Vacuum Assisted Resin Transfer Molding Process Research Articles

In-situ resin flow monitoring in VaRTM process by using optical frequency domain reflectometry and long-gauge FBG sensors

The vacuum-assisted resin transfer molding (VaRTM) process has attracted increased attention because of its ability to provide fast production times for large structures while maintaining a high quality. However, the occurrence of process-induced defects during the VaRTM process significantly affects the mechanical properties of the composites, resulting in a decrease in the reliability of the process. Therefore, flow monitoring should be performed during the manufacturing process to eliminate process-induced defects, such as dry spots and unimpregnated areas in the preform.Herein, we report a facile method for monitoring resin flow using a distributed strain sensing method during the VaRTM process. For the distributed strain sensing method, optical frequency domain reflectometry (OFDR) and a long-gauge fiber Bragg grating (FBG) sensor were used simultaneously. To analyze the change in the sensor signal according to the resin impregnation state, the strain along the in-plane direction of the preform during the VaRTM process was investigated through a numerical simulation and compared with the strain change measured by the OFDR system. The strain rate from the FBG sensor showed a positive value in the impregnated region but a negative value in the unimpregnated region, which means that the point at which the reversal of the strain rate occurs is the same as the position of the flow front. Thus, not only the flow front over the entire gauge length but also the approximate position and size of the unimpregnated area were accurately monitored.

Dolomite dust filled glass fiber reinforced epoxy composite: Influence of fabrication techniques on physicomechanical and erosion wear properties

AbstractThis article investigates the effect of fabrication techniques on the physical, mechanical, and erosion wear properties of glass fiber reinforced dolomite dust‐filled epoxy composites. The composites were fabricated by hand layup and vacuum‐assisted resin transfer molding (VRTM) techniques with fixed glass fiber (20 wt%) and varying dolomite dust (0 to 15 wt%) with epoxy resin. In physical properties, the experimental density consistently increased with the increase in the dolomite hand layup and the VRTM process; in opposite the voids content increased in the hand layup process and decreased in the VRTM process. In mechanical properties, the hardness, impact energy, and interlaminar shear strength increases while tensile and flexural strength consistently decreases with dolomite dust content. Using Taguchi's optimization technique, the erosion wear of the fabricated composites was also evaluated at different impingement angles, impact velocities, and erodent sizes. Erosion test results indicate that the VRTM process fabricated composite has minimum erosion wear compared to the hand layup process. The eroded surfaces were studied using a scanning electron microscope to understand the erosion behavior of particulate‐filled fiber reinforced polymer composites.

Low Velocity Impact Behaviour Analysis of Different Fibre Stacking Sequences of Glass Fibre Reinforcement Composite.

Furthering understanding the damage deformation behaviour involved in the impact test of Fibre-reinforced composite material is important in designing for the structural components. Thus, this study presents the damage effect of different stacking sequence of glass fibre reinforce polymer (FRP) composite on low-velocity impact test (LVI). The glass FRP composites were fabricated using vacuum-assisted resin transfer moulding process, which is capable of producing constant thickness with high volume fractions of composite laminates as compared to the traditional wet hand lay-up method. The physical and impact properties were determined according to the ASTM D7137 standards. It was found that, bi-axial glass FRP composite can afford the energy until 90J and without the post perforation occurred, which mean that from the LVI test, the architecture weave of bi-axial glass FRP composite was showed high performance as compared to the unidirectional glass FRP composite. Lastly, component failures such as resin cracking, fibre breakage, fractured knit, fibre buckling, and delamination were also highlighted in this paper.

Degassing and layers variation effect on composite processing by vacuum assisted resin transfer moulding

Vacuum assisted resin transfer molding (VARTM) is a fiber reinforced composite (FRC) making process in which resin is impregnated to fabric by application of vacuum. This process is also known as vacuum infusion process. The critical issue in VARTM process is void generation. Voids form due to variety of reasons, most of which can be avoided. Vacuum degassing is one of the solutions which will reduce air entrapped inside resin during impregnation. In this work six laminates from jute and polyester resin were prepared, three with degassing and three without degassing with variation in number of jute layers 5, 10 and 15 respectively. Microscopic examination and mechanical properties have been observed before and after degassing. It was observed that degassing improves mechanical properties of composite laminates and reduce void content. It was observed that the thickness variation in laminate increased as number of layer increased.

Development of fiber-reinforced transparent composites

In this study, a continuous glass fiber-reinforced composite is manufactured using the vacuum assisted resin transfer molding (VARTM) process. The composite is manufactured from an S-glass fiber acting as reinforcement and an epoxy resin as matrix. Unlike a traditional E-glass fiber reinforcement, S-glass fibers give higher stiffness and provide easier manufacturability due to the value of the refractive index of S-glass lying within the range of refractive indices of the epoxy resin. The epoxy resin is synthesized Epon 826, Epalloy 5200, and hexahydropthalic anhydride and tailored to match refractive indices of the S-glass fibers. After synthesis of the resin, composite panels are manufactured from the synthesized epoxy resin and S-glass fibers with a bi-directional [0°/90°] 8-harness satin weave. VARTM process was utilized to manufacture the composite panels. Composite panels are visually inspected for transparency, and tensile, flexural, and impact testing is performed. Mechanical tests showed consistent results for tensile modulus, tensile strength, flexural modulus, flexural strength, and impact damage resistance.

Improvement of impregnation quality on out-of-autoclave processed CFRP aircraft wing spar through resin flow simulation

Vacuum-assisted resin transfer molding (VaRTM) is becoming one of the most robust alternatives for autoclave processes. VaRTM, which applies the resin injection method in a vacuum environment, generally uses fiber reinforcement and a polymer matrix separately in the process. The VaRTM is mainly dominated by the characteristics of constituent materials, such as preform permeability and resin viscosity. Among them, process design with the arrangement of resin inlet/outlet locations is closely related to process defects, and inappropriate inlet/outlet layouts cause voids, etc, which has a decisive effect on quality degradation. Therefore, in this study, a highly curved and twisted spar structure was fabricated by the VaRTM, and both flow simulations using Programs for Applied Mechanics–Resin Transfer Molding software and experimental test parts built with three different inlet/outlet line conditions were performed and compared to predict and improve impregnation quality. There was good agreement between the simulation and built test specimen for the three cases that the shorter inlet and outlet length resulted in improved impregnation quality. It was verified that impregnation and inner quality could be improved through flow simulation analysis during the VaRTM process.

Review and Suggestion of Failure Theories in Voids Scenario for VARTM Processed Composite Materials.

Fiber-reinforced composite structures are used in different applications due to their excellent strength to weight ratio. Due to cost and tool handling issues in conventional manufacturing processes, like resin transfer molding (RTM) and autoclave, vacuum-assisted resin transfer molding (VARTM) is the best choice among industries. VARTM is highly productive and cheap. However, the VARTM process produces complex, lightweight, and bulky structures, suitable for mass and cost-effective production, but the presence of voids and fiber misalignment in the final processed composite influences its strength. Voids are the primary defects, and they cannot be eliminated completely, so a design without considering void defects will entail unreliability. Many conventional failure theories were used for composite design but did not consider the effect of voids defects, thus creating misleading failure characteristics. Due to voids, stress and strain uncertainty affects failure mechanisms, such as microcrack, delamination, and fracture. That’s why a proper selection and understanding of failure theories is necessary. This review discusses previous conventional failure theories followed by work considering the void’s effect. Based on the review, a few prominent theories were suggested to estimate composite strength in the void scenario because they consider the effect of the voids through crack density, crack, or void modeling. These suggested theories were based on damage mechanics (discrete damage mechanics), fracture mechanics (virtual crack closure technique), and micromechanics (representative volume element). The suggested theories are well-established in finite element modeling (FEM), representing an effective time and money-saving tool in design strategy, with better early estimation to enhance current design practices’ effectiveness for composites. This paper gives an insight into choosing the failure theories for composites in the presence of voids, which are present in higher percentages in mass production and less-costly processes (VARTM).

Carbon fiber permeability characterization using VARTM process

The vacuum assisted resin transfer moulding (VARTM) process is extensively used for the fabrication of composite parts. The different process parameters are involved during composite manufacturing in the VARTM process. In this paper, flat plates have been fabricated with different thickness from carbon fiber reinforced polymer (CFRP) and epoxy resin along with hardener using VARTM process. The total number of layers of CFRP composite has been considered as 4, 8, and 12 in the experimentation. The digital camera has been used to record images and the resin flow during mould filling process. The permeability has been calculated along the length of the component for each case based on Darcy’s law. The variation in the permeability along with the mould filling time and infusion area has been observed for each fabricated composite plates. The permeability is maximum at resin inlet and gradually decreases along with the length and found minimum at resin outlet position for all fabricated CFRP flat plates. The time taken for covering 67% of the infusion area is approximately equal to the last 33% area during the mould filling in the VARTM process.

Numerical investigation of VARTM process using finite volume method

VARTM (Vacuum Assisted Resin Transfer Molding) is considered as a superior and simple method with respect to the manufacturing of sound composite parts due to the low setting up cost and consistency of the product obtained. The primary objective of the work is to propose an efficient method of numerical modeling to simulate the VARTM process and to validate with the experimental results. In numerical modeling, a control volume of specified dimensions that take the place of mold cavity in the experimental setup is defined, and the bi-directional E-glass fiber preform is assumed to be a porous structure. The experimentally obtained permeability value for different compaction pressures considered is given as an input to the numerical analysis and the completion time of the process is forecasted. For 1-Dimensional flow development, the proposed VARTM numerical simulation can be applied to mold cavities of complex geometries and the process completion time can thus be assured before the gelation time of the mixture.

An Experimental and Numerical Determination on Low-Velocity Impact Response of Hybrid Composite Laminate

In this study, experimental and numerical investigations were carried out in order to determine the mechanical properties and impact response of hybrid composite laminate. The hybrid composite laminate was formed from plain woven carbon fiber reinforced epoxy (CFRE) and plain woven glass fiber reinforced epoxy (GFRE) fiber using VARTM (vacuum-assisted resin transfer molding) process. The mechanical properties of the hybrid composites were determined using tensile test device with a 1 mm/min loading rate at room temperature. In addition, hybrid composites were subjected to low-velocity impact test under different impact energy levels (10, 20, 30, 40 J) for determining the impact response. Moreover, mechanical properties and impact responses of CFRE and GFRE laminates were also determined to compare to those of hybrid composite (HCGFRE). Microstructure analysis was performed to investigate the damage surfaces of the fiber and matrix in the composite material subjected to impact and tensile forces. In numerical analyses, composite damage model (Mat 54) was utilized in LS-DYNA® explicit finite element program to simulate the impact behavior of CFRE, GFRE and HCGFRE laminates. Consequently, the tensile test results showed that hybrid composite laminate behaved more ductile than carbon composite laminate and it exhibited more brittle behavior than glass composite laminate. Also, it was determined that absorbed energy and impact load capacity of HCGFRE composite laminate are between absorbed energy and impact load capacity of CFRE and GFRE composite laminate. It was determined that numerical results indicate a similar tendency with the experimental results.

Effects of plasma treatment on properties of carbon fiber and its reinforced resin composites

The influence of plasma treatment on the wettability of carbon fiber was studied using the vacuum assisted resin transfer molding (VARTM) process. The influence of plasma treatment on the mechanical properties of carbon fiber-reinforced polymer (CFRP) composites, including interlaminar shear strength and tensile properties, were investigated. The carbon fiber surface chemistry analysis was carried out by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Results showed that low-temperature plasma treatment had little effect on the surface morphology of the carbon fiber; however, it changed the chemical surface state of the carbon fiber, which contributed to enhance the wettability of the carbon fiber by increasing the perfusion speed of the resin to be more than two times of the original speed. The fiber wettability improvements are of great significance to the preparation of the CFRP composite by the VARTM process. Compared to untreated carbon fiber, the plasma treatment caused an acceptable decrease in tensile properties and offered an increase in the interlaminar shear strength of the CFRP composite. Low-temperature plasma treatment played an important role in the effective preparation and application of the CFRP composite.

Relaxation-Compression Resin Transfer Molding under Magnetic Field

Relaxation-compression resin transfer molding under magnetic field is a new variant of VARTM (“vacuum assisted resin transfer molding”) process, which uses a flexible magnetic membrane controlled by a magnetic force, in order to govern the relaxation and compression phases by changing the permeability of the fabric preform. Thus permits to the resin to enter easily into the mold and to increase the resin impregnation velocity and the fiber volume fraction. This innovation is based on the application of the TRIZ theory (“the theory of inventive problem solving”), which allows us to answer to the shortcomings and the conflict links exist inside the VARTM processes. The objective of this paper is to present this new process and to study the effect of the current intensity and the separated gap between the flexible magnetic membrane and solenoid on the permeability of the preform.

Flow modeling and simulation study of vacuum assisted resin transfer molding (VARTM) process: A review

In recent times, vacuum-assisted resin transfer molding (VARTM) has become a promising technique for the processing of large composite structures. On the contrary, there are few issues related to VARTM processing as many process parameters are involved and required to optimize them to achieve high fiber volume fraction containing composite material. These issues can be addressed and resolved by an understanding of various flow modeling techniques and simulation methods. In this present study, a review of different approaches in flow modeling and simulation of the VARTM process is presented. The processing technology of VARTM along with the fundamental and constitutive models for mold filling stage as well as curing stage such as permeability, compaction, resin viscosity and cure kinetics are presented. The numerical simulation methods adopted by various researchers used to simulate the filling processes with their specific applications and simulation software are also reported and reviewed. As an outcome, identification of permeability of various fibers and simulation processing time are more predominant factors to perform accurate VARTM simulation.

Real-Time and <i>In Situ</i> Monitoring of FRP by Rayleigh Scattering-Based Distributed Sensing

In-situ monitoring method of FRP (Fiber Reinforced Plastics) by built-in sensors is a key technology for developing future and high-reliable composite structures. The Rayleigh scattering-based distributed optical fiber sensor has high spatial resolution of 1mm and good embeddability into FRP and then it can be considered that the sensor is very suitable to in-situ monitoring of FRP. In the present paper, process monitoring and damage identification of FRP were conducted. In the process monitoring, flow-front of silicon oil impregnating into glass textile during VaRTM (Vacuum-assisted Resin Transfer Molding) process was measured. Comparing to visual observation results, it appeared that the maximum slope position of strain distribution showed flow-front position. In the health monitoring, damage identification of cross-ply GFRP laminates with delamination by the attached distribution optical fiber sensors was carried on. From the results, it was found that the strain varied largely on the delaminated section and then the delamination was detectable from the surface strain distribution measured by the optical fiber sensor.

Experimental Study of Thickness Gradient and Flow Simulation in VARTM Process

Vacuum assisted resin transfer moulding (VARTM) process is widely used for manufacturing composite products. It is very difficult to manufacture a composite component with small dimension tolerance using VARTM process. In this research paper, carbon fiber reinforced polymer (CFRP) flat plates have been manufactured using the VARTM process with a different combination of process parameters. The carbon fiber laminates with different thickness have been manufactured using the VARTM process. The thickness of manufactured components has been measured at different locations using non-contact type 3D scanning techniques. The warpage has been determined for each manufactured components. The compaction pressure has been measured using pressure gauge at a different location during manufacturing. The thickness variation, pressure variation and volume fraction have been determined across the length for each manufactured components for different thickness laminates. The mould filling time has been calculated using the numerical approach in ANSYS Fluent software and the same has been compared with experimental results. The percentage difference between the experimental and numerical approach has been found within 5 %.

Effect of permeability on GFRP laminate produced by VARTM process

Vacuum assisted resin transfer molding (VARTM) is one of the manufacturing technique that is viable for production of fiber reinforced polymer composite components suitable for aerospace, marine and commercial applications. However the repeatable quality of the product can be achieved by critically fixing the process parameters such as Vacuum Pressure (VP) and permeability of the preform. The present investigation is aimed at studying the effect of permeability for production of Glass Fiber Reinforced Polyester (GFRP) components with consistent quality. The VARTM mould is made with an acrylic transparent top cover to observe and record the resin flow pattern. Six layers of randomly placed glass fiber under five different vacuum pressures VP1 = 0.013, VP2 = 0.026, VP3 = 0.039, VP4 = 0.053 and VP5 = 0.066 MPa were studied. The laminates produced by this process under the above mentioned conditions were characterized with ASTM D procedures so as to study the effect of these process parameters on the quality of the laminate. And as mentioned there is a considerable effect of permeability on the impact strength and the void content in the laminates under different vacuum pressures. SEM analysis of the impact tested fractured GFRP composites showed the bonding of fiber and matrix.

Experimental and numerical investigation of compressive mechanical behaviour on woven carbon-Kevlar hybrid composites

Advanced polymer textile composites are characterised with high strength to weight ratio and tailored mechanical properties claiming their applications in advanced engineering sectors. The research work presented is focused on the development and characterisation of compressive behaviour of monolithic Kevlar and carbon-Kevlar hybrid fabric reinforced polymer composites (FRPCs). Vacuum-assisted resin transfer moulding process is used to cast the composite laminates. Results obtained present the effect of hybridisation of carbon yarns with Kevlar fabric, also compare the compression modulus and compressive strength of two fabrics along longitudinal axes. Fabrics with different weaving patterns, namely plain and twill are considered for reinforcement to experimentally investigate the role of weaving pattern plays in governing the mechanical strength of textile composite. FE model is generated to numerically simulate the compression loading behaviour of composites. Simulation results of longitudinal compression of carbon-Kevlar hybrid fabric composite show a good agreement with experimental results.

Modeling and Experimental Validation of the VARTM Process for Thin-Walled Preforms.

In this paper, recent shell model is advanced towards the calibration and validation of the Vacuum-assisted Resin Transfer Molding (VARTM) process in a novel way. The model solves the nonlinear and strongly coupled resin flow and preform deformation when the 3-D flow and stress problem is simplified to a corresponding 2-D problem. In this way, the computational efficiency is enhanced dramatically, which allows for simulations of the VARTM process of large scale thin-walled structures. The main novelty is that the assumptions of the neglected through-thickness flow and the restricted preform deformation along the normal of preform surface suffice well for the thin-walled VARTM process. The model shows excellent agreement with the VARTM process experiment. With good accuracy and high computational efficiency, the shell model provides an insight into the simulation-based optimization of the VARTM process. It can be applied to either determine locations of the gate and vents or optimize process parameters to reduce the deformation.

Mechanical and thermal behavior of hybrid glass/jute fiber reinforced composites with epoxy/polyester resin

The hybrid glass/jute fiber composites were fabricated by hand layup (HL) and vacuum assisted resin transfer molding (VARTM) method using epoxy and isophthalic polyester resins as matrices. The effects of fiber and matrix type as well as fabrication method on the tensile and flexural mechanical strength of resulting composites were investigated. The morphological fracture was analyzed based on scanning electron microscopy (SEM) images. Also, the curing characteristics of two matrix resins was studied by using differential scanning calorimetry (DSC). For glass fiber composite, the curing rate of polyester resin is faster at 100 °C than that of composite with epoxy matrix. Using VARTM process, the composite with high fiber volume fraction (Vf) of 52% was obtained.

Bending Properties of Zigzag-Shaped 3D Woven Spacer Composites: Experiment and FEM Simulation

Conventionally laminated spacer composites are extensively applied in many fields owing to their light weight. However, their impact resistance, interlaminar strength, and integrity are poor. In order to overcome these flaws, the zigzag-shaped 3D woven spacer composites were rationally designed. The zigzag-shaped 3D woven spacer fabrics with the basalt fiber filaments tows 400 tex (metric count of yarn) used as warp and weft yarns were fabricated on a common loom with low-cost processing. The zigzag-shaped 3D woven spacer composites were obtained using the VARTM (vacuum-assisted resin transfer molding) process. The three-point bending deformation and effects of damage in zigzag-shaped 3D woven spacer composites were studied both in experiment and using the finite element method (FEM). The bending properties of zigzag-shaped 3D woven spacer composites with different direction, different numbers of weaving cycle, and different heights were tested in experiments. In FEM simulation, the geometrical model was established to analyze the deformation and damage based on the 3D woven composite structure. Compared with data obtained from the experiments and FEM simulation, the results show good agreement and also prove the validity of the model. Based on the FEM results, the deformation, damage, and propagation of stress obtained from the model are very helpful in analyzing the failure mechanism of zigzag-shaped 3D woven composites. Furthermore, the results can significantly guide the fabrication process of real composite materials.