Fabrication de structures tridimensionnelles de nanocomposites polymères chargés de nanotubes de carbone à simple paroi

Nanotubes de carbone -- Nanocomposites pour les applications mécaniques -- Nanocomposites pour les applications électriques -- Intégration -- Techniques de fabrication -- Démarche, organisation et cohérence des articles -- Préparation and mechanical characterization of laser ablated single-walled carbon-nanotubes/polyurethane nanocomposite microbeams -- Three-dimensional micro structured nanocomposite beams by microfluidic infiltration -- Ultravaiolet-assisted direct-write fabrication of carbon nanotube/polymer nacocomposite micro-coils

Manufacturing of braided thermoplastic composites with commingled fibers

Through this work, an investigation on thermoplastic composites manufactured with braided commingled fibers is performed. Thermoplastic composites have the potential for complex shape part manufacturing with a cost-effective perspective. However they present a manufacturing challenge because of the high melt viscosity of their matrices. Among the many solutions to this problem commingled yarns present a promising avenue. The commingled yarn studied here is a carbon/nylon yarn from Schappes Techniques France. Braiding is used to manufacture preforms from this yarn. Bi-axial braiding is described with the mathematical relations regulating the process. The machine available in the lab has been calibrated and seven fabrics have been produced with seven different braiding conditions to explore the preforming method. The fabrics have been consolidated using compression molding. A model to predict the final thickness of the consolidated braid is proposed. The evaluation of the quality of the consolidation was performed using a constituent content method and a qualitative observation by microscopy. Both methods were developed in the scope of this work. Flexural and tensile mechanical properties of the consolidated laminates are tested. The tensile modulus data are compared to a mathematical model using the classical lamination theory

Fiber-level bi-axial braid simulation for braid-trusion

Braid-trusion is a manufacturing process using a braided textile preform that is pulled into a pultrusion die. This process produces constant cross-section beams having reinforcement fibers oriented along the braid angle. The bi-axial braids are made from commingled yarns mixing carbon fibers and thermoplastic filaments. The bi-axial braid architecture is locked by the contacts between the bulky carbon/thermoplastic yarns. During pultrusion, the thermoplastic filaments melt. At this moment, the processing tensile loads adjust the braid architecture. The braid angle and the braid diameter reduces by reaching another locked state. This second locked state is driven by contacts between carbon yarns. The aim of this research is to model the braid deformation at the fiber scale using a non-linear finite element method. The model geometry is set up by the helix sinusoidal relations of the yarns path along a braid pitch. The braid large deformation is precisely modeled via a bundle of three-dimensional beam elements. The intertwined fibers contacts are modeled within a dynamic explicit solution. The model is validated with CT Scans of carbon fiber braids. This work will help the design of braid architecture for braid-trusion manufacturing

3D Printing Of Metallic Structures From A Green Ink

A green metallic ink is developed for 3D printing of metallic structures featuring high mechanical and electrical performances. The metallic ink consists of steel micro powders and a water-based chitosan/acetic acid polymer solution which replaces the previously used toxic polylactic acid (PLA)/dichloromethane (DCM) polymer solution. The optimized ink is printed at room temperature to build a metal/polymer hybrid structure. While printing, a fan is used to blow air over the ink filament upon extrusion to accelerate the solvent evaporation and shorten the solidification time, which significantly reduces the sagging and deformation. After a drying period at ambient conditions, the as-printed structure is then thermally treated using a furnace. The polymer binder is decomposed and the metal powders are sintered, resulting in a strong metallic structure. Melted copper is infiltrated into the sintered structure to achieve a fully dense metal/metal hybrid structure. The sintered structure exhibits high stiffness (205 GPa), electrical conductivity (9 × 105 S/m) and low filament porosity (7%)

Processing parameters investigation for the fabrication of self-supported and freeform polymeric microstructures using ultraviolet-assisted three-dimensional printing

The ultraviolet-assisted 3D printing (UV-3DP) was used to manufacture photopolymer-based microdevices with 3D self-supported and freeform features. The UV-3DP technique consists of the robotized deposition of extruded filaments, which are rapidly photopolymerized under UV illumination during the deposition process. This paper systematically studies the processing parameters of the UV-3DP technique using two photo-curable polymers and their associated nanocomposite materials. The main processing parameters including materials’ rheological behavior, deposition speed and extrusion pressure, and UV illumination conditions were thoroughly investigated. A processing map was then defined in order to help choosing the proper parameters for the UV-3D printing of microstructures with various geometries. Compared to self-supported features, the accurate fabrication of 3D freeform structures was found to take place in a narrower processing region since a higher rigidity of the extruded filament was required for structural stability. Finally, various 3D self-supported and freeform microstructures with high potential in micro electromechanical systems, micro-systems and organic electronics were fabricated to show the capability of the technique

Environment-friendly and reusable ink for 3D printing of metallic structures

ABSTRACT: There is an increasing need for 3D printing of metallic structures in a green and cost-effective way. Here, an environment-friendly and reusable metallic ink was developed for an economical metal 3D printing method. The metallic ink is composed of steel micro powders, a biodegradable polymer: chitosan, acetic acid and deionized water. The metal 3D printing method consists of: (i) 3D printing of metallic structures using the metallic ink at room temperature, (ii) thermal treatments on the as-printed structures that decompose the polymer binder and sinter the steel powders, and (iii) an optional step: infiltrating melted copper into the sintered structures to achieve fully dense metal/metal hybrid structures. We demonstrate that any incorrectly built as-printed structures and scrap materials can be recycled and reused for 3D printing by dissolving them again in acetic acid. The fabricated structures after copper infiltration feature a low filament porosity of 1.0% which enables high properties such as an electrical conductivity of 1.3 × 106 S/m and a Young's modulus of 160 GPa. The metallic ink can be used for the 3D printing of high performance metallic structures while demonstrating a low environmental impact and a very effective utilization of metallic materials

Preparation and mechanical characterization of laser ablated single-walled carbon-nanotubes/polyurethane nanocomposite microbeams

We report on the preparation of nanocomposites consisting of laser synthesized single-walled carbon nanotubes (C-SWNTs) reinforcing a polyurethane. Prior to their incorporation into the polymer matrix, the C-SWNTs were purified, and characterized by means of various techniques. The purification in nitric acid added carboxylic groups to the C-SWNTs. A procedure to properly disperse the nanomaterials in the polymer was developed involving high shear mixing using a three-roll mill and a non-covalent functionalization of the nanotubes by zinc protoporphyrin IX molecule. The incorporation of the C-SWNTs into the resin led to an increase of the viscosity and the apparition of a slight shear-thinning behavior. A further increase of the shear-thinning behavior using fumed silica particles enabled the direct-write fabrication of microbeams. Mechanical characterization revealed significant increase in both strength (by ∼64%) and modulus (by more than 15 times). These mechanical enhancements are believed to be a consequence of the successful covalent and the non-covalent functionalizations of the nanotubes

Three-dimensional micro structured nanocomposite beams by microfluidic infiltration

Three-dimensional (3D) micro structured beams reinforced with a single-walled carbon nanotube (C-SWNT)/polymer nanocomposite were fabricated using an approach based on the infiltration of 3D microfluidic networks. The 3D microfluidic network was first fabricated by the direct-write assembly method, which consists of the robotized deposition of fugitive ink filaments on an epoxy substrate, forming thereby a 3D micro structured scaffold. After encapsulating the 3D micro-scaffold structure with an epoxy resin, the fugitive ink was liquefied and removed, resulting in a 3D network of interconnected microchannels. This microfluidic network was then infiltrated by a polymer loaded with C-SWNTs and subsequently cured. Prior to their incorporation in the polymer matrix, the UV-laser synthesized C-SWNTs were purified, functionalized and dispersed into the matrix using a three-roll mixing mill. The final samples consist of rectangular beams having a complex 3D skeleton structure of C-SWNT/polymer nanocomposite fibers, adapted to offer better performance under flexural solicitation. Dynamic mechanical analysis in flexion showed an increase of 12.5% in the storage modulus compared to the resin infiltrated beams. The nanocomposite infiltration of microfluidic networks demonstrated here opens new prospects for the achievement of 3D reinforced micro structures