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In the hemp industry, retting is considered as an upstream processing treatment that facilitates the decortication of fibres in the central woody part of the stem. This treatment is currently carried out empirically in the fields, and leads to variability in the color, (micro)structure and intrinsic properties (thermal properties) of hemp fibers. The present study aims to compare unretted and retted hemp fibres harvested at the end of flowering. The results show that retting induces a change in the color of fibres from light green to dark gray due to the activity of the microbial community at the stem surface. A separation of the fibre bundles into elementary fibres occurs with the degradation of the cementing compounds present in the middle lamella. The cellulose and its crystallinity degree increased from 68 to 75 % and 85 to 89 %, respectively, with a removal of non-cellulosic materials, which leads to an improvement of the thermal stability for the retted fibres. [ABSTRACT FROM AUTHOR]

The raw earth is a natural material originating from the slow decomposition of rocks and stones. It can be used as a construction material as cob, daub, wattle, adobe, moulded bricks, rammed earth or compressed earth blocks. The use of a specific technique depends on the vernacular habits and also on the climate to which the building will be submitted or on the intrinsic properties of the earth. In this paper, we study the thermal and mechanical properties of compressed earth blocks (CEB) made of raw earth from Benin. In order to improve the mechanical properties of this brittle material, especially the tensile stress, kenaf fibers are incorporated into the mix. To determine the influence of the fibers on the various properties of CEB, the fiber content and the fiber length was varied. The results show a strong influence of these parameters on the porosity and as a consequence on the thermal and mechanical properties (compressive and tensile strengths). The increase in the porosity of the material yields a decrease in the mechanical strengths whatever the fiber content, except for long fibers. This seems to demonstrate combined effects of the porosity decrease and of the resistance to traction efforts due to the fibers. The addition of fibers also induces a decrease in the thermal conductivity of the material mainly due to the increase in the porosity. [ABSTRACT FROM AUTHOR]

The laser filament winding of preimpregnated thermoplastic tapes requires a multiphysical analysis, leading to the control of transformation parameters. Such an analysis is generally carried out by considering the raw material, the tape, as a "standard material". Consequently, conclusions can be biased due to the material variability, which presents at least a natural variability, at worst local or repeated defects. Therefore, in the present work, the subject under study is the thermal behavior of the tape, independently of the manufacturing conditions. The detected thermal irregularities are then put into perspective with the irregularities of the material, such as thickness variations or porosities. [ABSTRACT FROM AUTHOR]

This study deals with thermal and mechanical modelling of plasma sprayed zirconia coatings on stainless steel substrates, with a NiCrAlY bond coat. Applications concern thermal barrier coatings (TBC). Typically a coating of some hundreds micrometers induces a decrease of some hundreds degrees on the substrate temperature following the thermal flux. NiCrAlY permits to regularise the gap of the dilatation coefficients between the substrate and the ceramic. The NiCrAlY improves the adhesion of the coatings by providing a transition between the level of residual stresses in the three layers. A numerical model is developed and integrated to the industrial code ABAQUS based on finite elements approximation to simulates these behaviours under a parametric study. [ABSTRACT FROM AUTHOR]

The applied thermo-mechanical loading during cutting process leads to an important tool failure especially when machining is effected on refractory super-alloys such as titanium and/or nickel based-alloys. Heat removal generated by tool/workpiece friction plays an important role in preserving the structural integrity of the cutting tool. Efficient heat removal in machining depends solely on the thermal properties of the tool and on their evolution with temperature and mechanical parameters (strain, strain rate, etc.). In the present work, the effect of these thermal properties on the produced wear during the machining of refractory alloys is particularly investigated. Finite-Element Analysis (FEA) and SEM-imagery were used to map the thermal conductivity within the affected tool zone. The results indicate that depending on the temperature rise, the tool-tip might undergo a severe drop in thermal conduction. This drop may locally restrict the ability of the tool material to dissipate the applied thermal load. This may nucleate thermally congested clusters within the tool-tip where the material completely loses the ability to transport heat. Thermal congestion renders an energetically active zone where the thermal energy available may be used to activate wear through different mechanisms. It is also found that the immediate layer under the surface of the tool tip is important to enhance the ability of the tool material to dissipate the thermal loads. The results also highlight the importance of matching the temperature dependant properties of the different coating layers in order to enhance delamination resistance. [ABSTRACT FROM AUTHOR]

Abstract: We propose an analytical and numerical study of the combined action of the thermodiffusion and the convection in a binary mixture. The combination of these two phenomena is called thermogravitational diffusion. We are interested in quantifying the separation in a horizontal parallelepipedic cavity filled with a binary mixture and subjected to a constant horizontal temperature gradient on the two horizontal walls, the other walls being thermally insulated and impermeable. This new procedure is different from the classical one where the cavity is vertical and differentially heated on the two vertical walls. To cite this article: B. Elhajjar et al., C. R. Mecanique 334 (2006). [Copyright &y& Elsevier]

The prediction of concrete strength has become a major concern that is forcing the construction industry to look closely at determining the appropriate time when to strip the form work or to apply prestress forces to new concrete. Normal concrete has different constitutions and can be subjected to different curing methods depending on the means available. Its characteristics are defined by the presence of mineral additives used to improve its efficiency. This has led us to establish a work plan to predict the strength of slag concrete, tested at different temperatures, from the data obtained from some control specimens of normal concrete, made only from clinker and subjected to a constant temperature of 20°C. The slag material was obtained from El-Hadjar (Algeria).Key words: slag, activation, temperature, finesse, thermal treatment, prediction, equivalent time, mortar, compression, cement, additives.La prévision de la résistance des bétons d'aujourd'hui est devenue une préoccupation majeure poussant les promoteurs de la construction à s'y intéresser de plus en plus pour prévoir le décoffrage ou la mise en précontrainte à un âge approprié. Les bétons actuels possèdent une composition différente des bétons d'hier caractérisée par la présence de certains ajouts minéraux pour améliorer ses performances et un mode de cure variant selon les moyens disponibles. Ceci nous a conduit à établir un organigramme de prévision de la résistance en compression des bétons au laitier d'El-Hadjar subissant un historique de température variable, à partir d'un béton de référence confectionné uniquement avec du clinker et conservé sous une température constante de 20°C.Mots clés : laitier, activation, température, finesse, traitement thermique, prévision, temps équivalent, mortier, compression, ciment, ajouts. [ABSTRACT FROM AUTHOR]