Key Engineering Materials Vol. 861

Abstract: Moisture content is an important parameter of concrete material, and ultrasonic excitation infrared thermal image detection technology is a new nondestructive detection technology. In this paper, the relationship between concrete moisture content and ultrasonic excitation infrared thermal image detection technology is studied by experiment and numerical simulation. The moisture content of concrete was changed by immersion method, and the time of immersion was controlled to control the moisture content. It is found that with the increase of water content, the maximum temperature rise of the defect area decreases gradually, that is, the detection effect is weakened. The results of numerical simulation are in good agreement with the experimental results, and the simulation is effective to some extent.

Abstract: In this work, the enhancement of thermal and sound insulation properties of cement composite roofing tile with nanocellulose coated pineapple fiber and modified waste tire rubber is studied. The composite was composed of bacterial nanocellose (BNC) coated pineapple fibers, modified rubber particles, platicizer and type I Portland cement in the weight ratio of 10:50:0.8:100 with the water to cement ratio (w/c) of 0.5. The thermal conducitity of the fiber rubber cement composite could be reduced to 0.1080 ± 0.0048 W/m.K as opposed to 0.3810 ± 0.0041 and 0.5860 ± 0.0050 W/m.K for the fiber cement and the rubber cement composites, respectively. Moreover, the noise reduction coefficient of the fiber rubber cement composite could be increased to 0.2832 as opposed to 0.2143 and 0.1899 for the fiber cement and the rubber cement composites, respectively. These results revealed that adding nanocellulose coated pineapple fiber and modified rubber particles together to the cement composite can enhance the thermal insulation and sound absorption abilities of the composite roof tile significantly better than adding each constituent separately.

Abstract: This paper uses a fluorescence microscope to study the microstructure of dry modified asphalt, and compares and analyzes the micro and macro performance of dry and wet modified asphalt. The results show that: in terms of micro performance, when the modifier content is 6%, the dry modifier (SBS-T) becomes to a compact network structure in the asphalt when the shear time is 5 minutes, and it takes 45 min for the modifier to achieve the same result to the wet method. And the macro performance indicators of penetration, softening point, ductility, and viscosity show that the modification effect of asphalt is better by dry modifier is 5 minutes after shearing than the modification effect of asphalt by wet modifier is 45 minutes.

Abstract: This research showed the results of experiments effect use of oil palm fibre (OPF) from oil palm industry as partial replacement for ordinary Portland cement. Research on the reuse of waste materials in the concrete industry has been quite intensive in the past decade. The objective of this research is to identify the Effect of oil palm fibre as a partial cement replacement in the production of concrete. After the treatment, the economical ways to dispose of it is by using landfill method. But due to a limited landfill site in Malaysia and it is the temporary solution for the disposal of the waste, it becomes a problem to Malaysia and the number of the oil palm fibre keeping increase year by year because of the population increase year by year too. The results showed that oil palm fibre (OPF) greatly improved the compressive and flexural strength of concrete. The rate of water absorption of oil palm fibre (OPF) concrete was reduced as oil palm fibre filled up the existing voids, making it more impermeable. However, the compressive strength of the oil palm fibre concrete decreases gradually when the amount of oil palm fibre (OPF) increased. It can be concluded that the optimum percentage of oil palm fibre as a partial cement replacement is 10%. In this direction, an experimental investigation of ultrasonic pulse velocity, carbonation test, compressive strength, flexural strength and water absorption was undertaken to use oil palm fiber and admixtures as partial replacement for cement in concrete.

Abstract: The different initial morphologies of polished surface is one of the important factors affecting the quality of laser polishing. In order to investigate the flow characteristics of the molten pool with different morphologies, a two-dimensional (2D) axisymmetric numerical model is established based on the COMSOL software. The nonisothermal flow interface is used to couple the heat transfer and fluid flow, and simulate the evolution process of the molten pool with three different surface morphologies. The results show that the initial shape is a smooth plane, the flow velocity of the molten pool is stable and always in thermocapillary regime, then the protrusions were generated at the edge of the molten pool. Likewise, with the increase of the surface curvature, the capillary becomes the main driving force to eliminate the surface asperities. While the flow velocity and instability of the molten pool enhance, and the depth of the molten pool increases with the heat transfer generated by the mass flow along the z-axis direction.

Abstract: COMSOL Multiphysics software-based three-dimensional finite element analysis is widely used in the performance simulation of thermoelectric devices. In this study, this software is used to simulate the heat transfer processes and power generation performance of micro-thermoelectric generators based on a microporous glass template. The temperature and electrical potential fields are coupled to each other through the thermoelectric effects during the calculations. The power generation performances of micro-thermoelectric generators with different template heights (d) for various temperature differences between their hot and cold ends (∆T_h-c) are calculated. For the micro-thermoelectric generator that included four pairs of TE couples, the temperature difference between the two sides of the TE columns (∆T_TE) and the open circuit voltage (U_oc) both increased with increasing d, but the growth rate gradually decreased. When d is greater than 0.2 mm, the increment basically becomes negligible. The maximum output power (P_max) first increases and then decreases with increasing d, reaching a maximum value when d is 0.2 mm. Therefore, we can optimize the size of device according to the simulation results to ensure that the device produces the optimal output performance during the experiments. A model with the same parameters used in the experiment (i.e., d=0.2 mm) was then established and it generated a U_oc of 35.2 mV and a P_max of 228.8 μW when ∆T_h-c was 107.5 K (∆T_TE = 97.55 K). The errors between the simulation and the experimental results are small and thus also verify the accuracy of the power generation performance test results.

Abstract: Numerical model of the convective-radiative heat transfer of porous media was proposed. A stainless wire-net was used as porous media. The physical properties, consisting of porosity (φ) and optical thickness (τ₀), of porous media were independent variables. The air velocity was reported in the form of Reynolds number (Re). Two equations of the conservative energy with local thermal non-equilibrium were analyzed. The gas (θ_f) and solid (θ_s) phases of conservative energy equation inside porous media were investigated. The radiative heat flux (ψ) at down-stream of solid phase emitted into outside was dealt by the P₁ approximation. From the study, it was found that the level of θ_f and θ_s decreased as Re increased because the effect of convection heat transfer. Inversely, the level of ψ increased as increasing Re. The level of θ_f, θ_s and ψ were decreased as φ increased owing to a lower volume of material depended on the increasing level of φ resulting to the heat transfer rate became lower. The level of θ_f, θ_s and ψ gave increased with τ₀ becaues a wider distance in absorping energy leading to a higher emission energy from the porous media was achieved.

Abstract: The cone tube is an important part of the circuit connector, which has high requirements for its forming quality. In this paper, the cone tube is taken as the object, the finite element model is established, the radial forging process of the cone tube is simulated, the influence of process parameters such as axial feed and friction on the thickness of the cone tube is studied, and the influence law is analyzed, which has certain reference value for the analysis of the forming law of the radial forging.

Abstract: The aim of the study is to construct a mathematical model to describe the effect of a magnetic field on the melt crystallization, in particular cast iron. The authors’ research is based on the hypothesis of the certain energy function existence in the short-range order region, which describes the equilibrium state of the "fluid - short-range order" thermodynamic system. Using the hypothesis, we simulated the effect of a magnetic field on the melt crystallization process, which is based on the fundamental laws of statistical physics and thermodynamics and includes four components: a model of the stationary state of the short-range order region, a model for determining the energy function of the short-range order region, a model of the effect of a proportional magnetic field, a model the effects of a commensurate magnetic field on the crystallization of molten iron. Being based on the simulation results, test calculations were performed, the results of which are confirmed by previously known studies. The simulation results showed that the influence of a magnetic field on the crystallization of melts is insignificant in comparison with thermal motion. The authors of the work believe that the magnetic field acts on the region of short-range order at the formation time at a fluctuation temperature that is much lower than the equilibrium one.

Abstract: The various mode of stresses for the interaction between two inclined cracks in the upper part of bonded two half planes which are normal stress (Mode I), shear stress (Mode II), tearing stress (Mode III) and mixed stress was studied. For this problem, the modified complex potentials (MCPs) method was used to develop the new system of hypersingular integral equations (HSIEs) by applying the conditions for continuity of resultant force and displacement functions with the unknown variable of crack opening displacement (COD) function and the right hand terms are the tractions along the crack. The curve length coordinate method and Gauss quadrature rules were used to solve numerically the obtained HSIEs to compute the stress intensity factors (SIFs) in order to determine the strength of the materials containing cracks. Numerical solutions presented the characteristic of nondimensional SIFs at the cracks tips. It is obtained that the various stresses and the elastic constants ratio are influences to the value of nondimensional SIFs at the crack tips.