Fiber volume ratio | EPFL Graph Search

Fiber volume ratio is an important mathematical element in composite engineering. Fiber volume ratio, or fiber volume fraction, is the percentage of fiber volume in the entire volume of a fiber-reinforced composite material. When manufacturing polymer composites, fibers are impregnated with resin. The amount of resin to fiber ratio is calculated by the geometric organization of the fibers, which affects the amount of resin that can enter the composite. The impregnation around the fibers is highly dependent on the orientation of the fibers and the architecture of the fibers. The geometric analysis of the composite can be seen in the cross-section of the composite. Voids are often formed in a composite structure throughout the manufacturing process and must be calculated into the total fiber volume fraction of the composite. The fraction of fiber reinforcement is very important in determining the overall mechanical properties of a composite. A higher fiber volume fraction typically resul

Novel tooling for direct melt impregnation of textile with variotherm injection moulding: Methodology and proof of concept

Véronique Michaud, Christian Rytka, Vincent Werlen

Thermoplastic compression resin transfer moulding coupled with injection moulding is an appealing process for the production of thermoplastic composites. However, its implementation at an industrial scale remains challenging as variotherm injection moulding could prevent solid skin formation in the parting line, making cavity sealing difficult. In this study, a tool for thermoplastic compression resin transfer moulding and the related methods and process parameters for an implementation at an industrial scale are presented. The validity of the concept is proved by producing and characterizing composite plates with elevated fibre volume fractions and advantageous mechanical properties at a range of production temperatures within a cycle time not exceeding 20 min. The best mechanical properties were obtained at a production temperature of 270 degrees C with a bending strength of 477 MPa, a flexural modulus measured at 25.7 GPa and a fibre volume content of 67%.

SAGE PUBLICATIONS LTD2022

Translucent load-bearing GFRP envelopes for daylighting and solar cell integration in building construction

Carlos Pascual Agullo

This project investigates the light transmittance of load-bearing glass fiber-reinforced polymer (GFRP) laminates with a view to two architectural applications: the daylighting of buildings through load-bearing translucent GFRP envelopes and encapsulation of solar cells into the GFRP building skins of sandwich structures. The total and diffuse visible light transmittances of the laminates were experimentally investigated using a spectrophotometer coupled to an integrating sphere. The refractive indices of polymeric resin and glass fibers were also investigated and numerical ray-tracing simulations were performed to demonstrate the experimentally observed wavelength dependency of light diffusion. The total transmittance and translucency of GFRP laminates were analytically modeled as a function of the reinforcement weight, fiber architecture and fiber volume fraction. Goniophotometric experiments – performed to investigate the directional light scattering of laminates reinforced with different fiber architectures – were demonstrated as an effective method to predict the fiber architecture of translucent GFRP laminates. The optical properties of the laminates, i.e. the total and diffuse transmittances and directionality of light diffusion, were correlated with the experimentally investigated mechanical properties, i.e. the directional tensile strength and E-modulus. The experimental work demonstrated that structural skylights could be designed with GFRP laminates exhibiting a translucency of 0.9 and total light transmittance of 0.5 – minimum values recommended for daylighting of buildings through translucent envelopes – and that solar cells could be encapsulated in load-bearing GFRP laminates with a total light transmittance of around 0.83. A case study was performed using the GFRP/polyurethane sandwich roof of the Novartis Campus Main Gate Building to demonstrate the basic feasibility of integrating skylights and solar cells into the external translucent skin of optimized sandwich structures. Finally, the encapsulation of transparent and colored dye solar cells in translucent GFRP laminates has been explored. Prototype solar panels have been fabricated and a significant weight reduction, increase in structural strength and around 10% reduction of electrical efficiency compared to traditional solar panels with glass encapsulants were achieved.

EPFL2014

Assessment of solvent capsule-based healing for woven fibre-reinforced epoxies

Erica Manfredi

Structural fibre-reinforced composites based on brittle matrices such as epoxy resins may be subject to short-term subcritical matrix damage that develops with time to the point where it may compromise the integrity of the structure. Currently, components that have been damaged at the microscale are usually inspected and, depending on the extent of the damage, repaired with patches or entirely replaced. Self-healing functionality would prevent development of such damage by repairing it as soon as it appears, thereby increasing the service life of the material. Among the many potential methods for introducing self-healing capacity to epoxy resins, incorporation of solvent-filled capsules is particularly promising. Cracks cause the capsules to break, releasing a solvent that is able to swell the crack faces and induce reaction of residual monomer and/or crosslinkable functional groups intentionally left by under-curing the matrix. Thus, a model system based on ethyl phenylacetate (EPA) has been shown to provide up to approximately 90% efficiency in recovering fracture toughness, and to effectively block fatigue crack propagation in pure epoxy resin. The present thesis focuses on the integration of a EPA solvent capsule-based healing system into a glass fibre-reinforced epoxy and the assessment of its effectiveness in repairing static interply damage. EPA-filled capsules with diameters in the range of 90-250 ÎŒm were produced using an oil-in-water emulsion technique and characterized in terms of their thermal stability and mechanical properties. Pure urea-formaldehyde (UF) as well as polyurethane/urea-formaldehyde (PU/UF) double wall capsule shell materials were analysed, showing that the wall thickness of pure UF capsules is independent of their diameter, whereas that of PU/UF capsules is 4 to 6 times greater and scales with the capsule diameter until a saturation value. The modulus of these shell materials was quantified using compression test and an analytical model, and found to range from 1 to 4 GPa depending on the amount of PU content in the shell composition. Bursting forces varied from 5 to 25 mN depending on the shell composition and diameter, thus providing a range of shell compositions to select from in order to tune the capsule behaviour. The integration of the capsules into the composite was carried out by dispersing them manually onto the reinforcement textile prior to processing. During this phase, the optimum capsule size range, position and concentration could be selected to fit in the interstices and survive textile packing. Textile packing properties were tested in compression; the presence of capsules led to a decrease of the reinforcement volume fraction at a given applied load value, in particular at low packing loads, and affected the usual power law behaviour of a textile in compression, up to the rupture of the capsules. Longitudinal permeability was also increased by a factor of 6 to 8 in presence of capsules for a given reinforcement volume fraction, whereas the transverse permeability was not greatly affected. A capsule-containing fibre-reinforced epoxy material was then produced using a suitably adapted processing protocol. Vacuum assisted resin infusion moulding (VARIM) was chosen as an industrially relevant, yet adaptable processing route. Priority was given to industrially relevant fibre volume fractions of approximately 50% and to optimizing processing parameters such as the lay-out and vacuum etc.

EPFL2015