Papers by Keyword: Thermal Effect

Abstract: NdFeB magnets were first developed in 1984 and are the most powerful permanent magnets that may possess energy products up to 60 MGOe. However, their working temperature and corrosion resistance are lower as compared to that of Alnico and SmCo magnets. Demand of NdFeB magnets recently has increased due to rapid growth of electrical vehicles. In this research work, NdFeB magnets developed through powder metallurgical technique are investigated for thermal effect on magnetic characteristics. The effect of increase in temperature on remanence, coercivity and energy product were measured using pulsed field magnetizer. Samples for testing were prepared from sintered bricks using wire cut machine. Demagnetization curves for the samples were measured at temperatures in the range of 20-110°C, and the results were analyzed. Decline in magnetic characteristics with temperatures is noted. Performance of the magnets with increase in temperature is essential to be analyzed specially for their use in high-speed motors.

Abstract: Since the material properties of paperboard depend on the processing strain rate and the temperature elevation of the paperboard, the mechanical conditions of the scoring tool (creasing knife) are important for precisely and stably folding the scored zone of the paperboard. When the temperature and the indentation velocity of the creasing knife are changed irregularly during the scoring process, the permanent-indented (residually scored) depth of the paperboard seems to be affected by the temperature and the indentation time of the creasing knife. Although the temperature-dependent and time-dependent behavior of several thin paperboards have been known in the past, their combined behavior was not sufficiently discussed regarding the crease bending characteristics of the paperboard. In this work, the time-dependent and temperature-dependent scoring, and the corresponded bending characteristics of liquid-container-purpose paperboard of basis weight 313g/m² (thickness of t = 0.47mm) were experimentally investigated using a bending (folding) tester, when varying the holding time and the temperature of a flat-edge creasing knife at two levels of the normalized indentation depth d/t = 0.68 and 1.02. As the results, the first peak bending moment M_p1, the first stiffness C₁ (the gradient of bending moment resistance by the folding angle at an angle of 0—4 degrees), and the rating bending moment resistance at the right-angle M_90,1(0) were characterized with the holding time and the temperature elevation of the creasing knife at the pre-stage (scoring) process. Also, some explicit expressions of C₁, M_p1, M_90,1(0) with the permanent scored depth were revealed as a static relationship. It is concluded that the temperature variation and the holding time of the creasing knife are important parameters which must be controlled in the manufacturing process of liquid package.

Abstract: A thermodynamic model for cellular glass pore-formation has been developed on the basis of natural volcanic silicate and aluminosilicate glasses. The energy expenses for heating the materials, chemical reactions, breaking the structural bonds of water hydrates, evaporation of the released water, and pore formation of the glass mass are determined sequentially. The enthalpy and Gibbs energy of the complex gas-forming agent HNO₃ + SiC are calculated.

Abstract: This study is designed to investigate the influence of multi-beam matrix laser cutting process on NAND Flash package quality, and find out the important process parameters of multi-beam matrix laser process are defocus amount, laser power, cutting speed and material thickness. Then use the finite element analysis software ANSYS to obtain the minimum temperature influence, stress and strain, and use Taquchi method and variance analysis (ANOVA) to find the optimal temperature combination, the optimal combination of stress and strain and its contribution degree. Finally, the reliability is tested by verification experiments, and the error is found to be within 3.638%. It is confirmed that the optimized parameter combination has high repetitiveness. It is hoped that this study can contribute to the multi-beam matrix laser cutting process.

Abstract: Lump solid fuel is one of the most important charge material components in layered cupola units. It determines layer gas permeability, conditions development for heat exchange with gasses in it, heat generation process rate and intensity. In present-day conditions of material shaft melting charge materials of boosted fractional makeup are used, as well as oxygen, carbon and hydrogen enriched air. In the circumstances the issue of ensuring the best gas dynamic conditions become particularly vital, both for the furnace low and high temperature zones, at the charge component oxidation and recovery processes development. Under conditions of continuous charge component movement in the layered unit workspace they are subjected to abrasive action of charge components with the result, which may be described by mechanical properties based on mass yield of certain fractions after disruption in a closed drum М10 and М40. Coke lump behavior at relatively high temperature (below 1100°С) in the presence of complete fuel combustion products СО₂ and Н₂О may be implicitly evaluated by coke strength after reaction (CSR) and coke reactivity index (CRI). When studying, particular combustion features of coal coke in conditions close to shaft cupola unit operation data of the total differential scanning calorimetry (DSC) curve were used. Temperature ranges of intensive heat generation were determined from the beginning of active coke sample oxidation to completion of the burnout period, as well as apparent heating capacity and coke combustion thermal effect.

Abstract: The properties of “water glass – graphite microparticles” composite material (CM) have been researched and qualitative and quantitative phase analysis of the CM structure has been done. Experimental samples of the CM with filler particles (graphite) and a few micrometers in size have been studied with X–ray diffraction and electron microscopy. Fire–resistance test of the composition has been conducted. Fire–resistance limit for the test samples of composite material is determined by the loss of its insulating ability (I). Fire–resistance limit I15 equal to 15 minutes has been obtained in accordance with the requirements of regulatory documents. It is shown that the research material is characterized by thermal stability and maintains its composition and structure under high temperature exposure. Composite material with the obtained characteristics can be used as protective coatings for building structures to increase fire resistance and reduce fire hazard.

Abstract: The problem of reliability prediction and assurance is characteristic of wireless devices based on nanoscale multilayer heterostructures because of the sensitivity of heterostructures’ parameters to the degradation processes due to the thinness of layers. In the current work, the degradation of the nanoscale AlAs/GaAs resonant-tunneling heterostructures due to the diffusion of the constituent elements was investigated. Analysis and comparison of data on Al and Si diffusion coefficients in GaAs shows that they strongly vary depending on the conditions of heterostructure fabrication. This happens while the defect density of the grown heterostructures depends on a large number of technological factors such as the substrate temperature during molecular beam epitaxy, chamber pressure, annealing temperature and time, defect density in the initial substrate, and many others. The values of the diffusion coefficients obtained by the authors of this article by IR spectral ellipsometry are consistent with the data of foreign researchers. This allows their use to predict the reliability of resonant tunneling diodes and nonlinear radio transmitters based on them.

Abstract: TRISO coated fuel particle is the most important component in HTR fuel, the silicon carbide (SiC) coating layer is regarded as the pressure vessel to contain the fission products. During reactor operation, the inner pressure resulting from fission products and pyrocarbon (PyC) thermal effect will contribute to the failure of TRISO-coated particles. The higher temperature will result in the increasing of inner pressure and PyC thermal expansion, which will then change the stress of SiC layer. Considering the effects of temperature on inner-pressure expansion and elastic strain into the pressure vessel failure model, thermal effects on the stress of TRISO-coated particles were studied with analytical solution. The results indicated that the effects of inner pressure on the particle stresses were increasingly highlighted at the late stage of irradiation. And the increasing temperature caused a slight effect on PyC elastic modulus while elastic strain is unaffected greatly, either. Therefore, CFP stresses remain unchanged basically.

Abstract: To understand the thermal effects on material removal at atomic level, molecular dynamics (MD) simulation and optimization method are performed with the aid of Morse, EAM and Tersoff potential. The heat distribution is showed in 3D images under various parameters. The simulation results reveal that the heat distribution is roughly concentric around the tool edge and a steep temperature gradient is observed between diamond tool and chip. During material removal process, there is a narrow region with high temperature in shear zone where most of heat generated due to plastic deformation of workpiece material, the high temperature extends from here to chip, diamond tool and workpiece, but the highest temperature lies in chip. Compared with low speed, a higher temperature region below the tool edge implied a larger shear stress is built up in a local region and a rougher machined surface is generated at high cutting speed.

Abstract: In the present paper, the characteristic and the application of ultrasonic fatigue testing technology is illuminated. The main problems i.e. the size effect, the thermal effect and frequency effect due to the high frequency are discussed. The results show that: 1. As there is a size effect, a uniform specimen size should be adopted in the very-high cycle fatigue standard and for special designed specimen the designed size should be noted along with the fatigue test results; 2.the heat generation attributes mainly to the low yield strength and the high applied stress, as a result, ultrasonic fatigue testing technology can be mainly applied to the ultra-high cycle fatigue test of high-strength steel; 3.the frequency effect is related to the crystal structure of metallic materials, however, ultrasonic fatigue testing technology can be applied to conduct the comparison of the fatigue properties of the same steel grade before and after the smelting process.