Papers by Keyword: Bonding

Abstract: The design of the concrete mixtures of Ultra High Performances Fibre Reinforced Concrete (UHPFRC) is related to a densely compacted cementitious matrix and has outstanding material characteristics involving workability and high mechanical properties. Generally it is a combination between high strength concrete and fibres. UHPFRC offers high compressive strength which is higher than a normal concrete. The application of POFA as a cement replacement enhances the transport properties of concrete and contributes to a sustainable environment. The utilization of 50% UPOFA in mix design leads to develop a new class of concrete designated as GUSMRC. GUSMRC mixtures enhance the mechanical behaviour of concrete. GUSMRC with 50% replacement of the total binder content by ultrafine palm oil fuel ash (UPOFA) could contribute sustainability of environmental. The development of UHPFRC and its application in the field may contribute a good bonding strength at interface as a repair material between a new and old material. However, complex properties of materials can change dramatically when exposed to the elevated temperatures and adversely affected. The physical and chemical will change when occurred to heat. This paper investigates the change in mechanical properties of UHPFRC at elevated temperature and to determine the bonding strength between two layers which is overlay and concrete substrate

Abstract: The following work was focused on the analysis of adaptable pressurized sandwich components. The investigations were carried out to study the influence of internal pressure on mechanical characteristics. The bonding quality between core material and outer layers is of particular importance. For analyzing the bonding quality peel tests were conducted. In order to investigate the influence of the internal pressure and also of a bonding technique on bending properties four-point bending tests were carried out. In addition, the pressure characteristics were studied with compression tests during which a compression die was pressed into the component. After the compression tests, the rebound properties of pressurized and standard components were observed and compared.

Abstract: High density graphite disks and aluminum nitride ceramics powders have been utilized to obtain joints by Spark Plasma Sintering technique. The joining was carried out in vacuum, at temperatures of 1700°C, 1800°C and 1900°C, under the pressure of 50 MPa with a constant dwelling time of 5 minutes The AlN ceramics to be joined were also synthesized by ceramic technology standard route by using AlN powders and 2.5 % wt.Y₂O₃ powders as sintering additive, which were added in order to increase densification rate and by thus, thermal conductivity. The joining of AlN/C was performed both without and with the aid of a ceramic powder composite AlN+Y₂O₃+C film, as interlayer. Besides the crystalline phases (AlN and C), the Al₅Y₃O₁₂ compounds with a cubic crystallographic structure were identified by X-ray diffraction. The optical microscopy images revealed that all samples, both without and with film as interlayer, had strong joined areas, without any defects and discontinuities at interfaces. The Vickers microhardness and Young Modulus values measured by nanoindentation have shown that using of the film as intermediary layer was leading to the highest values of mechanical properties (HV = 8 – 23 GPa and E= 227-512 GPa) at the AlN/C joints interfaces.

Abstract: Mechanism of CNT-metal bonding is investigated using molecular dynamics in this study. Both bonding and debonding process are considered. It is shown that the bonding can be achieved at a temperature lower than the melting point. The surface melting and capillary wetting dominate the bonding process. In addition, there are two potential failure positions, one is at CNT-Ni interface and the other is at nickel surface which are determined by the strength competition of these two interfaces. To obtain high bonding strength we should form coalescence structure between CNT and the metal at a higher temperature to achieve larger contact length. Also we find that the debonding process experiences elastic deformation followed by debonding at CNT-Ni or Ni–Ni interface.

Abstract: The topology of electron density is a sketch that gives a clear picture about electronic distribution and details information of natural molecular bonding. In quantum mechanics or particularly in quantum chemistry, the electron density is a measure of the probability of an electron occupying at any infinitesimal element of space surrounding at any given point.Studies about the topology of electron density in Cd_0.5Zn_0.5S at plane (101) were conducted by the application of density functional theory (DFT) within linear augmented plane wave (LAPW) by using the WIEN2k software. In this calculation, generalized gradient approximation (GGA) methods were used to calculate the exchange-correlation potential of the electrons. Based on this calculation, the topology of electron density were presented in a contour plot (2D) and also inarelief map plot (3D) in order to see the way electron density, ρ of Cd_0.5Zn_0.5S defines the gradient field and hence the bonding type. From these plots, we identified the bond paths that coincide with the contours of electron to suggest that Cd_0.5Zn_0.5S exhibited characteristics of covalent and a slightly ionic bond character.

Abstract: Solid Bonding based welding processes allow to obtain defect free joints with low residual stress and low distortion. However, the engineering and optimization of solid bonding processes is difficult and requires a large number of time and cost consuming test trials. In this way, proper numerical models are essential tools permitting effective process design. The aim of this research was the comparison of the material process conditions during two different manufacturing processes taking advantage of the same metallurgical phenomenon, namely solid bonding. Linear Friction Welding, used to weld non-axisymmetric components and Accumulative Roll Bonding, used to increase the mechanical properties of sheet metals, were considered. Numerical models were set up, validated and used to design the process by studying the complex material behavior during the solid bonding of different aluminum alloys. An implicit approach was used for the Linear Friction Welding and Accumulative Roll Bonding processes, leading to the understanding of the main process variables influence on the field variables distribution and the occurrence of actual bonding.

Abstract: This study analyzed the bond line strength of Eucalyptus sp. specimens submitted to shear and perpendicular to grain tensile forces, depending on the wood quality machined surface. The woods plans were glued with two different polyvinyl acetate adhesives. The bonding surfaces were milling with three different feed speeds; 6.0, 11.0 and 15.0 m/min, corresponding to the feed per tooth of the cutting tool; 0.86, 1.57 and 2.14 mm, respectively. The specimen types corresponded to the standards according to ABNT NBR 7190/1997. The cutting plane considered only the geometry of milling due to the bond line joint strength. To explain the experimental results, was proposed a linear elastic model to machined wood and bond line. For the two adhesives used, the experimental results suggest that the greatest perpendicular to grain tensile strength and shear strength were obtained to bond surface machined with the intermediate feed speed namely 11 m/min, for others two feed speeds and in the shear strength case, was not observed a distinction between them, in the perpendicular to grain tensile strength, the feed speed 6.0 m/min presented a higher strength than the machined surface with 15.0 m/min. The model reproduces the behavior of the experimentally results obtained for the two tests, and so it can be readily applied as a tool for evaluate the machining feed speed and the bond line joint strength.

Abstract: The effect of substrate cleaning using ultrasonic cleaner on tungsten carbide was investigated. The surface energy of the substrate was measured using two liquids with dominant polar and dominant dispersion components which were distilled water (DI) and methylene iodide. Owens-Wendt method was carried out to calculate the surface energy of the substrate. The result showed that the cleaning process using solvent B (alkaline, DI, acid, DI, DI, alcohol) for 20 minutes without the wiping process led to the highest surface energy of 126.3399 dyne/cm with the polar component of 80.538 dyne/cm. Findings from this research suggested that type of solvent, cleaning time, and interactions among solvent type, cleaning time, and wiping process significantly influenced surface energy of the substrate.

Abstract: For achieving high-temperature resistance and a broadband of microwave transmission, ceramic metamaterials consisting of fused silica ceramic substrates and electrically conductive networks/ arrays are desirable. A new strategy of fabricating the fused silica metamaterials is to combine the low temperature co-fired ceramic (LTCC) technique with a method of ceramic joining via green tapes. The important part of the new strategy lies in the preparation of suitable green tapes that are co-firable with a conductive silver-based film/strip and have a strong affinity to the fused silica substrates. Therefore, in this paper, three green tape materials were prepared and intensively characterised using scanning electron microscopy, x-ray diffraction, dilatometry, dielectric measurement, etc. It was found that the tape materials were based on dielectric glasses and crystalline phases of major eulytite and minor cristobalite, leading to rather low levels of dielectric constant (<6) and loss tangent (in the order of 10^-3). The three tape materials also had different levels of thermal expansion coefficients, co-firability with a conductive silver-based paste, and bondability to the fused silica substrates. These findings suggest that one can achieve desirable ceramic matematerials with well-controlled shapes and dimensions of the condutive networks/arrays after properly laminating the green tapes between the fused silica substrates.

Abstract: In order to improve the water resistance of silicate wood adhesive, a kind of silicate adhesive was prepared from water glass with silica as curing agent, and ammonium stearate as modifier. The chemical structure, surface morphology and thermal properties of the silicate adhesive were characterized by Fourier transform infrared spectrometer, scanning electron microscope, and thermo-gravimetric analyzer. As the two main measures of adhesion properties, the bonding strength and water resistance were also determined. The results showed that ammonium stearate was successfully introduced into the molecule structure of silicate, the silicate adhesive have good thermal stability in the range of 30~800 °C and the modified silicate adhesive had more smooth cured morphology. The bonding strength and 24h water absorption rate of poplar plywood glued by the silicate adhesive was 0.71 MPa and 22.81%, respectively, reaching the grade II of plywood performance's national standard.