Analysis of the Mechanical Behavior of Wood and Welded Wood under Tensile–Shear Loads Using a Modified Arcan Device

Abstract

The aim of this work was to analyze the possibility of using a modified Arcan device to characterize the mechanical behavior, under tensile–shear loads, of wood and of wood assemblies obtained using friction welding without any adhesive. This process is interesting as only friction energy is used to assemble the two pieces of wood; thus, the process is characterized by low environmental impact and by easier recycling at the end of the product’s life. For this assembly technique to become widespread in industry, it is necessary to develop numerical tools in order to predict the behavior of such assemblies under complex loads. Thus, it is also necessary to obtain a large data base of experimental results under various tensile–shear loads, in order to analyze the multi-axial mechanical behavior of such welded assemblies. However, few experimental devices have been proposed in the literature, and furthermore, very few papers in the literature analyze the complex mechanical behavior of wood. This paper describes the use of a modified Arcan test to analyze the behavior of wooden blocks and their welded assemblies. The stress state in the middle of the specimens used was not homogenous and, thus, finite element simulations were required to determine the stress distributions. These simulations were possible as the load transmitted by the tensile loading machine was known. Some experimental results are presented in the case of beech wood in a transversal direction.     

Strain–Stress Formation During Stationary and Intermittent Drying of Deformable Media

The goal of this work is to study the effect of different drying conditions on the induced stresses within deformable media, the drying kinetics, and the energy consumption. A comparison between stationary and intermittent drying with periodically changing air temperature was performed. A theoretical formulation of the coupled heat, mass, and momentum transfers in saturated porous media was established. The model is based on the averaging theory. The thermo-hydro-mechanical coupling was closed using the effective stress theory of Terzaghi. In this approach, the viscoelastic behavior of the medium was considered. A bi-dimensional-shaped bentonite sample was used for numerical tests. The evolution of drying kinetics and stresses within the material during drying at constant and intermittent conditions was presented. It was observed that a non-stationary drying with smaller period applied at the end of the constant drying rate phase has the best effects on the product quality and energy gain without considerably extending the drying time.     

Design of Solar–Dehumidification Wood Drying Kiln Characterized by High Capacity and Temperature

ABSTRACT

Solar–;dehumidification wood drying kilns attract more and more interest due to their energy saving characteristics. However. such dryers are only available for small effective drying volume capacities. less than 30 m³, and for low drying temperature under 65 °C, for Chinese domestic products. In fact, wood drying kilns over 60 m³and high drying temperatures upto 95 °C or even higher are commonly desired from economic and process technology points o f view. For instance, if the drying temperature is below 60 °C. a long drying period will result in high operational costs and may also cause mould as well colour changes on the lumber surface. It is also known that the anti- decay ability of the seasoned lumber is lhus reduced. As such. the design of the solar–dehumidification wood drying kiln with an effective drying volume capacity of 60 m³ and a drying temperature upto 95 ⁰C was made. Two compression processes for dehumidification and heat pump systems were adopted. The refrigerant of R1⁽²⁾. which has low RODP and RGE, was utilized as the actuating medium. The values of COP. PER and SMER were 4.42. 1.19 and 3.08 kg ( H20) /( kWh) for the dehumidification system. The valucs of COP and PER were 3.05 and 0.824 for the heat pump (heat supply) system. The averaged total COP and PER over the both were 3.74 and 1.01 respectively.     

Strength and deformation of concrete with variable content of moisture at elevated temperature up to 90°C

It is known, that the change of mechanical properties of concrete due to elevated temperature is also influenced by the moisture content. This change was primarily studied for prestressed concrete reactor vessels (PCRV). Because a PCRV is a mass concrete structure, the results of this research cannot be transfered to slender members. To simulate drying conditions of the latter, specimens of differing initial moisture content were subject to elevated temperatures and defined climates. The results of tests reveal the differing influence of moisture on strength and modulus of elasticity. The compressive strength is partly increased, partly decreased as the moisture content grows. Tensile strength and modulus of elasticity are weakened by decreasing moisture. Also the thermal strain as function of type of aggregate and moisture content was studied. The changes are caused by the alteration of structure of cement stone and by microcracks due to incompatibility.     

Kinetic and thermodynamic studies on oxidative desulphurisation of organic sulphur from Indian coal at 50–150°C

This paper reports a relatively simple low-temperature non-isothermal oxidative desulphurisation of coal organic sulphur by weakening the CS bond using HgCl₂ solution to an inorganic sulphur-free high-sulphur Indian coal. When oxidised from 50°C to 150°C in air under normal atmospheric pressure, there is continuous decrease of organic sulphur content in the samples of the feed and Hg-treated coals. Desulphurisation is more in the Hg-treated coal (4.97–14.53 wt.%) than in the feed coal (3.72–10.93 wt.%). Kinetic study reveals that the oxidative desulphurisation process follows pseudo-first order kinetics and the rate constants have been found to be in the range (3.09–5.06)×10⁻⁵ s⁻¹ for feed coal and (4.19–6.80)×10⁻⁵ s⁻¹ for Hg-treated coal. The activation energies for the sulphur loss reaction in the oxidative desulphurisation process by using the pseudo-first order kinetic (feed coal: 2.21×10² J mol⁻¹; Hg-treated coal: 1.53×10² J mol⁻¹) have been found to be almost similar to those calculated by applying the Coats and Redfern's equation (feed coal: 2.19×10² J mol⁻¹; Hg-treated coal: 1.53×10² J mol⁻¹). However, the value is higher (feed coal: 3.50×10² J mol⁻¹; Hg-treated coal: 2.70×10² J mol⁻¹) when Horowitz and Metzger's equation is applied. The frequency factors computed by the pseudo-first order kinetics are very low and have been found to be 2.66×10⁻⁵ s⁻¹ for feed coal and 3.96×10⁻⁵ s⁻¹ for Hg-treated coal, suggesting very low rate of successful collisions for the formation of the activated complex. Evaluation of thermodynamic parameters viz., ΔH, ΔU, ΔS and ΔG, reveals that this oxidative desulphurisation process is non-spontaneous in nature and the degree of non-spontaneity of such a process in the feed coal is more relative to that of the Hg-treated coal.     

Microstructure and oxidation resistant of Si–NbSi2 coating on Nb substrate at 800°C and 1000°C

The Si–NbSi₂ composite coating with a smooth surface was successfully prepared on Nb substrate by hot dip silicon-plating (HDS) technology. The composite coating is composed of Si outer layer, NbSi₂ interlayer and Nb₅Si₃ interfacial layer. And the average surface roughness (RSa) and specific surface area growth rate (Sdr) are only 0.275 μm and 2.85%, respectively. The cyclic oxidation test shows that the Si–NbSi₂ composite coating has a very excellent oxidative resistance after oxidation at 800 °C for different times. After oxidation for 40 h, the Δm/S and oxide layer thickness of the coating are only 3.72 mg/cm² and 8 μm, respectively. After oxidation at 1000 °C for 20 h, the coating surface is almost completely covered by a dense SiO₂ layer, the Δm/S and oxide layer thickness of the coating are 7.28 mg/cm² and 15 μm, respectively. The Si–NbSi₂ composite coating presents good self-healing ability and excellent oxidation resistance, which can significantly prolong the service life of bare Nb in oxidation environment.     

Improving the Cyclic-Oxidation Resistance of Ti3AlC2 at 550°C and 650°C by Preoxidation at 1100°C

Preoxidation of Ti₃AlC₂ at 1100°C for 2 h was conducted to improve its cyclic-oxidation resistance at the testing temperature of 550°C and 650°C in air. The cyclic oxidation of the preoxidized Ti₃AlC₂ was found to follow a parabolic rate law rather than the linear oxidation rate for that without preoxidation. Through the X-ray diffraction and SEM analysis, the remarkable improvement of the cyclic-oxidation resistance of preoxidation Ti₃AlC₂ is suggested due to the existence of protective α-Al₂O₃ layers formed during the preoxidation treatment, which inhibits the formation of amorphous Al₂O₃, which can result in larger thermal stress and stress-induced microcracks.     

Solvent Migration and Drying Phbnoubnon of Polymeric Blends of Ethylene-Propylbnb Random Copolymbr and Isotactic Polypropylbnb in the Prbsbncb of Monocyclic Aromatic Liquids at Tbwbraturbs Bbtukbn 25-70°C.

ABSTRACT

Solvent sorption and drying performance of engineering polymeric blends of ethylene–propylene random copolymer and isotactic polypropylene in the presence of aromatic liquid: has been studied in the temperature interval 25–70°C. The drying of the polymer is studied from the desorption and redesorption experiments. The present results indicate that the rate of solvent migration and the drying phenomenon is controlled by internal mass transfer of solvent molecules within the polymer matrix. A technique is developed to study the sorption (S) –desorption (D) – resorption (RS)–redesorption (RD) i.e., S–D–RS–RD of the polymer sheets. The S–D–RS–RD experiments are a convenient measure of knowing the continuous weight loss of the polymer during long–term solvent exposure.     

Fish Oil Supplementation During Lactation: Effects on Cognition and Behavior at 7 Years of Age

Early accumulation of n-3 long-chain PUFA (LCPUFA) in the brain may contribute to differences in later cognitive abilities. In this study, our objective was to examine whether fish oil (FO) supplementation during lactation affects processing speed, working memory, inhibitory control, and socioemotional development at 7 years. Danish mothers (n = 122) were randomized to FO [1.5 g/d n-3 LCPUFA] or olive oil (OO) supplementation during the first 4 months of lactation. The trial also included a high-fish intake (HFI) reference group (n = 53). Ninety-eight children were followed-up with an assessment of processing speed, an age-appropriate Stroop task, and the Strength and Difficulties Questionnaire at 7 year. A group effect of the intervention (FO vs. OO) was found in prosocial behavior scores; this negative effect was carried by the boys. Exploratory analyses including all participants revealed the speed of processing scores were predicted by maternal n-3 LCPUFA intake during the intervention period (negative relation) and maternal education (positive relation). Stroop scores indicative of working memory and inhibitory control were predicted by infant erythrocyte DHA status at 4 months of age (negative relation). Early fish oil supplementation may have a negative effect on later cognitive abilities. Speed of processing and inhibitory control/working memory are differentially affected, with speed of processing showing effects of fish oil intake as a whole, whereas inhibitory control/working memory was related more specifically to DHA status.     

Experimental and Modeling Study During Freeze Drying of Aqueous tert-Butanol–Based Formulations in Vials

In this study, using COMSOL Multiphysics software, we set up a two-dimensional model for the sublimation step a frozen aqueous organic cosolvent tert-butyl alcohol (TBA) formulation without a dissolved active principal ingredient contained in 4-mL glass vials. This model, based on the hypothesis of a sublimation process mainly governed by the conductive heat transfer between the shelf and the sublimation front, allowed precise prediction of the sublimation kinetics and the sublimation front movement for different operating conditions. Next, this modeling was validated by many experimental runs under operating conditions corresponding to very low total gas pressures (5 to 50 Pa) and low shelf temperatures (0 to ?20°C) generally encountered during industrial freeze drying of thermosensible pharmaceuticals (vaccines, diagnostic proteins, serums, etc.).     

Characterization and properties of iron-incorporated gismondine prepared at 80°C

Iron-incorporated zeolites were successfully synthesized at a low temperature such as 80°C by choosing appropriate starting materials and characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), wide-angle X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), and magnetic susceptibility. ICP-AES showed␣that Fe component can be readily incorporated␣up to a maximum extent of Fe substitution, Fe/(Fe + Al) × 100 = 22.7%. XRD measurements suggested that the zeolites obtained have a crystal structure of gismondine type. The characterizations identified that the Fe component present in the products is all incorporated into the zeolite framework. The ammonia and water desorption profiles were compared for Fe-free and 22.7% Fe-zeolites ion-exchanged for NH₄⁺ by means of TG-MS and DSC. The ammonia desorption peak temperatures considerably shifted toward lower temperatures by the introduction of Fe, suggesting decreased solid acidity. DSC thermograms of the as-synthesized gismondines revealed that they do not contain free water (i.e., water not coordinated to cations) in the pores irrespective of the Fe content. The enhanced catalytic reactivity of the Fe-incorporated gismondines was also confirmed from the decomposition of hydrogen peroxide. An apparent activation energy of 43 kJ mol⁻¹ was obtained independent of the Fe contents in zeolites. This value was much lower than 70 kJ mol⁻¹ for the same reaction in the homogeneous solution containing iron alum as a reference sample.     

Strength retention in hot-pressed ZrB2–SiC composite after thermal cycling exposure in air at 1200 and 1400°C

The effect of thermal cycling exposure on room temperature flexural strength was examined in hot-pressed ZrB₂–SiC composite undergone cyclic heating-cooling test at 1200 and 1400°C in air for up to 1000 or 500 cycles. For the post-tested samples at 1200°C, the flexural strength of the composite initially increased and subsequently degraded with increase of number of thermal cycles (N). The strength retention displayed by the composite after N = 1000 cycles was approximately 80%. For the post-tested samples at 1400°C, however, the flexural strength decreased with increase of N. After N = 500 cycles, the strength retention was approximately 45%. The strength decrease was associated with the formation and coarsening of defects in the oxidized reactive layer and the delamination of the outermost thinner dense oxide layer.     

Organo-sulphur compounds and hydrocarbons of 65°–200°C distillates of Usino petroleum

• 1.1. The structural group composition of hydrocarbons and organosulphur compounds of a 65°-200°C distillate of Usino petroleum was studied by mass-spectrometry together with extraction, complex-formation and adsorption chromatography.
• 2.2. Organo-sulphur compounds of a low-boiling distillate are represented by saturated sulphides (0·59 wt.%), with the predominance of alkylthiamonocycloparaffins (0·43 wt.%) and thiophene compounds, mainly alkylthiopenes (0·09 wt.%) and alkylbenzothiophenes (0·05 wt.%). Thiaindane content in the distillate is 0·11 wt.%.
• 3.3. The main groupes of hydrocarbons in the distillate are: naphthenes (58·5% wt.%) mainly mono- and bicyclic, paraffins (37,4 wt.%) those with an isooctane structure (63%) and aromatics (5%).

     

Ablation behavior and mechanism of C/C–ZrC–SiC composites under an oxyacetylene torch at 3000 °C

C/C–ZrC–SiC composites with continuous ZrC–SiC ceramic matrix were prepared by a multistep technique of precursor infiltration and pyrolysis process. Ablation properties of the composites were tested under an oxyacetylene flame at 3000 °C for 120 s. The results show that the linear ablation rate of the composites was about an order lower than that of pure C/C and C/C–SiC composites as comparisons, and the mass of the C/C–ZrC–SiC composites increased after ablation. Three concentric ring regions with different coatings appeared on the surface of the ablated C/C–ZrC–SiC composites: (i) brim ablation region covered by a coating with layered structure including SiO₂ outer layer and ZrO₂–SiO₂ inner layer; (ii) transition ablation region, and (iii) center ablation region with molten ZrO₂ coating. Presence of these coatings which acted as an effective oxygen and heat barrier is the reason for the great ablation resistance of the composites.     

Phase relations of the MgO–SiO2–CrOx system at 1600°C in air and reducing atmospheres

The equilibrium phase relations of the MgO–SiO₂–CrO_x system were investigated at 1600°C in air and at pO₂ of 10^–10 to 10^–11 atm using a high-temperature isothermal equilibration technique followed by rapid quenching and direct phase composition analyses with electron probe X-ray microanalysis. Two-phase equilibria (liquid–cristobalite, liquid–spinel, liquid–corundum, and liquid–olivine) and three-phase equilibria (liquid–cristobalite–spinel, liquid–olivine–spinel, liquid–spinel–corundum, and cristobalite–spinel–corundum) were observed. The 1600°C isothermal sections at various oxygen partial pressures were constructed for the MgO–SiO₂–CrO_x system based on the experimentally determined liquid and solid compositions. Data from the literature and the predictions by FactSage and MTDATA software were compared with the present experimental results.     

Low-temperature reactive hot-pressing of Ta0.2Hf0.8C–SiC ceramics at 1700°C

Temperature above 2000°C and additional pressure is generally required to achieve the full densification of Ta_xHf_1−xC-based ceramics. This work proposed a novel method to fabricate dense Ta_0.2Hf_0.8C ceramics at relatively low temperature. Using a small amount of Si as a sintering aid, Ta_0.2Hf_0.8C was densified at 1700°C by reactive hot-pressing (RHP), with SiC formed in situ. Microstructure evolution mechanisms of the ceramics during RHP were investigated. The effect of silicon content on the densification and mechanical properties of the ceramics was revealed. It is indicated that the apparent porosity of the Ta_0.2Hf_0.8C–SiC ceramics was as low as 0.5%, whereas bending strength and fracture toughness of the ceramics were as high as ∼637 MPa and 6.7 MPa m^1/2, respectively, when the silicon content was 8 wt.%. This work provides a new idea for the low-temperature densification of Ta_xHf_1−xC and other ultrahigh temperature ceramics with high performance.     

Structural and physical properties of antibacterial Ag-doped nano-hydroxyapatite synthesized at 100°C

ABSTRACT: Synthesis of nanosized particle of Ag-doped hydroxyapatite with antibacterial properties is in the great interest in the development of new biomedical applications. In this article, we propose a method for synthesized the Ag-doped nanocrystalline hydroxyapatite. A silver-doped nanocrystalline hydroxyapatite was synthesized at 100°C in deionized water. Other phase or impurities were not observed. Silver-doped hydroxyapatite nanoparticles (Ag:HAp) were performed by setting the atomic ratio of Ag/[Ag + Ca] at 20% and [Ca + Ag]/P as 1.67. The X-ray diffraction studies demonstrate that powders made by co-precipitation at 100°C exhibit the apatite characteristics with good crystal structure and no new phase or impurity is found. The scanning electron microscopy (SEM) observations suggest that these materials present a little different morphology, which reveals a homogeneous aspect of the synthesized particles for all samples. The presence of calcium (Ca), phosphor (P), oxygen (O), and silver (Ag) in the Ag:HAp is confirmed by energy dispersive X-ray (EDAX) analysis. FT-IR and FT-Raman spectroscopies revealed that the presence of the various vibrational modes corresponds to phosphates and hydroxyl groups. The strain of Staphylococcus aureus was used to evaluate the antibacterial activity of the Ca10-xAgx(PO4)6(OH)2 (x = 0 and 0.2). In vitro bacterial adhesion study indicated a significant difference between HAp (x = 0) and Ag:HAp (x = 0.2). The Ag:Hap nanopowder showed higher inhibition.     

Incipient formation of zircon and hafnon during glass alteration at 90°C

Layered zircon and hafnon are observed at the surface of gels resulting from the complete alteration of Zr- or Hf-bearing borosilicate glasses at 90°C and pH 1. The unusually low temperature of formation may arise from the similarity of the local structure around Zr in the gel (from the altered glasses), the leaching solution and the zircon structure, in particular, the majority eight-coordination of Zr and the connectivity of Zr-sites with their surroundings. Similar behavior is expected for Hf, which mimics Zr speciation in solution and hafnon structure. This work expands the known formation methods of zircon and hafnon at low temperature, underlining the importance of amorphous precursors to facilitate crystal growth under unusual conditions.