transfer study of VARTM process was established to characterize temperature distribution in one dimension by directly solving heat equation and was compared with the result of experiment. Differential scanning calorimeter (DSC) was applied to test curing kinetic parameters of the epoxy system, which was required to evaluate internal thermal source and analyze heat transfer equations. Two models, such as nth order curing model and autocatalytic model, were established to solve the heat transfer equation. Combining the theoretical results with nth order curing model and experiment, it can be known that in early stage, temperature distribution correlates well with the experiment results due to the dominant chemical-controlled reaction, while great discrepancy appears in the latter stage due to diffusion-controlled reaction taking over. The result of the heat equation solved by autocatalytic model correlates well with the experiment results. POLYM. COMPOS., 35:1031–1037, 2014. © 2013 Society of Plastics Engineers

A Two-layer Model for the Simulation of the VARTM Process with Resin Distribution Layer

Vacuum assisted resin transfer molding (VARTM) is one of the important processes to fabricate high performance composites. In this process, resin is drawn into the mold to impregnate the fiber reinforcement to a form composite. A resin distribution layer with high permeability was often introduced on top of the fiber reinforcement to accelerate the filling speed. Due to the difference of the flow resistance in the resin distribution layer and the reinforcement as well as the resulting through thickness transverse flow, the filling flow field is intrinsically three-dimensional. This study developed a two-layer model with two-dimensional formulation to simulate the filling flow of the VARTM process with a resin distribution layer. Two-dimensional flow was considered in each layer and a transverse flow in the thickness direction was estimated between the two layers. Thermal analysis including the transverse convection was also performed to better simulate the temperature distribution.

Flow Characteristics of Vacuum Assisted Resin Transfer Molding Process Depending on the Capillary Phenomenon

Reducing the cost of composite material production is significant for expanding its usage and application in many ways, such as in the fields of aerospace, aviation, ocean industry and so on. To do this, It is important to minimize the production process of the material and to decrease the amount of scraps or any unnecessary particles. The Vacuum Assisted Resin Transfer Molding (VARTM) process, which is known for having many advantages, has become recognized as one of the most low-cost manufacturing model. VARTM process can be divided into three main steps: performing, resin filling and hardening steps. The most important step among all these three steps is the Resin Filling stage, a process when resin is impregnated into the mat. Mostly, Resin Filling stage is greatly affected by the level of permeability, a characteristic of stiffener due to pneumatic resistant nature in the process. Other factors such as viscosity, technological vacuuming, or even stiffening process itself could also influence the production as well. During Resin Filling stage, Resin tends to spread out in the center first because of capillary phenomenon. In this research, the researchers examined the mechanical property and the pneumatic nature of Resin by dividing the pneumatic movement of the Resin into sections. Based on this result, the researchers found the correlations between the capillary phenomenon and Resin impregnation, and analyzed the movement mechanism in Resin filling stage.

Cure Cycle Effect on High-Temperature Polymer Composite Structures Molded by VARTM

This paper presents an analytical and experimental investigation of cure cycle effect on carbon-fiber reinforced high-temperature polymer composite structures molded by vacuum assisted resin transfer molding (VARTM). The molded composite structure consists of AS4-8 harness carbon-fiber fabrics and a high-temperature polymer (Cycom 5250-4-RTM). Thermal and resin cure analysis is performed to model the cure cycle of the VARTM process. The temperature and cure variations with time are determined by solving the three-dimensional transient energy and species equations within the composite part. Several case studies were investigated by the developed analytical model. The same cases were also experimentally investigated to determine the ultimate tensile strength for each case. This study helps in developing a science based technology for the VARTM process for the understanding of the process behavior and the effect of the cure cycle on the properties of the molded high-temperature polymer composites.

VaRTM process of composites using porous mold

This paper introduces Porous Mold Process (PMP) as a reliable low-cost manufacturing process of fiber-reinforced composites. PMP using porous aluminum is applied to the vacuum-assisted resin transfer molding (VaRTM) process of carbon fiber reinforced plastics (CFRPs). Experimental evaluation on resin infusion behavior and quality and mechanical properties of the cured plates is performed with varying the dimensions of the plates. The results show that quality and mechanical properties of the cured plates using PMP are satisfactory, stable, and almost independent of plate dimensions. It is concluded that PMP provides a reliable and knowhow-less resin infusion process of composite materials.

Elevated-temperature vacuum-assisted resin transfer molding process for high performance aerospace composites

Vacuum-assisted resin transfer molding (VARTM) is commonly used for general temperature applications (<150 °C) such as boat hulls and secondary aircraft structures. With growing demands for applications of composites in elevated temperature environments, significant cost savings can be achieved by employing the VARTM process. However, implementation of the VARTM process for fabricating elevated temperature composites presents unique challenges such as high porosity and low fiber volume contents. In the present work, a low cost and reliable VARTM process is developed to manufacture elevated temperature composites for aerospace applications. Modified single vacuum bagging infusion and double vacuum bagging infusion processes were evaluated. Details of the method to obtain high quality composite parts and the challenging issues related to the manufacturing process are presented. Density and fiber volume fraction testing of manufactured panels showed that high quality composite parts with void content less than 1% have been consistently manufactured. A property database of the resin system and the composites was developed. A three-dimensional mathematical model has also been developed for flow simulation and implemented in the ABAQUS finite element package code to predict the resin flow front during the infusion process and to optimize the flow parameters. The results of the present study indicate that aircraft grade composite parts with high fiber volume fractions can be manufactured using the developed elevated temperature VARTM process. © 2013 Society of Chemical Industry

Thermomechanical properties of alkali treated jute‐polyester/nanoclay biocomposites fabricated by VARTM process

AbstractA systematic study was carried out to investigate the effect of alkali treatment and nanoclay on thermomechanical properties of jute fabric reinforced polyester composites (JPC) fabricated by the vacuum‐assisted resin transfer molding (VARTM) process. Using mechanical mixing and sonication process, 1% and 2% by weight montmorillonite K10 nanoclay were dispersed into B‐440 premium polyester resin to fabricate jute fabric reinforced polyester nanocomposites. The average fiber volume was determined to be around 40% and void fraction was reduced due to the surface treatment as well as nanoclay infusion in these biocomposites. Dynamic mechanical analysis (DMA) revealed enhancement of dynamic elastic/plastic responses and glass transition temperature (Tg) in treated jute polyester composites (TJPC) and nanoclay infused TJPC compared with those of untreated jute polyester composites (UTJPC). Alkali treatment and nanoclay infusion also resulted in enhancement of mechanical properties of JPC. The maximum flexural, compression, and interlaminar shear strength (ILSS) properties were found in the 1 wt % nanoclay infused TJPC. Fourier transform‐infrared spectroscopy (FT‐IR) revealed strong interaction between the organoclay and polyester that resulted in enhanced thermomechanical properties in the composites. Lower water absorption was also observed due to surface treatment and nanoclay infusion in the TJPC. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Influences of moisture absorption and chemical treatments on the resin flow characteristics of natural fibre nonwoven mats

A major challenge for the use of natural fibres in polymeric composites is their incompatibility with commonly used matrices, causing weak interfaces of the final composites. Many surface treatments to natural fibres have been proposed to eliminate or reduce these problems. In this paper, we evaluate the influences of three commonly used natural fibre chemical treatments on the resin flow characteristics of flax fibre nonwoven mats in a vacuum-assisted resin transfer moulding process. The alkalization treatment significantly increases the in-plane permeability and flow anisotropy of the natural nonwoven mat due to changes in fibre diameter, fibre surface tension and mat structure. The effects of silane and acetylation treatments on resin flow are much smaller. It is well known that in comparison with glass fibre, natural fibres can absorb a large amount of moisture from surrounding air. The absorption of moisture causes a considerable reduction in the in-plane permeability of natural fibre nonwoven mats.

Bubble development in a polymeric resin under vacuum

AbstractUnderstanding the gas diffusion and evaporation behavior in a polymeric resin under vacuum is of great importance because many types of polymer and composite products are manufactured by applying a vacuum to the production system. This article proposes a theoretical model that can describe bubble growth under vacuum by combining the mechanisms of gas diffusion and evaporation. To confirm such a model, we carried out experimental analyses including evaporation experiments with a bell jar or a tube as well as vacuum‐assisted resin transfer molding (VARTM). Particularly in the VARTM process, it was identified that many bubbles were nucleated and grew at the fiber‐matrix interface due to the applied vacuum pressure. Those results suggest that more attention should be paid to vacuum‐assisted material processing to prevent bubbles from existing in the final products. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

Use of eco‐friendly epoxy resins from renewable resources as potential substitutes of petrochemical epoxy resins for ambient cured composites with flax reinforcements

AbstractIn the last years, some high renewable content epoxy resins, derived from vegetable oils, have been developed at industrial level and are now commercially available; these can compete with petroleum‐based resins as thermoset matrices for composite materials. Nevertheless, due to the relatively high cost in comparison to petroleum‐based resins, their use is still restricted to applications with relatively low volume consumption such as model making, tuning components, nautical parts, special effects, outdoor sculptures, etc. in which, the use of composite laminates with carbon, aramid and, mainly, glass fibers is generalized by using hand layup and vacuum assisted resin transfer molding (VARTM) techniques due to low manufacturing costs and easy implementation. In this work, we study the behavior of two high renewable content epoxy resins derived from vegetable oils as potential substitutes of petroleum‐based epoxies in composite laminates with flax reinforcements by using the VARTM technique. The curing behavior of the different epoxy resins is compared in terms of the gel point and exothermicity profile by differential scanning calorimetry (DSC). In addition, overall performance of flax‐epoxy composites is compared with standardized mechanical (tensile, flexural and impact) and thermal (Vicat softening temperature, heat deflection temperature, thermo‐mechanical analysis) tests. The curing DSC profiles of the two eco‐friendly epoxy resins are similar to a conventional epoxy resin. They can be easily handled and processed by conventional VARTM process thus leading to composite laminates with flax with balanced mechanical and thermal properties, similar or even higher to a multipurpose epoxy resin. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

3D printed tooling for vacuum-assisted resin transfer moulding

Three-dimensional printing (3DP) is widely considered to be one of the low-cost additive manufacturing (AM) processes. In this paper, the suitability of 3DP for making tooling for the vacuum-assisted resin transfer moulding (VARTM) process is considered. This combination has potential advantages, since VARTM has significant prototyping benefits if it can be combined with a fast and low cost tooling option. This paper presents a new process chain for the manufacture of closed mould composite parts using the VARTM process. It will be shown that 3DP tooling is significantly less accurate than CNC machined tooling, but there is a cost and time advantage to making tooling with 3DP. The mould life is also limited to typically 15 to 30 parts since significant wear occurs in the manufacturing process. Quantitative data are presented to show the effect of treating the mould surface to improve the surface roughness and to determine the mould life. An aspect often lacking in AM research is cost estimation. Here, the first cost model for rapid tooling for VARTM using 3DP moulds is presented and compared to actual results. It is shown that the model is suitable for design for manufacture analysis.

The Research on Flame Retardant Wind Turbines Nacelle Made through VARTM Process

During the process of Vacuum Assisted Resin Transfer Molding（VARTM）making flame retardant wind turbines nacelle, the viscosity of unsaturated polyester resin（UPR）with reactive flame retardant groups is too large to be used in VARTM process. In this paper, a large amount of tests were conducted by the way of adding flame retardant of Dimethyl methyl phosphate(DMMP) so as to make the resin fit for VARTM processing properties requirements as well as increase its flame retardant properties to a higher level. The results showed that, when the content of DMMP was 12%, the resin could be provided with lower viscosity with a reduction of 50.3%, making it possible for the resin to be used in vacuum import process. When the content of DMMP reached 12%, LOI of the casting body reached 31.6, with LOI of glass fiber reinforced plastic of 37.0%, the vertical burning classification of which reached V-0 level without significant drop on mechanical properties of fiberglass reinforced plastics(GFRP). Meet the requirements and provide a good material for flame-retardant wind turbines nacelle.

The Research on Flame Retardant Wind Turbines Nacelle Made through VARTM Process

During the process of Vacuum Assisted Resin Transfer Molding（VARTM）making flame retardant wind turbines nacelle, the viscosity of unsaturated polyester resin（UPR）with reactive flame retardant groups is too large to be used in VARTM process. In this paper, a large amount of tests were conducted by the way of adding flame retardant of Dimethyl methyl phosphate(DMMP) so as to make the resin fit for VARTM processing properties requirements as well as increase its flame retardant properties to a higher level. The results showed that, when the content of DMMP was 12%, the resin could be provided with lower viscosity with a reduction of 50.3%, making it possible for the resin to be used in vacuum import process. When the content of DMMP reached 12%, LOI of the casting body reached 31.6, with LOI of glass fiber reinforced plastic of 37.0%, the vertical burning classification of which reached V-0 level without significant drop on mechanical properties of fiberglass reinforced plastics(GFRP). Meet the requirements and provide a good material for flame-retardant wind turbines nacelle.

Effects of vacuum pressure, inlet pressure, and mold temperature on the void content, volume fraction of polyester/e-glass fiber composites manufactured with VARTM process

Vacuum-assisted resin transfer molding (VARTM) process is one of the liquid composite molding (LCM) processes aimed at producing high-quality composite parts. The void content and fiber volume fraction of a VARTM part can be affected by many parameters and is critical to the mechanical properties and the quality of the part. In this paper, a series of experiments were conducted with a heated dual pressure control VARTM setup for investigating the effects of vacuum pressure, inlet pressure, and mold temperature on the void content and fiber volume fraction of polyester/E-glass fiber composite. It was found that stronger vacuum and higher mold temperature can better control and increase the fiber volume fraction; however, such a combination of strong vacuum and high mold temperature may also require a reduced inlet pressure for minimizing the void content. The need of pressure reduction can be explained with the compatibility between Darcy's flow and capillary flow in the fiber preform and can be calculated based on the room temperature VARTM results. The experimental results suggest that high mold temperature, high vacuum, and appropriately reduced inlet pressure can produce a VARTM part with high fiber volume fraction and low void content.

The Thickness and the Inerior Quality of Composite Panel in the Vacuum Assisted Resin Transfer Molding Process

The objective of this paper was focused on predicting the thickness and the interior quality of carbon fiber composite panel during the vacuum assisted resin transfer molding (VARTM) process. The character of the VARTM process determined that it was low cost. A panel made of Epoxy resin, and carbon fibers, was used as the simplest article to experiment and except routine items, the thickness and the interior quality was focused. In the process, the flow front of the resin was record using a digital camera. Darcy’s law was the model of resin flow. The results showed that the flow front history would reach unanimous, thickness near the edges was difficult to control, and most of the porosity came from the injection line where more resin cumulated.