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Liquid Composite Molding (LCM) techniques including the Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM) are gaining significant importance for fabricating aerospace and automotive composite parts, owing to the low investment costs. During the curing process, the resin undergoes a property change due to cross-linking of polymers, where it transitions from the liquid state to the solid state. Further, during the cooling process, there is a change in the glass transition temperature, resulting in residual stress and strains. The residual strain and deformations accumulated during the curing of the resin at high temperatures result in significant challenges to the final part shape and performance of the composite structure. This research presents a thermo-chemo-mechanical curing model for liquid composite molding processes, which is validated with in-situ sensor monitoring data including viscosity, temperature, and degree of cure using dielectric sensors, and the distribution of induced strains during the curing process using distributed optical sensors. The viscoelastic curing model developed in ABAQUS constitutes of the resin cure kinetics, viscoelastic resin properties, and thermal and stress analysis components. A case study is performed for an angle bracket, where the resulting cure-induced stress deformation is observed and validated, and the spring-in angle of the bracket is predicted.

Experimental permeability measurements saw a considerable increase in accuracy when recommendations and guidelines were imposed upon the realization of two international benchmarks. Such requirements aid the design stage and experimental validation of a permeameter rig however, systematic errors in the measurements still compromise the comparability of measurements obtained by different radial permeameter rigs. Owing to hurdles and limitations in the data acquisition system, validation of the mold cavity and fluid injection system, optical errors in the visual tracking of a flow front, and uncertainties in the measurement of the fluid viscosity, the measurement’s accuracy is yet lower than the required for a standardized process. In this study, the detailed study and calibration of such parameters was able to identify and minimize error sources that would otherwise result in undetected systematic deviations from the expected results. In conclusion, the verification proposed by the radial benchmark does not guarantee the accuracy of the measurement, as the error in the instruments proposed for the verification is comparable to the requirements themselves. This creates a certain uncertainty in the verification that needs to be tackled with more detailed measurement protocols to ensure not only the compliance with the measurement requirements but also to set the limits of the attainable accuracy. The rig was validated by measuring the permeability of the fabric reinforcements used in the radial benchmark exercise. Due to the scattering in the results reported in the benchmark exercise, 13 out of the 19 reported values were excluded to obtain a good estimation of the expected permeability for each volume fraction. Although the rig complied with all recommendations currently in place, the obtained permeability showed a 20% deviation in the K1 direction, while the K2 was within the expected range for the average value. The observed deviation was later found to be caused by an optical distortion, which affected the measurement of the real-world flow front dimensions. A correction for this deviation needs further systematic investigation, also a possible revision of the future standard since a correction for optical distortions is yet not included in the measurement guidelines.

Lately, researchers around the world have developed effective chemical and physical treatments on plant fibers to improve their compatibility with polymeric matrices. In addition, the need of high performance fabrics produced from plant fibers has been addressed by many manufacturers of textile reinforcements. These facts have increased the use of natural fibers in the composite industry. Liquid composite molding (LCM) techniques are suitable for mass production of high-quality composite parts. Basically, the reinforcement is compressed inside a mold and a thermosetting resin is injected to impregnate the fibers and fill the empty spaces in the mold. After the resin cures, the composite part is demolded. However, the processing of plant fiber–reinforced composites by the traditional techniques is not trivial, because the structure of plant fibers is more complex than that of synthetic fibers and due to their chemical composition rich in cellulose and hemicellulose, they are highly hydrophilic. This work presents a review on the main issues that arise during the processing of plant fiber reinforced composites by traditional liquid composite molding techniques. Fil: Francucci, Gaston Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Rodriguez, Exequiel Santos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

International audience; Introduction With the increased use of Liquid Composite Moulding (LCM) processes in the aeronautical and automotive industries, the complexity of the parts and quality requirements have increased tremendously. The development of fabric forming models and the refinement of mould filling simulations, calls for improved material models to achieve the predictions expected by the industry. Accurate permeability data of reinforcing materials is essential in order to conduct LCM simulations and design the manufacturing process more efficiently [1]. Permeability is predominantly a function of the reinforcement architecture and its fibre volume fraction, both of which are affected by textile deformation when used to manufacture complex 3D parts. The push for more sustainable materials either biodegradable or fully recyclable has also pushed the composite industry to look increasingly at bio-based reinforcements and resins. The bio-based reinforcement being formed from the assembly of short fibrils of variable geometry into continuous strands have very different forming and permeability properties than traditional composite reinforcements formed by assembling continuous fibre with smooth geometry.