Chung Hae Park

Analytical Modeling of Composite Molding by Resin Infusion With Flexible Tooling: Vari and rfi Processes

We present analytical modeling and closed form solutions for composite resin infusion processes such as the vacuum assisted resin infusion (VARI) process and the resin film infusion (RFI) process. As a flexible bag is placed on the top of fabric stack, while a rigid tooling is still used on the other side, a fabric deformation takes place as the resin pressure changes during the resin infiltration process. Subsequently, it is important to take into account the reinforcement compaction as well as the resin flow in the analysis of resin infusion processes. We present a fully analytical modeling of resin pressure distribution, resin flow front position, fiber volume fraction distribution, and part height change during the resin infusion process. Parametric studies are provided to investigate the influences of process parameters on the process feasibility. The evaluation of bulk permeability in the RFI process implies that the fabric compaction should be taken into account to exactly characterize the through-thickness permeability of fibrous reinforcement.

Analytical modeling and in situ measurement of void formation in liquid composite molding processes

Liquid composite molding processes are widely accepted in the aeronautic industry to manufacture large and complex structural parts. In spite of their cost-effectiveness, void defects created during the manufacturing process are a major issue of these processing techniques because they have detrimental effects on the mechanical performance. The reliable modeling is still a difficult task and experimental observations are usually adopted for the analysis of void formation mechanism, however, because many different physics are simultaneously involved during the mold filling process and the resin curing process. The complexity of the void formation physics implies the need for an in situ measurement of void formation not in the final part but in the mold filling procedure during the manufacturing process to better understand the void mechanism. In this regard, we present a sensor system measuring the electric conductivity for the in situ monitoring of void formation during the mold filling process. We also propose a theoretical model to predict void formation in a quantitative way with the properties of the resin and the fiber reinforcement. The model prediction is compared with the experimental data obtained by the sensor system to validate the model.

Simple models and optimization of compression resin transfer molding process

The optimization of the couplings between LCM processes and structural performances by repeated numerical simulations is expensive in terms of the computational cost. In order to overcome this difficulty, we propose a semi-analytical modeling of RTM and CRTM processes. Various processing routes of CRTM are considered according to the combinations of different stages of resin injection and reinforcement compression. This article is composed of two parts. First, we present analytical and semi-analytical models concerning the CRTM process with an imposed compression speed, in order to explain the methodology of resolution for the other CRTM manufacturing routes by an imposed compression force. The problems related to different constraints imposed on the CRTM process (imposed fiber volume fraction, feasibility criteria of process, and mold strength) are analyzed and formulated, so that they can be taken into account a numerical optimization. In the second part, a new numerical modeling of CRTM process with reinforcement compression under a force was developed and a comparison with semi-analytical model carried out. Recent work in the literature [Merotte J, Simacek P and Advani SG. Flow analysis during compression of partially impregnated fiber perform under controlled force. Compos Sci Technol 2010; 70: 725–733.] about the analysis of resin flow during compression of partially impregnated fiber preform under controlled force, allowed us to explore another alternative of comparison. Finally, this approach is used to control the RTM and CRTM processes and it is applied to a series of parametric studies, considering the effects of part size and fiber volume fraction on the mold filling time. This study not only contributes to the optimization of the couplings between manufacturing processes and structure, but also provides a tool for the control of the CRTM and RTM processes.

Air Entrapment Simulation in the Resin Transfer Molding of Industrial Applications

Abstract. We present numerical simulation of air entrapment in composite materials manufactured by the resin transfer molding (RTM) process. The prediction of air void formation has been an important topic because air voids in composite materials deteriorate the mechanical properties of the part. Two kinds of voids can appear when the resin is injected inside the fiber preform: the first one at a microscopic scale and the second one at a macroscopic scale. In the work proposed here, we focus on the study of void formation at the macroscopic scale. The adopted modeling principle is based on a two-phase flow analysis. We compare the two-phase flow analysis results with the single-phase flow analysis results commonly used in the resin injection simulation.

Integrated optimization for weight, performance and cost of composite stuructures

Abstract A structure-process integrated optimization methodology is proposed considering both the structural properties and manufacturing process for the weight minimization of composite laminated plates manufactured by Resin Transfer Molding (RTM) process. In the optimization problem, the structural weight of composite structures is minimized under the stiffness constraint and the mold filling time constraint which is a part of process cycle time. With the results obtained, it is investigated how the weight and material cost are traded-off. The optimization methodology suggests a guide of material selection in the preliminary conceptual design stage.

Forming Simulation of Automotive Part in Woven Composite Material

In the present work, a thermo-visco-elastic model for forming simulation of woven thermoplastic composites has been proposed considering the effect of temperature and the influence of strain rate. This model is implanted into a new membrane finite element, which can consider not only the strain in fibre direction but also the shear caused by the relative movement of weft and warp during the deformation of woven composite material. The simulations of bias-test have been performed to validate this method. Finally, the forming process of an automotive part in woven composite material is simulated with this method.

Multidisciplinary Optimization of Composite Laminates with Resin Transfer Moulding

In this study, a multidiscplinary optimisation methodology of composite structures with the Resin Transfer Moulding (RTM) process is suggested in order to satisfy both the structural and the process requirements. Among the composite manufacturing techniques, the RTM process is distinguished for its own many advantages such as low manufacturing costs, complex shapes, high productivity, and good mechanical performance. In designing composite structures with the RTM process, tailoring the fibre preform architecture plays an important role as well as deciding the injection strategy. With some appropriate assumptions, a simplified optimisation method is suggested to find a near optimal design configuration. At first, the number of fibre mats, the stacking sequence of layer angles and the injection gate locations are found in order to satisfy the structural criteria, such as the stiffness requirement, and the process criteria, such as the mould filling time. Then, the thickness of the composite laminate and the fibre volume fraction are determined so as to reduce the weight keeping all the design criteria satisfied. This problem is a multi-objective optimisation problem and hence an objective function is appropriately formulated. As an optimisation technique, a genetic algorithm is used. The reliability of the present design methodology is assessed with some examples.