High Pressure Resin Transfer Molding Research Articles

Fiber fracture behavior of high-pressure resin transfer molded (HP-RTM) carbon/epoxy multidirectional laminates under compression-compression fatigue loading

The influence of different stress levels on the fatigue life and fracture behavior of laminated composites have been evaluated under compression-compression (C–C) loading conditions. Carbon/epoxy multidirectional (MD) laminate specimen was designed with eight layers [0°, ± 45°, 0°]s of unidirectional plies. The preforms were molded by a high-pressure resin transfer molding (HP-RTM) process. As part of the study, a static compression test was performed. The C–C fatigue loads were applied at −260 MPa, −280 MPa, −300 MPa, and −320 MP compression stress until failure or two million cycle loadings. The fatigue limit has been obtained at −265 MPa stress by stress-cycle number (S-N) curve analysis, which is 51.4 % of static compression strength. The damage behavior was identified after C–C fatigue tests. By using optical and scanning electron microscopy, fiber fracture, matrix cracking, and fiber/matrix interface debonding were observed. Under the C–C fatigue loading conditions, fiber fracture modes were characterized by rough cross-sections, shear, and line-shaped edges.

Tension-tension fatigue properties of multiaxial laminated carbon/epoxy composites molded by high-pressure resin transfer molding (HP-RTM) process

Engineering structures are often subjected to cyclic-loading conditions, which detrimentally affect the component’s service life and damage tolerance. The fatigue behavior of multiaxial laminated composites manufactured with unidirectional plies has been analyzed. Carbon/epoxy composite laminate was molded by a high-pressure resin transfer molding (HP-RTM) process. Specimens were subjected to tension-tension (T-T) fatigue stress of 65 %–75 % of static tensile strength until failure or up to one million cycles. An analysis of the maximum stress-cycle number (S-N) curve is conducted to determine the fatigue limits of the material. The predetermined fatigue limit has been obtained at 717.5 MPa stress, which is about 67 % of static tensile strength under tension-tension stress conditions. Fatigue failures under tension-tension loading conditions are associated with fiber breakage, fiber pull-out, and plies delamination. This research aimed to understand the fatigue behavior and fracture mechanism of multiaxial laminated composites under tension-tension cyclic loading conditions and collect more data for future research.

Automated Process Based on Functionalized Preform and Net-shape High Performance Resin Transfer Molding for High Volume Structural Applications

In this paper, a new process is highlighted for mass production of composite structural parts for the automotive and high-volume aerospace markets. This process follows different steps: (1) Simulation of the process to optimize the design of the 3D part and its corresponding 2D blank, (2) High speed Automated Fiber Placement (AFP) of 2D tailored dry preform blanks made from direct fiber, online fiber spreading and binder application, (3) Preform functionalization to improve its formability and permeability, but also to make handling and trimming easier, (4) Forming of the 2D functionalized preform to 3D shape and net shape trimming, (5) Net shape preform impregnation with High-Pressure-Resin-Transfer-Molding (HP-RTM), thanks to excellent through thickness (z direction) permeability, and preform stability. To assess the process performance and resulting parts, 3D parts and 2D coupons were manufactured using the new developed preforms and Non-Crimp-Fabric (NCF), having in both cases the same fiber and matrix. The performances were evaluated all along the process steps and the results show improvements in several key process parameters, equivalent mechanical performances and increase surface quality, hence resulting in less effort for surface preparation.

Flow Front Monitoring in High-Pressure Resin Transfer Molding Using Phased Array Ultrasonic Testing to Optimize Mold Filling Simulations.

During the production of fiber-reinforced plastics using resin transfer molding (RTM), various characteristic defects and flaws can occur, such as fiber displacement and fiber waviness. Particularly in high-pressure RTM (HP-RTM), fiber misalignments are generated during infiltration by local peaks in the flow rate, leading to a significant reduction in the mechanical properties. To minimize or avoid this effect, the manufacturing process must be well controlled. Simulative approaches allow for a basic design of the mold filling process; however, due to the high number of influencing variables, the real behavior cannot be exactly reproduced. The focus of this work is on flow front monitoring in an HP-RTM mold using phased array ultrasonic testing. By using an established non-destructive testing instrument, the effort required for integration into the manufacturing process can be significantly reduced. For this purpose, investigations were carried out during the production of test specimens composed of glass fiber-reinforced polyurethane resin. Specifically, a phased array ultrasonic probe was used to record individual line scans over the form filling time. Taking into account the specifications of the probe used in these experiments, an area of 48.45 mm was inspected with a spatial resolution of 0.85 mm derived from the pitch. Due to the aperture that had to be applied to improve the signal-to-noise ratio, an averaging of the measured values similar to a moving average over a window of 6.8 mm had to be considered. By varying the orientation of the phased array probe and therefore the orientation of the line scans, it is possible to determine the local flow velocities of the matrix system during mold filling. Furthermore, process simulation studies with locally varying fiber volume contents were carried out. Despite the locally limited measuring range of the monitoring method presented, conclusions about the global flow behavior in a large mold can be drawn by comparing the experimentally determined results with the process simulation studies. The agreement between the measurement and simulation was thus improved by around 70%.

Data-physics driven multiscale approach for high-pressure resin transfer molding (HP-RTM)

We present a multiscale computational framework for high-pressure resin transfer molding of fiber-reinforced composites. Due to the relatively rapid speed of resin flow and the significant convective effects, this process is governed by the nonlinear steady-state Navier–Stokes equations, as opposed to the linear Stokes equations commonly adopted for the simulation of classical resin transfer molding processes. To overcome the computational challenge of directly solving the high-pressure resin filling problem through the fiber preform, we developed a data-driven nonlinear homogenization approach where the average velocity and instantaneous permeability computed from the microscale representative volume element problem provide solution-dependent coefficients for the macroscale problem. The proposed data-physics driven computational framework has been validated against the direct numerical solution of the steady-state Navier–Stokes equations.

Experimental Characterization and Numerical Simulation of Voids in CFRP Components Processed by HP-RTM.

The long cycle of manufacturing continuous carbon fiber-reinforced composite has significantly limited its application in mass vehicle production. High-pressure resin transfer molding (HP-RTM) is the process with the ability to manufacture composites in a relatively short forming cycle (<5 min) using fast reactive resin. The present study aims to investigate the influence of HP-RTM process variables including fiber volume fraction and resin injection flow rate on void characteristics, and flexural properties of manufactured CFRP components based on experiments and numerical simulations. An ultrasonic scanning system and optical microscope were selected to analyze defects, especially void characteristics. Quasi-static bending experiments were implemented for the CFRP specimens with different void contents to find their correlation with material’s flexural properties. The results showed that there was also a close correlation between void content and the flexural strength of manufactured laminates, as the flexural strength decreased by around 8% when the void content increased by ~0.5%. In most cases, the void size was smaller than 50 μm. The number of voids substantially increased with the increase in resin injection flow rate, while the potential effect of resin injection flow rate was far greater than the effect of fiber volume fraction on void contents. To form complicated CFRP components with better mechanical performance, resin injection flow rate should be carefully decided through simulations or preliminary experiments.

Investigation of a Non-Equilibrium Energy Model for Resin Transfer Molding Simulations

Due to the high design freedom and weight specific properties carbon fiber reinforced plastics (CFRP) offer significant potential in light-weighting applications, specifically in the automotive sector. The demand for medium to high production quantities with consistent material properties has paved the way for the use of high-pressure resin transfer molding (HP-RTM). Due to high experimental cost and number of the operational parameters the development of numerical simulations to predict part quality is growing. Despite this, erroneous assumptions and simplifications limit the application of HP-RTM models, specifically with regards to the energy models used to model the heat transfer occurring during infiltration. The current work investigates the operating parameters at which the thermal non-equilibrium energy model’s increased computational cost and complexity is worth added accuracy. It was found that in nearly all cases, using the thermal non-equilibrium is required to obtain an accurate prediction of the temperature development and resulting final properties within the mold after the infiltration process.

Phosphazene as an effective flame retardant for rapid curing epoxy resins

A rapid curing, low viscosity epoxy amine resin developed for high pressure resin transfer moulding composite fabrication possessing good thermal and mechanical properties and excellent flame retardancy after cure is presented here. The resin system consists of diglycidyl ether of bisphenol F (DGEBF), an epoxy phenolic novolac resin and diethyl toluene diamine (DETDA), while rapid cure is enabled by 2-ethyl-4-methylimidazole (2E4MI) catalysis. The fire-retardant additive, a crystalline powder, hexaphenoxy cyclotriphosphazene (HPCTP) produces only a small increase in viscosity and regardless of additive concentration, the formulations are less than 200 mPas at processing temperatures of between 80 and 125 °C. Using the UL-94 vertical burn test, a V0 rating and a limiting oxygen index (LOI) of 36.2% were achieved using only 10 phr HPCTP. Indeed at 20 phr of HPCTP an LOI of 43.6% was achieved. The HPCTP additive remains miscible in the network after cure which reduces reactivity modestly and the glass transition temperature (Tg), but the flexural properties, including modulus, strength and strain to failure, either increase modestly or were unaffected.

Study of flow-induced fiber in-plane deformation during high pressure resin transfer molding

High Pressure Resin Transfer Molding (HP-RTM) is a new variant of composite Resin Transfer Molding (RTM) process that enables a short cycle time and a high composite strength to weight ratio, thus presents a great potential for fabricating automotive structural parts. Due to the high injection pressure, fiber-tow washout is becoming one of the major defects which impact the properties of composite materials. To predict and mitigate the fiber-tow washout problem, approaches of both experimental process optimization and computational prediction are essential. In this paper, an experimental study of fiber-tow washout is undertaken to determine the flow injection limits beyond which the preform deformation can be observed at various fiber volume fractions. A feasibility map is developed for a specific fabric and resin combination. It provides a means to determine the injection rates and fiber volume fractions to fabricate a quality part with minimal in-plane fiber washout due to the hydrodynamically flow-induced force during the HP-RTM process.

Synthesis of a phosphorus‑silicone modifier imparting excellent flame retardancy and improved mechanical properties to a rapid cure epoxy

A liquid bi-functional phosphaphenanthrene siloxane molecule that imparts excellent flame-retardancy and improved mechanical properties to an epoxy amine network was identified and synthesized. The modifier was added to a reactive epoxy amine system to create a low viscosity, miscible, flame retardant resin potentially able to be manufactured via high-pressure resin transfer molding (HP-RTM). The additive reduced the viscosity of the epoxy resin system, remained miscible in the epoxy resin after cure producing a transparent network while simultaneously enhancing self-extinguishing flame retardancy, flexural properties and fracture toughness. At a concentration of 25%, the viscosity of the modified resin system prior to cure was very low (less than 100 mPa.s at 80 °C), cured rapidly (less than 8 min at 150 °C), exhibited a Tg over 110 °C, displayed improved flexural strength (13%), modulus (23%) and fracture toughness (23%), increased thermal stability and displayed self-extinguishing behaviour (UL 94 V-0). Examination after combustion revealed a transformation to a porous but stable char layer likely a result of the synergistic effects of the silicon and phosphorus. The results presented here using represent a promising development for next generation modified epoxy resin systems targeted towards rapid manufacturing of composite materials using HP-RTM.

Microwave absorption performance enhancement using glass fiber-reinforced polymer nanocomposites containing dielectric fillers in X-band

Microwave absorption properties of radar absorbing structures in X-band frequency have been investigated using carbon-based dielectric filler materials. These structures are composed of E-glass/epoxy laminates filled with various wt% (0–2.5 with an increment of 0.5) of graphene and multiwalled carbon nanotubes individually. Composite fabrication has been done using high-pressure resin transfer molding (HPRTM). The pertinent electromagnetic (EM) parameters of composite structures are measured using the waveguide measurement technique in X-band. From the results, a single-layered polymer composite with 2.5% graphene contains better absorption than others. Among multilayered structures, the 11-layered composite structure has shown the best absorption performance (reflection loss (RL) = −21 dB) which is equal to 99.9% of incident EM radiation absorption in X-band. It is found that the single-layered structure has shown ineffective absorption performance compared to the multilayered structure under low weight concentrations. Moreover, a mathematical model to predict RL of different combinations of multilayered structures based on EM wave theory is proposed for the calculation of optimum layer combination for minimizing time and money. The predictions of the mathematical model are validated for the 11-layered structure using experimentation.

Design and development of polymeric nanocomposite reinforced with graphene for effective EMI shielding in X-band

The effect of filler material concentration on Electromagnetic Interference (EMI) Shielding Effectiveness (SE) of polymeric nanocomposites has been studied. Computational model was developed for shielding performance of graphene polymeric nanocomposites. Nanocomposites were fabricated using High Pressure Resin Transfer Molding (HPRTM) method, latter EM shielding properties were measured experimentally using waveguide technique. It is observed that SE increases with increase in wt% of graphene. From the results, it is perceived that nanocomposite with 2.5 wt% of graphene shows good shielding with the range of −27 dB to −30 dB, doubled in comparison to pure polymeric composite. Numerical simulations of various graphene nanocomposites have been carried out for the prediction of SE while incorporating EM properties of corresponding nanocomposite as input. Excellent agreement between numerical simulations and experimental results has been observed. The developed numerical model predicts SE values of graphene nanocomposites in −30 dB range which certainly falls in the X-band.

Embedded Based Real-Time Monitoring in the High-Pressure Resin Transfer Molding Process for CFRP

Carbon Fiber Reinforced Plastics (CFRP) is a material developed for its high strength and light weight in a broad variety of industries including aerospace, automotive, and leisure. Due to the rapid molding cycle time, high-pressure resin transfer molding (HP-RTM) processes are prone to molding defects and susceptible to various process variables such as the resin injection rate, pressure and temperature in the mold, vacuum, end-gap, pressing force, and binder. In recent years, process monitoring technology with various sensors has been applied to stabilize the HP-RTM process and control process variables. The field-programmable gate array (FPGA) based embedded monitoring system proposed in this study enabled high-speed real-time signal processing with multiple sensors, namely pressure, temperature, and linear variable differential transformer (LVDT), and proved feasibility in the field. In the HP-RTM process, the impregnation and curing of the resin were predicted from the cavity pressure and temperature variations during the injection and curing stages. In addition, the thickness of the CFRP specimen was deduced from the change in the end-gap through the detection of the LVDT signal. Therefore, the causes of molding defects were analyzed through process monitoring and the influence of molding defects on the molding quality of CFRP was investigated.

Quasi-static and dynamic characterization of unidirectional non-crimp carbon fiber fabric composites processed by HP-RTM

Recently developed high-pressure resin transfer molding (HP-RTM) processes have enabled the integration of lightweight fiber-reinforced composites into automobiles (e.g., frame and roof components, floor segments), which may also be suitable for energy absorption applications such as front crush structures in high volume production vehicles. Heavy tow stitch-bonded non-crimp fabrics with rapid curing resins have been recently used to fabricate HP-RTM parts; however, there is a lack of mechanical property data in the literature for such materials. To fill this gap and support the development of lightweight automotive structures, this study reports an investigation assessing the microstructure, quasi-static and dynamic mechanical properties of a non-crimp carbon fabric composite manufactured by HP-RTM, as well as properties of the rapid curing neat epoxy resin. The presented study of the microstructure and constituent properties provide data for in-depth microstructural modeling of the processed non-crimp fabric HP-RTM composite. The study reports 18–20% increase in the tensile transverse strength and strain-at-failure at strain rates on the order of 1000 s−1. Measured macroscopic material properties can be used as input data for numerical modeling of automotive composite structures, including simulations of vehicle collisions.

Methods for process-related resin selection and optimisation in high-pressure resin transfer moulding

ABSTRACTA framework for process-related resin selection and optimisation is proposed in the context of research and development for industrial applications of high-pressure resin transfer moulding. The first stage involves validation of the reaction kinetics model by differential scanning calorimetry and characterisation of viscosity, storage- and viscous-shear moduli by dynamic mechanical analysis in a rheometer as a function of time. It also includes capillary pressure measurements of curing resin impregnating a fibre yarn. Process-related resin selection criteria are based on the optimisation of cycle time, including filling time against gel time, micro-infiltration time and demould time. The proposed framework and associated test and analysis methodologies are applied to three epoxy resin systems in connection with carbon fibre reinforcement.

Comparative life cycle assessment of low-pressure RTM, compression RTM and high-pressure RTM manufacturing processes to produce CFRP car hoods

Advanced composite materials, especially those based on carbon fibers, have been attracting the interest of industrial companies for producing light and high-performance components. Resin Transfer Molding (RTM) and its variants have been recognized as the most promising processes to manufacture CFRP (Carbon Fiber Reinforced Polymer) products in a cost-effective way. However, recent research studies highlighted environmental concerns regarding the use of CFRP parts due to the high environmental load related to their production. In this context, the main scope of the present paper is to investigate and compare the environmental impacts of three alternative manufacturing processes for producing CFRP car hoods: RTM, High-Pressure RTM and Compression-RTM. This analysis has been carried out through the standard Life Cycle Assessment methodology. The system boundaries include all the flows related to manufacturing of the hood and an end of life. Results calculated by using the ReCiPe mid-point/end-point method suggest that the eco-friendliest variant is the Compression-RTM.

Forming characteristics during the high-pressure resin transfer molding process for CFRP

The high-pressure resin transfer molding (HP-RTM) process has potential applicability to the mass production of lightweight vehicles made of carbon fiber-reinforced plastic in the automotive industry. In recent years, the development of robust equipment, new processes, and fast cure matrix systems have significantly reduced the cycle time to less than 5 min. In this study, the cavity pressure of the HP-RTM process was monitored to analyze the molding characteristics. The mold was equipped with two cavity pressure sensors and three temperature sensors. The cavity pressure characteristics during the HP-RTM injection, pressurization, and curing processes were studied. Selected process parameters such as the mold cap size, maximum pressing force, and injection volume were analyzed. The results demonstrated correlations between the selected process parameters and final forming characteristics.

A model for fibre washout during high injection pressure resin transfer moulding

High injection pressure resin transfer moulding is a variant of resin transfer moulding in which the preform is compressed in a tool and resin is injected into the mould under very high pressure. The high injection pressure (&gt;20 bar) introduces possible fibre washout that translates into manufacturing defects or causes inconsistencies in processing and leads to scatter in mechanical properties of composite parts. A model is presented which quantifies and provides insight into the influence of process variables such as clamping force and injection pressure on fibre washout distance (the one-dimensional model assumes a rigid preform). A generalised one-dimensional stress model for fibre washout is presented for regions that are impregnated with the resin and the regions that are dry. The model shows fibre washout to be significant at the beginning of the injection process. The model allows one to further refine the injection strategy by adjusting injection pressure to account for washout in high injection pressure resin transfer moulding.

Development of full carbon wheels for sport cars with high-volume technology

Aim of the paper is to present the methodology used to develop a new process, based on high-pressure resin transfer molding (HP-RTM), to produce full carbon reinforced plastic rims for sports car. These components are nowadays made by pre-preg autoclave processing, which is expensive and time-consuming, so that they are basically sold as aftermarket option. The proposed technology allows a manufacturing volume high enough to be suitable for series production. In this paper, the resin and fiber selection criteria and tests are shown, as regards the mechanical properties, durability and injection strategies.

Forming Characteristics with Cavity Pressure and Temperature Signal Inside Mold in High-Pressure Resin Transfer Molding Process of Carbon Fiber Reinforced Composite Material

Forming Characteristics with Cavity Pressure and Temperature Signal Inside Mold in High-Pressure Resin Transfer Molding Process of Carbon Fiber Reinforced Composite Material