Papers by Keyword: Liquid Composite Molding

Abstract: Novel multifunctional resins and composites present multiple manufacturing challenges that need to be overcome to allow for wider adoption. These challenges include high viscosity, short cure windows, low permeability preforms, and non-standard cure kinetics. Standard liquid composite molding methods (such as resin infusion under flexible tooling [RIFT], resin transfer molding [RTM], or compaction-RTM) are poorly equipped to manufacture these new materials. A new system is presented that combines the abilities of RIFT/RTM/c-RTM while introducing controlled deformation of the preform during infusion to remove flow through the preform. This manufacturing method allows the preform to lie uncompacted, while still under vacuum, during infusion which allows resin to flow unrestricted between plies. Then once infusion has occurred, compaction proceeds to produce the final composite geometry. This method has been successfully implemented to manufacture structural power devices with a biphasic resin system and metal coated carbon aerogel preform, as well as a vitrimer composite with a high-viscosity/short-cure resin thought high weight carbon fiber preform. The novel and flexible manufacturing parameters of this new system present a low-cost route towards optimizing the manufacture of challenging and novel resin systems, allowing for a faster understanding and implementation of these materials.

Abstract: Liquid Composite Molding (LCM) processes, used for producing high-quality, complex composite parts, rely on the uniform infiltration of liquid resin into fibrous fabrics. These fabrics possess a dual-scale structure: highly porous inter-tow spaces surrounding denser fiber tows. The resulting disparity in permeability and flow rates is a primary cause of defect formation, such as voids. To minimize these defects, accurate simulation, incorporating the critical influence of capillary pressure on resin infiltration within the fiber tows, is essential. This work presents a robust numerical model developed to simulate the two-phase resin flow and impregnation dynamics within a digitized, real plain-weave E-glass reinforcement obtained via X-ray micro-computed tomography (CT). The simulation utilizes the open-source multiscale multiphase solver, hybridPorousInterFoam, which employs a Darcy-Brinkman approach, transitioning between Darcy's law in porous regions and Navier-Stokes in free space. A key methodological enhancement involved modifying the advection algorithm using the isoAdvector scheme to mitigate numerical instabilities caused by the high viscosity ratio between the resin and air. Capillary effects at the mesoscale are incorporated through multiscale parameters, specifically the drag and surface tension forces. The key findings demonstrate that the modified solver successfully handles the fluid-fluid interface advection for high viscosity ratios. A parametric study highlighted the significant effect of capillary pressure on multiphase flow within the dual-scale porous media. The numerical results for flow front advancement showed very good agreement when compared against dedicated experimental validation data, confirming the model's high predictive accuracy and its potential for optimizing LCM injection conditions.

Abstract: Among the existing techniques for composite materials manufacturing, Vacuum Assisted Resin Infusion (VARI) is a liquid composite molding (LCM) process where resin flows through a dry fiber preform to fully impregnate it. This method uses flexible film sealed onto a rigid mold to form the infusion cavity containing the fibers. As the fabric preform is impregnated, its thickness varies due to the changes in the applied compaction pressure. This thickness variation affects the resin flow and the final fiber volume fraction of the manufactured part. This study focuses on the initial steps of developing an integrated acquisition system for thickness variation monitoring during VARI. The conventional flexible tooling is to be replaced by a flexible membrane equipped with optical fiber Bragg grating (FBG) sensors. A prototype was developed by embedding FBG sensors in a silicon rubber material and initial measurements of a cylindrical profile curvature were performed. Preliminary results show satisfactory precision of the device, which opens a gap for a more precise and accurate thickness monitoring process during real part manufacturing.

Abstract: Liquid composite molding (LCM) is a widely used group of various different processing techniques allowing to produce small, medium or even very big sized components from prototype level up to series production. During the infiltration it is necessary to run the process in a way preventing void formation. The typically used textile reinforcing structure results in a dual-scale impregnation consisting of micro impregnation within the constituent yarns of the textile structure and a macro impregnation between the yarns. Capillary rise experiments on flat textile samples are used and the well-known Lucas-Washburn equation has been extended to cover the special configuration. A porous capillary wall is assumed to better represent the three-dimensional nature of capillary networks within reinforcing textiles. An according test rig is presented. Accurate experimental results are gained and capillary radii are computed simple and fast via curve regression.

Abstract: Compression resin transfer molding using inflatable seals is a new variant of LCM (“Liquid composite molding”) processes, which uses the inflatable seals to compress the fiber reinforcements and drive the resin to impregnate the fabric preform, resulting to fill the entire mold cavity. During resin injection, the preform is relaxed. Consequently, the resin enters easily and quickly into the mold cavity. After, the necessary resin is injected into the mold cavity, the compression stage takes place, in a stepwise manner, by swelling the inflatable seals. The objective of this paper is to present this new process and study the effect of the number of inflatable seals on the filling time.

Abstract: 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.

Abstract: Composite materials do offer freedom to design a material fitting best to the requirements of a given application. In case of fiber reinforced polymers especially the low weight in combination with other favorable properties, e.g. high mechanical performance, are the driving force for their application. Materials from renewable resources are of high interest if sustainability is aimed. In this paper, in a holistic approach a green composite is aimed to be used in a rotor blade for wind energy production. The challenging topic for this approach is to identify a possibility to gain a thermoset resin being really green, i.e. based on renewable resources and being not critical, e.g. toxic, at any stage of the whole processing chain. For this purpose several different approaches are studied and compared with other solutions based on green resin systems from other resources and conventional petrochemical based resin systems. A hemp seed oil based epoxy resin has been tested successfully. But to be completely free of petrochemicals, bio-based hardener and catalysts are still an open topic. For manufacturing of a rotor blade an infusion process has been used and it was found, a through thickness impregnation of the natural fiber yarn based textile structure results in entrapped air. Only in-plane saturation delivered completely impregnated structures.

Abstract: This paper presents the development of a novel omega-shaped resin transfer molding (RTM) tool, which is especially designed to host different types of sensors and to avoid common problems of RTM (e.g. uneven heating, low tool durability, deflection). Permeability measurements were executed in order to get real permeability measurements for numerical mold filling simulations. Three different kinds of flow behaviors (isotropic, orthotropic and anisotropic) were considered as filling patterns and the flow front predictions. Due to the U-shaped composite part design, the mold curvature effects on the flow front propagation caused by the increased fiber volume content in these areas were also taken into account. The tool was designed with a heating ability using purified liquid water guided to a channel circuit within both top and bottom halves of the tool. Deflection and heat transfer simulations were performed with the finite element method (FEM). All three executed simulations (filling, heat transfer and deflection) were used as a guideline for the final mold design.

Abstract: The aim of the present work is to investigate the influence of the Vacuum Assisted Resin Transfer Molding process steps on the impregnation quality of the laminates as well as on mechanical and tribological properties of the processed material. Composite laminates were realized using epoxy resin reinforced with carbon (CF) or glass continuous (GF) fibers. Two different textile architectures, namely non-crimp fabrics (UD) and woven-mat (0/90), were used and various processing conditions were employed. Optical observations revealed an unexpected trend relatively to the intra and inter bundle voids concentration with respect to the impregnation velocity, especially using UD-CF and UD-GF reinforcements and low impregnation rate. Tensile and three points bending tests highlighted the strong impact of fiber material and architecture on mechanical properties, whereas the presence of voids played a slightly influence on the fiber dominated characteristics analyzed. Tribological outcomes evidenced a reduction of the friction coefficient when the resin is reinforced by carbon or glass fibers as well as when the sliding direction of the counterbody is oriented parallel to the fiber direction.

Abstract: The properties of heat resistance and manufacturability of epoxy resin system are contradictory to each other. In order to maintain the balance of both properties, this article studied the heat resistance (testing the glass-transition temperature using differential scanning calorimetry) and the manufacturability (characterizing the variation trend of viscosity at molding temperature using AR2000EX rotational rheometer) of two kinds of epoxy resin systems by means of designing orthogonal table. Studies show that when the mass ratio of hydantoin epoxy resin, MF-4101 epoxy resin, anhydride and accelerant is 100:20:150:1.5, the glass transition temperature of the epoxy resin system can reach over 180°C. What’s more, the initial viscosity of the epoxy resin at 40°C is about 230mPa•s, and the viscosity can maintain no more than 800mPa•s in approximately 3 hours, which meets the requirements of liquid composite molding.