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In this study, nanoalumina (Al2O3) and nanosilica (SiO2) particles are evaluated as tougheners for a high glass-transition temperature (Tg) epoxy system in correlation with liquid composite molding (LCM) processability. The aim of this paper is to directly compare the effectiveness of nanoalumina and nanosilica of the same nominal particle size as epoxy tougheners on the same neat resin system. The epoxy resin system used in this study was Dow D.E.R. 330 amine cured epoxy with a Tg of 150℃. Both particle types are observed to be Tg neutral and increase fracture toughness of the base epoxy system. Between the two particle types, nanoalumina is found to be more effective than nanosilica in terms of achievable fracture toughness at a given particle loading. As resin viscosity increases with particle addition, the addition of fewer particles with the use of nanoalumina is also beneficial to LCM processing where a lower viscosity is preferable. [ABSTRACT FROM AUTHOR]

In the present work, the effects of fiber structure and fluid absorption on the compaction behavior of jute woven fabrics and sisal mats were analyzed and compared with the response of glass fiber mats. It was found that the fiber content that can be achieved with a certain compaction pressure is lower in the case of natural fiber preforms. In addition, due to the hollow structure of these natural fibers, jute and sisal preforms suffered larger permanent deformation than glass fiber preforms after the compressive loading cycle. In addition, it was found that fluid absorption reduced the compaction pressure in natural reinforcements due to fiber softening. These phenomena were not observed in glass fiber mats. [ABSTRACT FROM PUBLISHER]

The aim of this work is to characterize the compaction behavior of jute woven fabric preforms. The maximum compaction pressure, permanent deformation, and stress relaxation of the preforms were found to be dependent on the final fiber volume fraction and the compaction speed. Higher compaction speeds led to higher compaction pressures, stress relaxation, and permanent deformation. On the other hand, as the fiber content was raised, the maximum compaction pressure and the permanent deformation increased, while the stress relaxation decreased. In addition, it was found that the structure of natural fibers affected the compaction behavior of the preforms. Each fiber is composed of several hollow elementary fibers, which collapsed due to the compressive loading. Furthermore it was found that fluid absorption reduced the compaction pressure in natural fiber preforms due to fiber softening. [ABSTRACT FROM AUTHOR]

Computer simulation has become an efficient and cost-effective tool for the liquid composite molding (LCM) processes, including the RTM, VARTM, and resin infusion, compared to trial-and-error. The purpose of simulation is to accurately reflect the real situation. Since the simulation is predominantly based on the control volume finite element method (CVFEM), the boundary conditions such as gate and vent definition need to be properly defined. In this paper, the errors of the CVFEM based mold filling simulation were analyzed. The error sources were identified as the mesh near gates and vents, and gate definition. By conducting 3-D and 2-D simulation case studies, the influence of the gate definition on the simulation result was studied. Because many composite parts are shells and can be regarded as surfaces. 2-D simulation is favorable because of the better efficiency and simpler pre-processing. For this purpose, a method for mold filling simulation incorporating the gate size effect the effective gate method (EGM) - was developed. This method was validated through case studies. It shows that the EGM provides an effective and efficient approach to the CVFEM mold filling simulation incorporating the effect of injection gate size. [ABSTRACT FROM AUTHOR]

In liquid composite molding technologies such as RTM, this study of the inlet-pressure history for the constant flow-rate 1-D flow experiment reveals that the measured pressure profile, which droop downwards as in earlier studies on the unsaturated flow, is at a variance with the linear pressure profile predicted by the physics used for state-of-the-art LCM mold filling simulations. The droop along with the error in the inlet-pressure predictions increase with an increase in the fiber-mat compression. The effect of fiber-mat architecture on the droop in the inlet-pressure profiles is studied and significant droops are observed for various stitched mats as compared to the woven mats. This study repudiates the long-held view that mere presence of cylindrical or elliptical tows in the woven or stitched fiber-mats automatically leads to the unsaturated flow characteristic of dual-scale porous media; rather the presence of continuous uninterrupted macrochannels along the flow direction for preferential channel-flow is found to be necessary for the appearance of a drooping inlet-pressure history characteristic of the unsaturated flow. [ABSTRACT FROM AUTHOR]

Three types of dry spot changes, which have been described in Part I, are modeled in this study. Darcy's law and ideal gas law are used to model the Type I and Type II dry spot changes, while a simplified form of the two phase Darcy's law is used to model the Type III dry spot change. A computer code based on the control volume finite element method is developed to simulate the dry spot formation and changes. In order to save computation time, a coarse mesh rebalancing method is implemented in the code. Compared to the experimental results, this flow model predicts the Type I and Type II dry spot changes and the packing and bleeding process very well. It shows the right trend of Type III dry spot changes when compared to some preliminary experimental results. [ABSTRACT FROM PUBLISHER]

Dry spot formation and changes in liquid composite molding (LCM) were investigated by flow visualization experiments. The dry spot size can be reduced by three mechanisms: (1) it can be compressed by the hydrostatic pressure from the surrounding saturated region; (2) it can be reduced by bleeding trapped air into the surrounding saturated region if there is a pressure gradient in the saturated region; and (3) it may gradually disappear by the wicking flow due to the capillary pressure difference between the saturated region and the dry fiber region. Experiments of packing and bleeding, a technique used in industry to eliminate dry spots, were also carried out and the results are explained based on the three types of dry spot changes. [ABSTRACT FROM PUBLISHER]