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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Stainless steel wires reinforced ultra-high performance concrete for self-moderating and self-sensing temperature deformations

Ding, S., Dong, S., Ashour, Ashraf, Wang, X., Han, B. 26 July 2024 (has links)
Yes / The development of self-moderating and self-sensing concrete composites with high and stable thermal/electrical conductivity is essential to mitigate and monitor the temperature deformation behaviours (TDB) of engineering infrastructures such as highways, bridge pavements, airstrips and ports. Owing to the micron-scale diameter and high aspect ratio, stainless steel wires (SSWs) can establish a comprehensive and extensive thermal/electrical, as well as reinforcing, three-dimensional network within the concrete matrix, even at a low content. This paper thus investigated the TDB self-moderating and self-sensing performances of SSWs enhanced ultra-high performance concrete (UHPC). The main experiments were carried out on SSWs enhanced UHPC slabs, measuring 250 mm×225 mm×16 mm. The volume contents of SSWs studied were 0 %, 0.5 vol%, 1.0 vol% and 1.5 vol%. The TDB self-moderating and self-sensing experiments were carried out under different conditions, including indoor and outdoor environments. Such composites showed effective and highly stable capabilities in reducing the temperature difference and diminishing the strain of pavement slabs under different environmental conditions. Compared with the UHPC without SSWs, UHPC with 1.5 vol% of SSWs can reduce the temperature difference by 7.4 °C (39.4 %) when being heated from 21.6 °C to 50 °C, thus, reducing the maximum tensile/compressive strains by 83.1 %/82.2 %, and the tensile/compressive stresses by 70.8 %/82.0 %. At a heating rate of 67.1 °C/min, incorporating 1.5 vol% of SSWs results in significant reductions in both vertical displacement and stress, amounting to 98.6 % and 89.6 %, respectively. The 1.5 vol% SSWs reinforced UHPC slab also suppressed 25.0 % of temperature difference, 76.6 % of strain and 70.7 % of stress in scorching outdoor environments. The TDB of SSWs reinforced UHPC can be real-timely reflected by monitoring the quick and small-scale resistance fluctuations, and the fractional changes in resistivity can reach 5.24 % with a response time of 0.23 s. The self-moderating and self-sensing performances of such composites remained stable after repeated heating experiments, thus suggesting its potential for promising applications in engineering infrastructures which are susceptible to deformation under high-temperature conditions. / National Science Foundation of China (Grant Nos. 51908103 , 51978127 , and 52178188 ), and the Major Science and Technology Research Project of the China Building Materials Federation ( 2023JBGS10-02 ). / The full text will be available at the end of the publisher's embargo: 13th May 2025
2

Revêtements architecturés de Ti, TiN et TiO élaborés par pulvérisation cathodique au défilé sur des fils en acier inoxydable : relation entre la composition chimique, la microstructure et les propriétés d'usage / Architectured Ti-based coatings grown by PVD on moving stainless steel wires : relationship between chemical composition, microstructure and properties

Grosso, Stéphane 17 November 2017 (has links)
Cette thèse porte sur la fonctionnalisation de fils en acier inoxydable via des revêtements colorés base titane, élaborés par pulvérisation cathodique avec un magnétron cylindrique. Ce travail s’intéresse à la caractérisation chimique, morpho-structurale et à l’évaluation de la durabilité mécano-chimique des fils revêtus.Premièrement, la vitesse de dépôt et la composition chimique des films sont déterminées dans des conditions statiques. Les hétérogénéités du plasma dans la cathode sont démontrées et reliées aux paramètres tels que la puissance, la pression et la polarisation d’anodes auxiliaires.Les dépôts monocouches de Ti, TiN et TiOx sont ensuite élaborés en continu. La relation entre la couleur du TiN et sa composition chimique est établie. La couleur dorée est obtenue pour des films stœchiométriques contenant peu d’oxygène (< 5 %at.). Les microstructures sont caractérisées par MET-ASTAR et des cartographies d’orientation sont dressées à l’échelle nanométrique. Tandis que les dépôts de TiN sont colonnaires avec une texturation selon <111>, les grains des films de Ti sont plutôt équiaxes et orientés selon <0001>. Pour une température d’élaboration de 650 °C, les éléments du substrat diffusent dans les films et mènent à la formation de phases de Laves. Les dépôts de TiOx, élaborés en mode métallique, présentent des couleurs d’interférence et une composition proche du monoxyde. Les surfaces revêtues de TiN ont une résistance à la corrosion élevée semblable à l’acier inoxydable 316L, contrairement aux fils revêtus de Ti et TiOx. La ténacité et l’énergie d’adhérence des revêtements sont déterminées par traction in-situ sous MEB : Ti et TiN sont particulièrement adhérents au substrat contrairement à TiOx.Enfin, les dépôts sont architecturés avec l’ajout d’un dépôt de titane entre le substrat et le revêtement céramique. Ainsi, l’adhérence du film Ti-TiOx est largement augmentée par rapport au monocouche TiOx (5 à 200 J/m2). Enfin, les études microstructurales et électrochimiques montrent qu’un paramètre clef de la résistance à la corrosion est la présence de porosité ouverte dans les revêtements. / This thesis treats of the functionalization of stainless steel wires with colored Ti-based coatings, grown by PVD with a cylindrical magnetron, their chemical and morpho-structural characterization, and the evaluation of the chemico-mechanical durability of the coated wires.First, the deposition rate and the chemical composition of the films are determined under static conditions. Cathode plasma heterogeneities are demonstrated and related to parameters such as power, pressure and polarization of auxiliary anodes.Then, Ti, TiN and TiOx monolayer coatings are grown continuously. The relationship between the color of TiN and its chemical composition is established and golden color is obtained for stoichiometric films with low oxygen content (<5% at.). Microstructures are studied with TEM-ASTAR and orientation maps are obtained with a nanometric resolution. While TiN coatings are columnar with <111> texture, Ti grains are rather equiaxed and <0001> oriented. With a 650 ° C substrate temperature, substrate elements diffuse into the films which results in Laves phase formation. TiOx is grown in metallic mode, presents interference colors and a composition close to monoxide. TiN coated surfaces display high corrosion resistance similar to 316L stainless steel, unlike Ti and TiOx coated wires. The toughness and the adhesion energy of the coatings are determined by SEM in-situ tensile tests: Ti and TiN are particularly adherent to the substrate in contrast to TiOx.Finally, coatings are architectured with the addition of a titanium interlayer between the substrate and the ceramic coating. Thus, Ti-TiOx film adhesion is greatly superior compared to the TiOx monolayer (5 to 200 J/m2). Finally, microstructural and electrochemical studies show that a key parameter of corrosion resistance is the presence of open porosity in the coatings.

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