Gilbert Lebrun

Experimental investigation of the cutting temperature and surface quality during milling of unidirectional carbon fiber reinforced plastic

The surface machining of carbon fiber reinforced plastics materials is a challenging process, given the heterogeneity and anisotropic nature of composites, which, combined with the abrasiveness of the fibers, can produce some surface damage and extensive tool wear. The cutting temperature is one of the most important factors associated with the tool wear rate and machinability of these materials, which are also affected by the mechanical and thermal properties of the workpiece material and the cutting conditions. In this work, the cutting temperature, cutting forces, and composite surface roughness were measured under different cutting conditions for the end milling of unidirectional carbon fiber reinforced plastics. Cutting speeds ranging from 200 to 350 m/min; a feed rate of 0.063 mm/rev; fiber orientations of 0, 45, 90, and 135°; and a 0.5 mm depth of cut were considered. The results show that the cutting speed and fiber orientation have a significant influence on the cutting temperature and cutting forces. The maximum and minimum cutting forces and temperatures were achieved for fiber orientations of 90 and 0°, respectively.

Experimental characterization of short flax fiber mat composites: tensile and flexural properties and damage analysis using acoustic emission

Abstract In this work, tensile and flexural tests are realized on composites reinforced with short flax fibers mats produced by a papermaking process. Plates are molded with different fiber volume contents (Vf), and to support the analysis, acoustic emission (AE) is coupled to test samples to follow the evolution of different damage modes using a multivariable analysis to classify the acoustic events. It is shown that the tensile and flexural properties increase with Vf up to a critical value of about 40%, above which they start to decrease. The contribution of each damage mode in the global failure of the composites is calculated, and their effect in the evolution of mechanical properties is discussed. The results show that compared to the tensile tests, AE events of flexural tests appear at much higher strains, with considerably lower cumulated energies, reflecting the low level of AE events attributed to matrix microcracking. The AE analysis also reveals a clear domination of fiber–matrix friction and fiber pullout mode of fracture, raising the importance of the adhesion of flax fibers–epoxy matrix. The decrease in Young’s modulus and strength at Vf above 40% is in a large measure explained by a poor fiber–matrix adhesion.

Effect of cutting tool lead angle on machining forces and surface finish of CFRP laminates

Abstract Machining is one of the most practical processes for finishing operations of composite components, allowing high-quality surface and controlled tolerances. The high-precision surface milling of carbon fiber-reinforced plastics (CFRP) is particularly applicable in the assembly of complex components requiring accurate mating surfaces as well as for surface repair or mold finishing. CFRP surface milling is a challenging operation because of the heterogeneity and anisotropy of these materials, which are the source of several types of damage, such as delamination, fiber pullout, and fiber fragmentation. To minimize the machining problems of CFRP milling and improve the surface quality, this research focuses on the effect of multiaxis machining parameters, such as the feed rate, cutting speed, and lead angle, on cutting forces and surface roughness. The results show that the surface roughness and cutting forces increase with the feed rate, whereas their variations are not uniform when changing the cutting speed. Generally, a lower surface roughness was achieved by using a lower cutting feed rate (0.063 mm/rev) and higher cutting speeds (250–500 m/min). It was also found that the cutting forces and surface roughness vary significantly and nonlinearly with the lead angle of the cutting tool with respect to the surface.

Effect of surface density and fiber length on the porosity and permeability of nonwoven flax reinforcement

This paper presents an experimental study and modeling of the influence of surface density and fiber length on the permeability of novel nonwoven flax fiber manufactured by the paper making process. Firstly, the relation between surface density, fiber lengths and pore size distribution measured with a porometer capillary instrument is reported in this study. The results show that higher surface density gives a denser fibrous network with a low porosity rate and longer fiber decreases the total number of fibers and increases the pore size for a given surface density. A liquid permeability study was then carried out to identify the impact of surface density, short fiber length and fiber volume fraction on in-plane impregnation of the reinforcement. Permeability was found to be inversely proportional to the reinforcement of surface density. In contrast, an increase of the fiber length increases the in-plane permeability of the reinforcement. Finally, a mathematical modeling is proposed to predict the permeability behavior of these innovative natural fiber webs.

Machining analysis of unidirectional and bi-directional flax-epoxy composite laminates

Natural fibers, and more particularly, flax fibers, have a considerable potential as replacements for synthetic fibers. These fibers are of significant economic and environmental interest because they are natural products, are biodegradable, and unlike synthetic fibers, are entirely recyclable. They are also less expensive than synthetic fibers, less abrasive for machining, and their specific properties (strength-to-weight ratio) are comparable to those of glass fibers. Consequently, they thus provide economic and environmental benefits for companies. Unfortunately, machining knowledge with respect to this kind of material is low, and research in this domain has barely begun. The objective of this study is to describe the machinability of unidirectional and bidirectional flax/epoxy composites and to analyze the influence of cutting parameters and fiber orientation on cutting forces and surface finish. Milling tests were performed on unidirectional composite laminates with two different tools. The results show that the surface finish and cutting forces depend largely on the feed rate, and to a lesser extent, on the cutting speed. The PCD cutting tool, with a zero helix angle, showed the best performances as compared to the CVD cutting tool, which had a different geometry. The former provided a better surface finish, a lower delamination factor, and lower cutting forces. The material was found to be easy to machine and low abrasive, since no tool wear was observed following the cutting tests. Finally, it was found that an intermediate feed rate value and a high cutting speed were the best of all parameters tested for achieving a low cutting force level, low surface roughness, and high throughput.

Effet de l’acétylation en masse sur la mouillabilité et la stabilité thermique des fibres lignocellulosiques

RÉSUMÉ. L’acétylation est l’un des traitements chimiques les plus répandus qui visent l’amélioration de l’affinité des fibres lignocellulosiques avec les matrices polymériques dans les matériaux composites. Dans cette étude, des fibres de lin et des pâtes de bois (pâte kraft blanchie et pâte thermomécanique) ont été acétylées dans des conditions respectueuses de l’environnement et convenables pour un usage industriel. Ces fibres ont fait l’objet d’une étude concernant leur stabilité thermique. Le passage de l’hydrophilie à l’hydrophobie des fibres a été étudié par la mesure de l’angle de contact que forme une goutte d’eau avec la surface des fibres. La mouillabilité des fibres à la résine époxy a été également évaluée pour confirmer l’amélioration de l’affinité des fibres acétylées envers la matrice époxy. Les résultats ont montré que l’hydrophilie des fibres diminue avec la durée de la réaction et cette évolution devient de plus en plus faible à des taux d’acétylation élevés. Il en ressort que les fibres acétylées peuvent concurrencer les renforts d’origine fossile dans les matériaux composites.

Experimental Investigation to Study Cutting Temperature During Milling of Unidirectional Carbon Fiber Reinforced Plastic

The surface machining of Carbon Fiber Reinforced Plastics (CFRP) materials is a challenging process, given the heterogeneity and anisotropic nature of these composites, which, combined with the abrasiveness of the fibers involved, can produce some surface damage and extensive tool wear. The cutting temperature is one of the most important factors associated with the tool wear rate and machinability of these materials, which are also affected by the mechanical and thermal properties of the work material and the cutting conditions. In this work, the cutting temperature, forces and surface roughness were measured under different cutting conditions during the ball-end milling of unidirectional CFRP. Cutting speeds ranging from 200 to 350 m/min, a feed rate of 0.063 mm/rev, fiber orientation of (the angle between carbon fibers and feed direction) 0, 45, 90 and 135 degrees, and a 0.5 mm depth of cut were used. The results show that the cutting speed and fiber orientation have a significant influence on the cutting temperature and cutting force. The maximum and minimum cutting forces and temperature were achieved for fiber orientations of 90 and 0 degrees, respectively.Copyright