Resin Transfer Molding Research Articles

A Methodology to Reduce Thermal Gradients Due to the Exothermic Reactions in Resin Transfer Molding Applications

Resin transfer molding (RTM) is among the most used manufacturing processes for composite parts. Initially, the resin cure is initiated by heat supply to the mold. The supplementary heat generated during the reaction can cause thermal gradients in the composite, potentially leading to undesired residual stresses which can cause shrinkage and warpage. In the present numerical study of these processes, a one-dimensional finite difference method is used to predict the temperature evolution and the degree of cure in the course of the resin polymerization; the effect of some parameters on the thermal gradient is then analyzed, namely: the fiber nature, the use of multiple layers of reinforcement with different thermal properties and also the temperature cycle variation. The validity of this numerical model is tested by comparison with experimental and numerical results in the existing literature.

Nuevos Métodos De Fabricación Basadas En Estructuras Sándwich Para Su Aplicación En Carrocerías

The transport sector has exerted and continue to be the driving force for the development of new materials and lightweigth solutions. The present study focuses on the work developed in a recently completed European project (CARBODIN https://carbodin.eu/) where one of the main objectives is to develop innovative and affordable solutions for advanced car body shells. Composite materials appear to be one of the most promising candidates to attain these ambitious targets. However, to overcome the cost barrier as well as meet additional railway requirements, new strategies such as process integration and novel manufacturing routes are needed, which will offer a cost-effective industrial solution. The case study corresponds to a C-Groove insert used as an anchoring point to hang passenger seats off the car body side walls, to fix Interior Panels or luggage racks. To improve this design, a trendsetting design was developed to integrate composite C-Grooves to Composite sidewalls. This work will display the details of such design as well as the optimal manufacturing strategy to achieve it. An out of autoclave (OoA) manufacturing process was assisted through different monitoring technologies such as resin arrival sensors and thermography to ensure high quality components. Additionally, a multi-material approach based on 3D printed technologies has been tackled. A thorough analysis of the joint has been performed and different integration approaches have been explored by designing co-cured and co-bonded manufacturing stages. Finally, several demonstrators have been made and tested to define the most promising integration approach and scaling up yet again to a larger demonstrator.

The effect of stacking sequence and fiber orientation on tensile and flexural strength of fiber reinforced composite fabricated by VARTM process

In this study, Carbon, Glass, and Aramid fiber reinforced composite and their hybridized forms were fabricated using five different stacking sequences of the fabrics. Using the Vacuum Assisted Resin Transfer Molding (VARTM) procedure, epoxy resin was injected into these fabrics and allowed to cure at room temperature. From these five stacking sequences, a standard specimen with four different orientations viz. 0/90°, 15/75°, 30/60°, 45/-45° orientations were obtained using the Abrasive Water Jet Machining(AWJM) Process. The influence of stacking order and fiber orientation on tensile and flexural properties of composite was investigated. From the result of tensile testing, the highest and lowest tensile strength values were observed for neat carbon fiber reinforced composite at 0/90° orientation and at 45/-45° orientation respectively. The highest flexural strength was achieved in a hybrid combination of two layers of carbon, glass and aramid fabric for 0/90° whereas the lowest flexural strength was found in glass reinforced composite for the 45/-45° orientation.

Ultrasonic Monitoring of Resin Impregnation and Curing Processes in Vacuum Assisted Resin Transfer Molding

Ultrasonic Monitoring of Resin Impregnation and Curing Processes in Vacuum Assisted Resin Transfer Molding

Manufacturing of near-net-shape composite parts using Tailored Fiber Placement preforms

This paper demonstrates the feasibility of manufacturing a light and low cost near-net-shape vertebra from Tailored Fiber Placement (TFP) preforms. The TFP preforms were produced flat and sewn together at the ends by a classic sewing process. Low pressure Vacuum Assisted Resin Transfer Molding (VARTM) was used for the consolidation and impregnation of the preforms. The molding strategy was oriented towards the use of silicone conformers to ensure a compaction that well fits the preform despite its imperfections. The resulting part required a light finishing. The mass was reduced by 40% and the manufacturing cost by 76% compared to the original part.

Experimental investigation on mechanical and thermal characteristics of waste sheep wool fiber-filled epoxy composites

With the escalating trends of environmental contamination, the necessity of exploring environment friendly composites has increased. Foreseeing a sustainable future, this study investigates mechanical and thermal characteristics of woven (W), and non– woven waste sheep wool fiber (N, C, F) reinforced epoxy composites. The composites are fabricated using the in-house Vacuum Assisted Resin Transfer Molding (VARTM) technique in a controlled environment. Using animal fiber-filled epoxy composites were created. The density, void content, hardness, and tensile strength of differentially ordered waste sheep wool fiber have been examined. Also, thermal characteristics such as effective thermal conductivity (Keff) and glass transition temperature (Tg) of the said composites have been evaluated. The results of the experimental investigation reveal that non-woven needle punched (N) animal fiber polymer composites exhibit good interfacial adhesion between fiber and matrix with lower void content and higher tensile strength. Also, waste animal fiber-woven (W) and felt (F) polymer composites exhibit better hardness and low thermal conductivity. Thus, it can be said that the fabricated waste sheep wool fiber-filled epoxy composites exhibit better mechanical and thermal characteristics for insulating building components.

High temperature phenylethynyl-terminated imide oligomers derived from asymmetric diphenyl ether diamines for resin transfer molding

Resin transfer molding (RTM) require phenylethynyl-terminated imide oligomers (PETIs) to exhibit low melt temperatures and better melt stability. To decrease the melt temperatures of PETIs and improve their resin transfer moldable processability, asymmetric 4,4′-diaminodiphenyl ether substituted by fluorine (F-ODA), trifluoromethyl group (3F-ODA) or phenyl group (p-ODA) were introduced. Asymmetric molecular structure and substituent groups decrease the melt temperatures of PETIs, endowing PETIs with the wider processing temperature windows and low minimum melt viscosity (<1 Pa s). These polyimides show pot lives of 30–60 min at 260–280 °C. Furthermore, the effects of backbone structure on melt fluidity of imide oligomers were discussed by the calculation of viscous activation energy (Ea,η) and analysis of Molecular Dynamics. PETI-3F and PETI-P based on 3F-ODA and p-ODA exhibit low and stable melt viscosities (<1 Pa s) at 250–270 °C and 260–270 °C for 4 h respectively, enabling the successful fabrication of carbon fiber reinforced polyimide composites via RTM process. After cured at 380 °C, the thermosets of PETI-3 and PETI-4 show high Tg of 412 °C and 402 °C and good thermal stability (Td5>550 °C). Cured PETI-3 and PETI-4 also show good mechanical properties (tensile strength >50 MPa). In comparison with p-ODA, 3F-ODA could provide PETIs with superior resin transfer moldable processability and higher heat-resistance and is more suitable to synthesize PETIs for RTM application, because of better balance between polymer segmental mobility and polymer chain packing.

Study on Curing Deformation of Composite Thin Shells Prepared by M-CRTM with Adjustable Injection Gap.

A composite thin shell with a high fiber volume fraction prepared by resin transfer molding (RTM) may have void defects, which create deformations in the final curing and lead to the final product being unable to meet the actual assembly requirements. Taking a helmet shell as an example, a multi-directional compression RTM (M-CRTM) method with an adjustable injection gap is proposed according to the shape of the thin shell. This method can increase the injection gap to reduce the fiber volume fraction during the injection process, making it easier for the resin to penetrate the reinforcement and for air bubbles to exit the mold. X-ray CT detection shows that the porosity of the helmet shell prepared by the newly developed technology is 36.6% lower than that of the RTM-molded sample. The void's distribution is more uniform, and its size is decreased, as is the number of voids, especially large voids. The results show that the maximum curing deformation of the M-CRTM-molded helmet shell is reduced by 13.7% compared to the RTM molded sample. This paper then further studies the deformation types of the shell and analyzes the causes of such results, which plays an important role in promoting the application of composite thin shells.

Application of capacitive sensors and controlled injection pressure to minimize void formation in resin transfer molding

AbstractVoid formation as a result of irregular resin flow at the flow front is discussed and a practical method for reducing void formation during resin transfer molding (RTM) is introduced. In this study, a sensor system is developed for in situ measurement of resin velocity inside a closed cavity. Assisted by the acquired data, a resin injection system is augmented to automatically adjust the injection pressure and achieve a uniform flow front velocity. It is proven, that the developed system is suited to monitor the resin flow front and is able to sufficiently control flow velocity of a linear flow front. Test specimen produced by this method show significantly reduced void contents in comparison to a common resin transfer molding process.

Towards the development of a fire retardant sugar-cane bagasse ply for composite manufacture: A flammability study

This study investigated suspending two fire retardants in sugar-cane bagasse plies used for manufacturing natural fibre reinforced composites. Sugar-cane bagasse was alkali treated, blended with either APP (Ammonium Polyphosphate) or ATH (Aluminium Hydroxide), pressed and dried to form plies. Composites were manufactured using a light resin transfer moulding process with epoxy resin. Composites manufactured with fire retardant suspended plies were compared to composites with plies layered with equivalent amounts of fire retardants. The composites were characterised using thermogravimetric analysis (TGA) for thermal stability and char yield, isotropic hot disc method for thermal properties, and cone calorimeter for studying ignition and flammability. Plies suspended with APP had the highest char yield of 58% (in nitrogen), reducing to 26% in the composite form, with degradation driven by the epoxy matrix. The composite layered with ATH had the latest ignition times of 118 s when tested with a radiant heat flux of 35 kW/m2. The composite layered with APP displayed the lowest average heat release rate (179.7k W/m2), peak heat release rate (305.6k W/m2), and total heat released (135.5 MJ/kg). When assessing the fire growth, the composite layered with APP was again favourable. While the layering yielded more favourable results than the suspension of the same retardants, this study showed that a rudimentary process was able to suspend enough retardants to improve the behaviour of the resulting composites in a fire scenario.

Numerical modeling of suspension impregnation through a fibrous medium: Application to the CRTM process

In this article, a numerical model dedicated to the impregnation modeling of a fibrous medium by a particle-filled resin (suspension) is proposed. It allows to simulate and analyze the mold filling with a particle-filled resin during the Compression Resin Transfer Molding (CRTM) process at a given compression speed and compaction force. As per our knowledge, no such work with this last compression mode has already been reported in the literature. The simulation results of our approach were compared with the analytical as well as experimental results, and found in agreement. With an objective to analyze the effect of the process parameters on the suspension flow, particularly on the final distribution of the particles in the developed composite, a detailed parametric study was done. Finally, a comparison between the injection and compression modes is conducted and discussed. The obtained results demonstrate that the particle volume per mold cavity volume depends on the initial concentration, the distance traveled, and the initial volume fraction of the fiber, while it is independent of parameters values of injection and compression. It was also observed that the imposed pressure injection and the imposed force compression are the most favorable to produce composite parts using CRTM.

Thermo-mechanical properties of RTM-made carbon fibre/polyimide composite attaching collar under transient heating

This study focuses on the thermo-mechanical properties of Carbon Fibre/Polyimide Composite (CFPC) attaching collars under transient heating. The CFPC attaching collars were fabricated by a high-temperature resin transfer moulding process, and their thermo-mechanical properties under the conditions of simultaneous transient heating and bending load were investigated. The results show that the attaching collar tends to fail at 118% of the limit load. The failure mode includes the fracture of the connecting screws, local extrusion damage of the hole edges, and slight ablation damage at the outer plies. And there is no observable residual deformation in the composite attaching collar. Furthermore, considering that the material properties vary with temperature, a progressive damage model based on the sequential thermo-mechanical coupling method was established to study the failure mechanism of the attaching collar. Finally, the damage factor of the CFPC was calculated to assess the safety status of the attaching collar. The results show that the primary damage modes of the composite attaching collar are intralaminar failure, which mainly occurs at the heat insulation layer and the hole edges, and these slightly affect the structural bearing capacity. A good correlation between the experiment and FEA is obtained. The test methods and analysis models proposed contribute to the safety assessment of composite structures under transient heating.

On the Resin Transfer Molding (RTM) Infiltration of Fiber-Reinforced Composites Made by Tailored Fiber Placement.

Tailored fiber placement (TFP) is a preform manufacturing process in which rovings made of fibrous material are stitched onto a base material, increasing the freedom for the placement of fibers. Due to the particular kinematics of the process, the infiltration of TFP preforms with resin transfer molding (RTM) is sensitive to multiple processes and material parameters, such as injection pressure, resin viscosity, and fiber architecture. An experimental study is conducted to investigate the influence of TFP manufacturing parameters on the infiltration process. A transparent RTM tool that enables visual tracking of the resin flow front was developed and constructed. Microsection evaluations were produced to observe the thickness of each part of the composite and evaluate the fiber volume content of that part. Qualitative results have shown that the infiltration process in TFP structures is strongly influenced by a top and bottom flow layer. The stitching points and the yarn also create channels for the resin to flow. Furthermore, the stitching creates some eye-like regions, which are resin-rich zones and are normally not taken into account during the infusion of TFP parts.

Fatigue behavior of self-healing glass fiber/epoxy composites with addition of poly (ethylene-co-methacrylic acid) (EMAA)

The interest in repair technologies for polymer composites has increased significantly over the last decades, due to the growing use of these materials in structural applications. In this study, poly (ethylene-co-methacrylic acid) (EMAA) was used as self-healing agent to glass fiber/epoxy composite. Materials with EMAA contents of 2 wt% and 5 wt% were manufactured using Resin Transfer Molding (RTM) and the effects of the healing agent on the properties were investigated using tensile tests and Dynamic Mechanical Analysis (DMA). Results show slight variation of properties, which was more pronounced as the content of EMAA increased. In addition, the healing efficiency was investigated through fatigue tests and the addition of higher content of EMAA increased the number of cycles to failure after the healing activation cycle.

Investigating the moisture absorption behavior of bamboo fiber-reinforced epoxy composites by modelling

The aim of this research was to investigate the moisture absorption of bamboo fibers (BFs) and their composites manufactured using different methods. The hygroscopic properties of BFs, jute fibers (JFs), glass fibers (GFs), and epoxy (EP) were compared and analyzed using dynamic vapor sorption (DVS), as well as the hygroscopic properties of the BF-Naval Ordnance Laboratory (BF-NOL), JF-NOL, GF-NOL, and bamboo fiber-reinforced epoxy composites manufactured via filament winding (FW), hot pressing (HP), and resin transfer molding (RTM). The results were analyzed using the Guggenheim-Anderson-deBoer (GAB), parallel exponential kinetics (PEK), and DoseResp models. The results indicated that BFs conformed to type II. The moisture adsorption isotherms of BF-NOL, JF-NOL, GF-NOL, and BF composites prepared by different molding processes exhibited a typical V-shape. The GAB and DoseResp models provided good fits to the changes in adsorption and desorption processes. The final equilibrium moisture content (EMC) of BFs and BF-NOL were 27.1% and 3.95%, respectively, the final EMC of BF composites prepared by RTM was 2.34%.

Influence of hygrothermal ageing on the novel infusible thermoplastic resin reinforced with quadriaxial non-crimp glass fabrics

Elium® is a novel liquid Methylmethacrylate thermoplastic (TP) matrix that can be cured at room temperature. Elium® resin provides the properties of TP polymer composites and is a competitive alternative to epoxy-based composites. In this work, a quadriaxial non-crimp (NC) glass fabric/Elium® based polymer composites were manufactured using vacuum assisted resin transfer moulding (VaRTM). The static mechanical properties of these composites were evaluated under the tensile and flexural loads. Further, interfacial properties like interlaminar shear strength (ILSS) and fracture toughness (Mode-I and Mode-II) were characterised. To study the influence of ageing on the mechanical properties of glass fabric/Elium® (GF/E) based composites, the test samples were aged in distilled water at a temperature of 60°C for 60 days. The obtained mechanical properties were compared between dry samples (control) and post-water immersed (aged) samples. It was found that water ageing degraded the properties of tensile, flexural strength, ILSS and Mode-II toughness by 30%, 59%, 46%, 37%, respectively. On the contrary, Mode-I fracture toughness of aged samples was 90% higher, indicating significant fibre bridging due to ageing. The microscopy and scanning electron microscopy (SEM) revealed significant failure as the degradation of fibre/matrix interface due to hygrothermal ageing. The overall performance of GF/E composites with infusible TP resin is sensitive to hygrothermal ageing.

Physical-Mechanical Properties of Bamboo-Textile-Reinforced Polymer Made with Vacuum-Assist Resin Transfer Molding

ABSTRACT Bamboo fiber-reinforced polymers have been widely studied as natural fiber composites. This study fabricated a continuous bamboo-textile-reinforced polymer (BTRP) composite by using woven bamboo strips and epoxy through vacuum-assisted resin transfer molding (VA-RTM). The physical properties, including bulk density and equilibrium moisture content, of various BTRP specimens with different textile architectures, stacking sequences, loading axes, and numbers of layers were preliminarily evaluated. The specimens’ flexural properties, including strength, modulus, integral load – deflection relationship, damage parameters, and fractography characteristics, were also examined. As the number of layers increased, the flexural strength decreased but modulus values increased. When the number of layers was constant, the plain-woven BTRP specimens had slightly higher strength and modulus values than did the twill-woven specimens. The BTRP specimens exhibited remarkable mechanical properties and staged failure behaviors unique to laminated materials. Moreover, the stiffness of the specimens was attenuated before reaching the ultimate load, which was attributed to microscopic interphase damage, and the various architectures affected the specimens’ fracture modes. The gradual multistage failure modes of the specimens imply that the fabricated composite is relatively safe for use. According to these results, the fabricated composite incorporates the advantages of VA-RTM and continuous nontwisted bamboo strips, indicating that it has substantial commercial potential.

Development of a Novel Biobased Polyurethane Resin System for Structural Composites

Polyurethanes are gaining increasing interest for their use as structural components subjected to cyclic loads, such as leaf springs. Thermoset polyurethane (PUR) based technology offers some advantages, such as fatigue resistance, low viscosity, and fast curing. However, current PUR formulations present two major drawbacks: their petrochemical origin and high reactivity. The aim of this work was to develop a novel biobased PUR (BIO-PUR) with the required mechanical properties and processability for manufacturing structural composites by resin transfer moulding (RTM). For this purpose, a high functionality and high hydroxyl index castor-oil-based polyol was used combined with a biobased glycerol (BIO-Gly) to increase the crosslinking density and improve the final properties of the BIO-PUR. The viscosity and reactivity of the different systems were studied by means of rheology tests and differential scanning calorimetry (DSC). Thermal and mechanical properties were studied by dynamic mechanical analysis (DMA) and flexural tests. Furthermore, the RTM process of a representative part was simulated and validated through the manufacturing and testing of plates. The properties of the BIO-PUR resin systems were strongly influenced by the addition of biobased glycerol and its effect on the crosslinking density. The combination of a high functionality and hydroxyl index biobased polyol with the biobased glycerol resulted in a high-performance BIO-PUR with the required reactivity and final properties for structural applications.

Fatigue life of thin pre-cracked aluminum alloy panel repaired with CFRP patch at elevated temperature

The fatigue life of a thin pre-cracked aluminum alloy panel, repaired with CFRP patches was investigated. Aluminum alloy 6061-T6 plate having a center crack (20 mm) was repaired by varying no. of CFRP patches made of several UD CFRP plies. Asymmetrically bonded CFRP patched specimen were prepared using VARTM (Vacuum Assisted Resin Transfer Moulding). Different configurations of CFRP plies were tested with changes in stiffness ratio and environment temperature mainly at 80°C and room temperature. Using a computerized axial fatigue test machine the specimens were loaded under tension – tension fatigue load. Fatigue testing was carried out at 50% of yield strength of skin made of Al 6061-T6 alloy. Frequency of 9 Hz and Stress ratio, R = 0.1 were maintained throughout the experimentation. A set of three specimens under each temperature condition and patch configuration were tested and results were recorded. Fatigue crack propagation cycles till final failure, Nf of the specimen was monitored. The numerical simulations were carried out to find SIF at various crack lengths. The results were compared with experimental results. The tested specimens at elevated temperature showed an increase in fatigue cycles compared to room temperature specimens.

Effect of Mat Fiber Lay-up and Resin Transfer Molding Process on Flexural and Tensile Properties of Luffa Mat Reinforced Composites

ABSTRACT In this paper, two different parts of fiber orientation in the structure of luffa mat, quasi-unidirectional (Part A) and random (Part B), were examined in tensile test. Flexural and tensile tests were conducted on composites reinforced with luffa fiber mat produced by a resin transfer molding (RTM) process. Additionally, the effect of the superposition of the luffa mat, as well as the method of manufacturing on the improvement of the mechanical properties of composites, was studied. Obtained results have shown that the tensile mechanical properties of the luffa mat show Young’s modulus and the tensile strength are higher where the fibers are in the quasi-unidirectional direction (Part A) and strain at break is higher where the fibers are randomly oriented (Part B). The steps followed for the preparation, the superposition of the luffa mat, and the method of manufacturing of the luffa/epoxy composites have shown better mechanical properties in tensile and flexural, with Young’s modulus values of 7.41 ± 0.42 and 6.79 ± 0.3 GPa and strengths of 67.77 ± 1.82 and 67.57 ± 4.29 MPa, respectively, compared to other luffa fiber-reinforced composites already cited in all literature.