Applied Mechanics and Materials Vols. 217-219

Abstract: Improving the efficiency of equal-channel angular pressing (ECAP) necessitates predicting the location of fracture and the number of ECAP passes required when fracture is formed. However, the damage mechanism in ECAP-processed materials remains insufficiently understood. Surface fracture formation during the ECAP of 6061 Al-T4 alloy was investigated by finite element simulation and experimentation. The simulation of damage distribution in the sample was based on the Cockcroft and Latham criterion. Fracture formed in the upper and lower surfaces of the sample, a finding that is in good agreement with the simulation results for damage factor. A critical damage factor, calculated from the experimental data, accurately predicted the number of ECAP passes required when surface fracture is formed. Tensile stress was caused by various strain rates in different parts of the sample cross-section as the sample was pressed through the bend channel; this stress was the main driver of damage formation.

Abstract: Non-alloyed P355NH steel according to EN 10028-3:2003 belongs to a group of fine-grained steels for pressure vessels being used in welded construction at decompression chamber for divers. Values of the chemical, structural and mechanical characteristics and steel toughness experimentally determined fit the analyzed steel in P355NH steel group according to EN 10028-3:2003. The toughness of the analyzed steel at the test temperature of -30°C is characterized by high values of fracture energy KV in longitudinal direction between 48 and 86 J and on transverse direction between 17 and 34J. Steel toughness at the test temperature of -30°C required by ABS standard (in Section 4/5.3 and Table 1) provides for breaking energy KV of min. 35J, with ductile fracture surfaces, value that is not respected at some lots of the three batches (A, B, C) of steel. Finally, based on the direct correlation established between HV10 hardness of the fine structure and the toughness it was made a selection of the lots of non-alloy steel P355NH which correspond to ABS norm for welded construction of the decompression chamber for divers

Abstract: It is well-known that using pulse voltage could improve the machining accuracy in ECM process. However, the tool electrode wear occurs under some machining conditions in pulse ECM. In order to acquire the high machining accuracy, a method to eliminate the electrode wear by raising the low-level voltage was proposed and the relation between the low-level voltage and the machining accuracy was experimentally investigated in this research. It was found that the low-level voltage of 2V could not only prevent the tool electrode wear, but also improve the machining accuracy and the machining speed. In addition to the low-level voltage, the influence of the pulse duty ratio on the tool wear, the machining speed and accuracy was investigated. It was found that the raised low-level voltage was also effective when the duty ratio was increased and the increased duty ratio itself reduced the tool electrode wear.

Abstract: The electrical properties of AlGaN/GaN heterojunction high electron mobility transistor (HEMT) are simulated by using sentaurus software. This paper compares two structures, the HEMT with GaN cap layer and the HEMT without GaN cap layer. The sentaurus software simulates the DC and AC characteristics of the two AlGaN/GaN HEMT structures. The HEMT with GaN cap layer can increase the maximum transconductance g_m from 177ms/mm to 399ms/mm when the doping concentration of the cap layer is 3×10¹⁸cm^-3 compared with the other structure under the same conditions. The simulation results indicate that the HEMT with cap layer can increase maximum transconductance g_m, saturation current I_ds, current-gain cutoff frequency f_T, maximum oscillation frequency f_max and reduce the series resistance of the drain to source compared with the HEMT without GaN cap layer. The large I_ds of the HEMT with cap layer is attributed to the increase of the concentration of two dimensional electron gas (2DEG). Moreover, the change of the doping concentration of the cap layer will affect the g_m and I_ds.

Abstract: A simple catalytic kinetic spectrophotometric method was developed for the determination of trace Ru (III) in the range of 0.033–1.00 μg/L. The method is based on the catalytic effect of Ru (III) on the oxidation of rhodamine 6G (Rh 6G) by bromate in micellar media. The reaction was monitored spectrophotometrically by measuring the decrease in the absorbance of Rh 6G at 520 nm with a fixed-time method. The limit of detection is 0.010 μg/L Ru (III). The relative standard deviation for the determination of 0.010 and 0.020 μg/25mL Ru (III) was 2.9 % and 2.5 %, respectively. The method was applied to the determination of Ru (III) in some ores and metallurgy products.

Abstract: A rig was built to study the friction damping characteristics of metallic materials with non-conforming contact. The hysteresis curves which show the relationship between the tangential force and relative displacement of the contact between a spherical surface and a flat surface were measured. The effects of the vibration amplitude on the friction damping characteristics of the contact were investigated. The results show that both the amplitude of friction force and the friction coefficient increase as the vibration amplitude increases at first and then reach to a constant value. The equivalent stiffness decreases as the vibration amplitude increases, while the equivalent damping increases at first and then decreases slowly. And both of them trend to constants when the vibration amplitude is larger than 4.8μm.

Abstract: Based on the basic principles of heat transfer, the two-dimensional stable state cylindrical coordinate solid heat conduction differential equation having no inner heat source is established. Use the ANSYS software to establish the temperature field finite element analysis model of rotating and stationary rings and carry on the solution to the temperature field. The temperature distributing rules of rotating and stationary rings are obtained at the same time. According to thermo-elastic deformation theory, numerical analysis method and separation method are applied to resolve and analyze thermal-structural coupling deformation of rotating and stationary rings.

Abstract: The effects and the mechanisms of namo TiN on the high chromium cast iron are studied, the material has been prepared through infiltration casting and addition of high carbon ferrochrome powder and nano TiN powder. The alloy is formed on the surfaced of guide plate, and the wear resistance of alloy have been studied by means of SEM, XRD micro-analysis and wear-resistant performance. The grain size and the type of carbide in the organization are affected by nano TiN, and the wear resistance of carbon chromium alloy layer is affected by the type of carbide; when the addition of nano TiN is 1% (wt), the grain size is apparently refined, overeutectic primary M7C3 in the hypereutectic is precipitated uniformly in considerable amounts, therefore the wear resistance of alloy can be improved effectively.

Abstract: The most widely used method of liquefaction prediction are perform in deterministic process. The deterministic method according to seismic Chinese code is introduced by Z. CAO et al (2008). The deterministic method used the standard penetration test (SPT) to evaluate the liquefaction of soil. With this method, liquefaction of soil is predicted to occur if the factor of safety(FS), which in the ratio of critical SPT-N value(Resistance) over the actual measurement SPT-N(Load), is less than or equal to one. If the factor of safety greater than one, no soil liquefaction is predicted. Because the significant uncertainties in variable involved in the deterministic factor of safety, the probability method need to use. because the significant uncertainties in the random variables involved, the probabilistic method is needed to predict liquefaction. Probability of failure may be performed in which the liquefaction potential is assessed in term of probability safety factor (central safety factor). The study case is shown that the probabilistic method given the much more information for engineering decision than the deterministic method that given only the safety factor..

Abstract: According to the standard definition of radial circular error, set up any space surface radial runout errors of least squares mathematics model. The coordinate origin of the model can be freely selected, nor equal angle interval among discrete sampling points. Analysis by computer simulation, results show that the model developed is right and pratical. On the basis of mathematical models, using four direct algorithm for unconstrained optimization, radial runout errors can be evaluated in accordance with the minimum conditions. Mathematical models can be used for three-coordinate measuring machine and also available for other intelligent instrument for measuring parts of the radial runout errors.