Additive manufacturing with cement-based materials needs sound approaches for the direct, seamless integration of reinforcement into structural and non-structural elements during their fabrication. ...Mineral-impregnated Carbon-Fibre (MCF) composites represent a new type of non-corrosive reinforcement that offers great potential in this regard. MCF not only exhibits high performance with respect to its mechanical characteristics and durability, but it also can be processed and shaped easily in the fresh state and, what is more, automated. This article describes different concepts for the continuous, fully automated integration of MCF reinforcement into 3D concrete printing based on layered extrusion. Moreover, for one of the approaches presented and discussed, namely 3D concrete printing with MCF supply from a continuous, stationary impregnation line and deposition of MCF between concrete filaments, a feasibility study was performed using a gantry 3D printer. Small-scale walls were printed and eventually used for the production of specimens for mechanical testing. Three-point bend tests performed on two different beam geometries showed a significant enhancement of both flexural strength and, more especially, deformability of the specimens reinforced with MCF in comparison to the specimens made of plain concrete.
In this study, the strain rate sensitivity of five different thermoplastic polymers processed via Fused Filament Fabrication (FFF) Additive Manufacturing (AM) is reported. Namely, Polylactic Acid ...(PLA), Acrylonitrile-Butadiene-Styrene (ABS), Polyethylene Terephthalate Glycol (PETG), Polyamide 6 (PA6), and Polypropylene (PP) were thoroughly investigated under static tensile loading conditions at different strain rates. Strain rates have been selected representing the most common applications of polymeric materials manufactured by Three-Dimensional (3D) Printing. Each polymer was exposed to five different strain rates in order to elucidate the dependency and sensitivity of the tensile properties, i.e., stiffness, strength, and toughness on the applied strain rate. Scanning Electron Microscopy (SEM) was employed to investigate the 3D printed samples' fractured surfaces, as a means to derive important information regarding the fracture process, the type of fracture (brittle or ductile), as well as correlate the fractured surface characteristics with the mechanical response under certain strain rate conditions. An Expectation-Maximization (EM) analysis was carried out. Finally, a comparison is presented calculating the strain rate sensitivity index "m" and toughness of all materials at the different applied strain rates.
Mineral-impregnated carbon fiber composites (MCF) constitute a new type of reinforcement for construction. While inheriting the advantages of existing carbon fiber reinforcements, which are composite ...materials made of carbon filaments embedded in a thermoplastic or thermosetting matrix, MCF surpass the limitations of such polymer-impregnated types. More particularly, mineral impregnation considerably improves the performance of the reinforcement at elevated temperatures, enhances its bond to the concrete matrix, and increases technological flexibility, especially with respect to emerging automated production approaches. The article at hand presents the technology for continuous impregnation of carbon yarns with appropriately chosen fine mineral binder suspensions. Several examples for the automated manufacturing of reinforcement systems made of this new composite material are provided: one-dimensional elements such as bars and strips, two-dimensional reinforcements in the form of mats, and three-dimensional cases as examples of reinforcements for a balcony and shell elements. Furthermore, an outlook on introducing the novel reinforcement into highly automated, additive construction technologies is given.
•Mineral-impregnated, carbon fiber composite (MCF) is a new reinforcement material.•MCF exhibits excellent temperature resistance, durability and bond to concrete.•MCF opens numerous opportunities for highly automated and digitized technologies.•One-, two- and three-dimensional reinforcement elements can be produced.•Challenges with respect to up-scaling and full automation are discussed.
In this study, an industrially scalable method is reported for the fabrication of polylactic acid (PLA)/silver nanoparticle (AgNP) nanocomposite filaments by an in-situ reduction reactive melt mixing ...method. The PLA/AgNP nanocomposite filaments have been produced initially reducing silver ions (Ag+) arising from silver nitrate (AgNO3) precursor mixed in the polymer melt to elemental silver (Ag0) nanoparticles, utilizing polyethylene glycol (PEG) or polyvinyl pyrrolidone (PVP), respectively, as macromolecular blend compound reducing agents. PEG and PVP were added at various concentrations, to the PLA matrix. The PLA/AgNP filaments have been used to manufacture 3D printed antimicrobial (AM) parts by Fused Filament Fabrication (FFF). The 3D printed PLA/AgNP parts exhibited significant AM properties examined by the reduction in Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria viability (%) experiments at 30, 60, and 120 min duration of contact (p < 0.05; p-value (p): probability). It could be envisaged that the 3D printed parts manufactured and tested herein mimic nature’s mechanism against bacteria and in terms of antimicrobial properties, contact angle for their anti-adhesive behavior and mechanical properties could create new avenues for the next generation of low-cost and on-demand additive manufacturing produced personal protective equipment (PPE) as well as healthcare and nosocomial antimicrobial equipment.
In order to enhance the mechanical performance of three-dimensional (3D) printed structures fabricated via commercially available fused filament fabrication (FFF) 3D printers, novel nanocomposite ...filaments were produced herein following a melt mixing process, and further 3D printed and characterized. Titanium Dioxide (TiO2) and Antimony (Sb) doped Tin Oxide (SnO2) nanoparticles (NPs), hereafter denoted as ATO, were selected as fillers for a polymeric acrylonitrile butadiene styrene (ABS) thermoplastic matrix at various weight % (wt%) concentrations. Tensile and flexural test specimens were 3D printed, according to international standards. It was proven that TiO2 filler enhanced the overall tensile strength by 7%, the flexure strength by 12%, and the micro-hardness by 6%, while for the ATO filler, the corresponding values were 9%, 13%, and 6% respectively, compared to unfilled ABS. Atomic force microscopy (AFM) revealed the size of TiO2 (40 ± 10 nm) and ATO (52 ± 11 nm) NPs. Raman spectroscopy was performed for the TiO2 and ATO NPs as well as for the 3D printed nanocomposites to verify the polymer structure and the incorporated TiO2 and ATO nanocrystallites in the polymer matrix. The scope of this work was to fabricate novel nanocomposite filaments using commercially available materials with enhanced overall mechanical properties that industry can benefit from.
The influence of fiber type on the mechanical behavior of high-strength strain-hardening cement-based composites (HS-SHCC) during and after exposure to elevated temperatures of up to 200 °C was ...investigated. The fibers under investigation were made of ultra-high molecular-weight polyethylene (UHMWPE), para-aramid-copolymer (Aramid) and as as-spun and high-modulus poly(p-phenylen-2,6-benzobisoxazol), i.e., PBO-AS and PBO-HM. Based on the considerably higher thermal stability of Aramid and PBO fibers in comparison to UHMWPE, the effect of elevated temperatures on the tensile behavior of SHCC made with Aramid and PBO was expected to be less pronounced. Nevertheless, the SHCC made with UHMWPE fiber yielded a significantly superior multiple cracking and pre-peak ductility up to 150 °C both during and after thermal exposure. At 105 °C, the SHCC reinforced with UHMWPE fiber yielded only a small reduction in tensile strength and a considerable increase in strain capacity. The composites made with Aramid and PBO fibers yielded a pronounced degradation in tensile strength and strain capacity already at 105 °C and a considerably weaker recovery of ductility when cooled down to the room temperature. At 200 °C all composites except those containing Aramid fiber exhibited no multiple cracking and brittle failure with dramatically reduced tensile strength.
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•The Aramid and poly(p-phenylen-2, 6-benzobisoxazol) PBO fibers show a high thermal resistance up to 200 °C.•As opposed to their mechanical strength, the crack-bridging of Aramid and PBO fibers vanishes at elevated temperatures;•Ultra-high molecular weight polyethylene fibers yield an enhanced crack-bridging behavior at 105 °C.•High-strength strain-hardening cement-based composites yield quasi-brittle behavior during and after exposure to 200 °C.
Jute fibers (JFs) coated with multiwall carbon nanotubes (MWCNTs) have been introduced in a natural rubber (NR) matrix creating a three-dimensional (3D) electrically conductive percolated network. ...The JF-CNT endowed electrical conductivity and thermoelectric properties to the final composites. CNT networks fully covered the fiber surfaces as shown by the corresponding scanning electron microscopy (SEM) analysis. NR/JF-CNT composites, at 10, 20 and 30 phr (parts per hundred gram of rubber) have been manufactured using a two-roll mixing process. The highest value of electrical conductivity (σ) was 81 S/m for the 30 phr composite. Thermoelectric measurements revealed slight differences in the Seebeck coefficient (S), while the highest power factor (PF) was 1.80 × 10−2 μW/m K−2 for the 30 phr loading. The micromechanical properties and electrical response of the composite’s conductive interface have been studied in peak force tapping quantitative nanomechanical (PFT QNM) and conductive atomic force microscopy (c-AFM) mode. The JF-CNT create an electrically percolated network at all fiber loadings endowing electrical and thermoelectric properties to the NR matrix, considered thus as promising thermoelectric stretchable materials.
Mineral-impregnated, carbon fiber composites (MCF) are a promising alternative to conventional concrete reinforcements. For the efficient industrial production of MCF, sufficient processing time for ...the impregnation suspension must be ensured. In the present investigation, a metakaolin-made geopolymer (GP) has been developed and tested for this purpose. The impregnation of carbon-fiber yarns was performed continuously and automated. Subsequently, the MCF were heat-treated at 75 °C to accelerate the reaction processes. The mechanical performance of MCF gradually increased in the advancement of the curing process from 2 to 8 h, which is attributed to the greater extent of geopolymerization. In such extended curing, thermogravimetric and microscopic analysis showed indeed a more “reacted” microstructure but also a higher content of voids. After heating for 8 h, the tensile strength and Young's modulus of MCF reached 2960 MPa and 259 GPa, respectively, when related to the yarn cross-sectional area.
The thermoelectric properties of conductive polymer composites consisting of a polycarbonate (PC) matrix loaded with different kinds of commercially available multi-walled carbon nanotubes (MWCNTs) ...have been examined. The PC/MWCNT composites were prepared by melt-mixing using a small-scale compounder. Unfunctionalized, as well as carboxyl (–COOH) and hydroxyl (–OH) modified MWCNTs were incorporated into the PC matrix at a constant amount of 2.5wt.%, which is a concentration above the electrical percolation threshold. The amount of MWCNTs was kept low to understand the fundamental aspects of the physical properties and their correlation to the composite morphology. The results suggest that different functional groups on the surface of MWCNTs can have an impact on the thermoelectric values and the conductivity of the composites, measured at room temperature. The highest Seebeck coefficient (S) was found for the composite containing carboxyl functionalized MWCNTs (11.3μV/K). In specific, an increase of the Seebeck coefficient was found with an increased oxygen content of MWCNTs. It is believed that these thermoelectric figure of merit values are still too low for commercial applications; however, they can be enhanced by increasing the amount of conducting fillers and improvement of dispersion in the polymer matrix.
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