Applied Mechanics and Materials Vols. 313-314

Abstract: Double-stator switched reluctance machines benefit from a high torque density and a low radial force level in comparison with conventional switched reluctance machines resulting in a lower vibration and acoustic noise. Therefore, they are suitable candidate for automotive applications. However, torque pulsation which is also a source for vibration is still remained and should be alleviate by dimension optimization of the machine. This paper presents a design optimization of a double-stator switched reluctance machine for improving the magnetic torque quality of the machine. For this purpose finite element method along with response surface methodology is used to optimize three parameters of the machine to maximize torque quality factor i.e. the average torque to torque ripple ratio in the machine. Genetic algorithm method is also employed as an optimization tool. The aim of optimization is to maximize the ratio of average torque to torque ripple. Finite element results are presented to verify the optimization method.

Abstract: A new bridgeless powerfactor correction (PFC) converter is proposed in this paper. The proposed converter isbased on single-ended primary inductor converter (SEPIC). In the proposed converter, conductionlosses are reduced and efficiency is improved by eliminating bridge diodes. In addition, input currentripple is significantly reduced by utilizing coupled inductors. Like a conventional SEPIC PFCconverter, the proposed converter provides almost unity power factor (PF). Steady-state analysis ofthe proposed converter is performed. Experimental results based on a prototype are alsoprovided to verify the effectiveness and feasibility of the proposed converter.

Abstract: The vector control has become the first alternative in control of three phase induction motor. One of the vector control method which is commonly used is the direct torque control (DTC) method. However, this system has drawback due to the existence of torque ripples. The addition of the duty ratio control base on fuzzy logic can give better performance compared to conventional DTC. By doing an examination on DTC and duty ratio using small, medium and big capacities of three phase induction motors can be shown the influence from moment of inertia to rotor rotation. This paper uses MATLAB SIMULINK for the simulation study with three types of motor power, for example 1, 10 and 50 hp. It is shown that using the same parameters, a motor with a larger moment inertia gives a better performance in comparison to a motor with smaller moment of inertia.

Abstract: This paper designs a new and power-saving electrical power closed loading comprehensive test bench whose characteristic is AC generation. According to the requirement of non-uniform load, the paper applies the advanced virtual instrument technology to monitor and manage the test bench automatically. The results indicate that the test bench has the advantages of simple operation, complete function, high-level automation, easily implementing upgrading and expanding, low cost and remarkable energy saving result.

Abstract: The influence of solution heat treatment (SHT) temperature and time on the microstructure and mechanical properties of semi-solid 6061 aluminum alloy has been investigated in this study. Microstructure of the as-cast 6061 aluminum alloy mainly consisted of globular α-Al matrix and eutectic phase (α-Al + Mg₂Si) at the grain boundary (GB). Iron rich intermetallic phase was also observed at the grain boundary. Eutectic phase started to dissolve after solution heat treatment. The dissolution of eutectic phase increased with increasing solution treatment time, however, the amount of remaining eutectic phase was found to be slightly changed after solution treating longer than 1 h at 550 °C and 2 h at 530 °C. Hardness and tensile results of specimens after artificial aging were utilized to compare and select the optimum solution heat treatment condition cooperating with the microstructural observation. The optimum solution heat treatment condition of the alloy in this study was at 530 °C for 2 h.

Abstract: Coefficient of dynamic viscosity (η) for uniaxial rectangular bar of steel is calculated using creep simulation in Ansys. Norton Secondary creep law with coefficients at 600 ᵒC is used. Steel bar is then inflicted with some damage elements in order to investigate the evolution of dynamic viscosity for varying degree of fatigued specimen at constant rate and temperature. Isotropic damage parameter (D) based on the volume fraction of damaged elements is used to formulate a linear relation between the coefficient of viscosity and D. It is found that with 0.001 increase is damage parameter (D), almost 0.6% decrease on the value of Coefficient of dynamic viscosity (η) is observed.

Abstract: In this study, medium carbon low alloy steel was used to obtain bainitic structures. The lower bainite and tempered martensite-lower bainite structures were achieved by isothermal austempering and up quenching treatment, respectively. Based on the results obtained these structures showed a very good combination of strength and toughness. Furthermore, it has been shown that austenitization time and temperature, as well as austempering time and temperature play a major role in achieving ultra-high strength bainitic steels.

Abstract: Diamond-like carbon (DLC) films were deposited on magnetic recording head by Filtered Cathodic Arc (FCA) technique and a-Si base material was ion beam deposited as seed layer. To investigate the thermal stability of stack film, repeated cycle thermal heating at 200 °C was employed. Raman spectroscopy and nanoindenter (Hysitron) were performed to understand film structure and mechanical property as a function of thermal heating conditions. The roles of heating in material composition and wear behavior of DLC films are discussed. The Raman spectra revealed that G position, FWHM of G peak and Id/Ig change as with increasing heating cycle which agreed well with wear depth measured. With these results suggesting DLC film degraded with repeated heating at 200 °C.

Abstract: A bulk vacuum ultraviolet double frequency crystal KBe₂BO₃F₂ (KBBF) crystal has been grown successfully by using a method of oriented reduced-pressure melts growth, and the optical properties of the grown crystal, such as optical transparency and the second harmonic efficiency, were also measured. The results show that the high-frequency absorption edge is observed at 150nm and the optical transparency was up to 75% in the spectral range between 250nm and 400nm. The second harmonic efficiency was measured with an outer cavity frequency-doubling method and its maximal value was about 68.5%. The experimental researches indicate that the oriented reduced-pressure melts growth is a promising growth method for bulk KBBF crystal and it is possible for applying as a frequency-doubling device for the vacuum ultraviolet region.

Abstract: In this paper, an experimental study has been carried out to investigate the failure load and the failure mode of multi-pin joints of glass fibre reinforced composite laminates which have the stacking sequence of [0/±45/90/0]S subjected to a traction force. The laminates were manufactured by vacuum assisted resin infusion (VARI) and tested with a special fixture. The number of pins was set from 3 to 5, while there were two different arrang styles for each condition. The test results showed that the failure loads were directly affected by the number of pins and arrang styles.The ultimate failure loads increased with the number of pins.