Gaston Francucci

Experimental study of the compaction response of jute fabrics in liquid composite molding processes

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.

Key differences on the compaction response of natural and glass fiber preforms in liquid composite molding

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.

Thermal conductivity of sandwich panels made with synthetic and vegetable fiber vacuum-infused honeycomb cores:

Building, naval, and automotive industries have deep interest in eco-friendly, lightweight, stiff and strong materials. In addition, materials with low thermal conductivity are desirable in many applications where energy savings and thermal comfort are needed. In response to these requirements, sandwich panels were manufactured using glass and jute fiber composite skins bonded to different cores: balsa wood, Divinycell® and honeycombs. These honeycombs, as well as the skins, were manufactured by the vacuum infusion technique using polyester resin and jute, glass and carbon fiber fabrics. In this work, the thermal properties and density of the sandwich panels were measured and compared.

Novel approach for mold filling simulation of the processing of natural fiber reinforced composites by resin transfer molding

Modeling the infiltration of reinforcements during the processing of composite materials by liquid composite molding techniques is an important instrument for the prediction of flow front patterns, filling times and pressure gradients. Darcy’s law is widely used to model most of these processes. However, when polar fluids are used together with natural fibers, fiber swelling may occur and introduce further complexity to the simulation. In this work, a model that includes the aforementioned phenomena is proposed, leading to a more accurate prediction of the flow front position than the classic models that use a constant permeability value.

The mechanical properties of flax fibre reinforced poly(lactic acid) bio-composites exposed to wet, freezing and humid environments

Bio-composites are increasingly being perceived as a green alternative to synthetic composites in many applications. However, the overall long-term durability of bio-composites is a major concern, particularly their ability for sustained performance under harsh and changing environmental conditions. This paper reports a detailed study on the effect of environmental conditions on the performance of flax/poly(lactic acid) bio-composites. Neat poly(lactic acid) and bio-composite samples were exposed to environments similar to those found outdoors: wet, freezing and humid. Moisture absorption and physical changes of specimens were periodically examined. Flexural and tensile properties were evaluated periodically to determine the detrimental effect of each exposure condition on the mechanical performance of bio-composites. Direct contact with liquid water is the most deteriorating environment for bio-composites. A drying process can partially restore the mechanical performance of these materials. Bio-composites can survive reliably in warm humid environments and in those that could create freeze and thaw cycles for short-term outdoor applications. The mechanisms and reasons involved in the degradation of the properties of green composites are discussed.

Effect of Moisture in Flax Fibres on the Quality of their Composites

ABSTRACT Moisture present in plant fibres is considered to be detrimental to the performance of composites. In general, a drying stage is performed on the plant fibre fabrics before manufacturing the composites since it is seemed to allow better output. This work provides an analysis of the effect of moisture in flax fibres on the overall quality of epoxy/flax biocomposites. Flax fibre fabrics were conditioned at different relative humidity (RH) environments and composites were manufactured by vacuum infusion technique. Composites were characterized by mechanical and microstructural analysis. Results showed that manufacturing composites with highly humid fabrics (95% RH) generates post processing deformation of finished parts and also leads to poor microstructural quality. The moisture in the fibres with different RH reduced the stiffness (from 23.74 to 17.67 GPa for Young’s modulus and from 16.28 to 11.82 GPa for flexural modulus) but increased their fracture strain (from 1.87 to 2.64). Tensile strength displayed an optimum value (287.96 MPa) for fabrics conditioned at 50% RH, but flexural strength decreases continuously from 225.12 to 152.34 MPa as the moisture in the fabric increases.

PHB coating on jute fibers and its effect on natural fiber composites performance

In this work, a novel treatment on plant fibers is presented and its effect on the mechanical properties and water absorption of vinyl ester matrix composites is analyzed. The treated fibers used in this study consisted in alkaline-treated jute fibers and alkaline-treated jute fibers coated with polyhydroxybutyrate (PHB). Bending tests and IZOD impact tests were performed to evaluate the mechanical performance of the composites. The samples were immersed in water (at room temperature and at 80℃) and the water sorption and flexural modulus were measured in time. Flexural strength and impact energy were measured on dry specimens and the detrimental effect of water on those properties was evaluated by testing the samples after the immersion tests. The composites manufactured with alkali-treated fibers coated with PHB showed the best performance in terms of water absorption and mechanical properties.

On the Dynamic Performance of Flax Fiber Composite Beams Manufactured at Different Relative Humidity Levels

ABSTRACT Development of environment-friendly natural fiber composites has been a recent trend. However, due to the fact that natural fibers permit high level of moisture absorption from the surroundings, it can lead to weak bindings and degradation of composite properties. This paper presents an experimental study on the dynamic performance of flax fiber composite beams manufactured at different relative humidity (RH) levels. Five types of flax fiber-reinforced composite materials were made under different RH values, i.e., dry, 35%, 50%, 70%, and 95% RH, and beam samples were prepared using the composite. Impact hammer testing was conducted to measure the natural frequencies and damping of the beams. It was found that for the first three modes, while the resonant frequencies are very close for most samples, there is a clear drop of frequencies for the composite fabricated at 95% RH. Along with an increase of the RH level, the damping ratios for all the three modes have reported a slight increase, but the variation is not significant.

External compaction pressure over vacuum-bagged composite parts: effect on the quality of flax fiber/epoxy laminates

Vacuum bagging allows the removal of trapped air between fabrics layers, extraction of moisture and volatiles, and optimization of the fiber-to-resin ratio. However, during vacuum bagging the compaction pressure is limited to atmospheric pressure, preventing the composite reaching higher fiber volumetric contents and also allows surface porosity to arise, affecting the esthetical appearance of the composite and also its mechanical performance. While the autoclave process has shown to solve these problems, the cost of the equipment is too high for many applications. In the present work, a series of experiments are carried out by compressing unidirectional flax/epoxy vacuum-bagged laminates in a hydraulic press at different pressures. The quality of the laminates is analyzed in terms of surface finish, internal void content, and mechanical properties. The additional compaction from hydraulic pressure is shown to be very effective in improving considerably the overall quality of the composites.