Applied Mechanics and Materials Vols. 66-68

Abstract: In order to point out the relationship between the lower muscles force and 500m result f6r short track speed skating, the knee and ankle muscle strength of elite male skating athletes is measured and analyzed by IsoMed 2000 isokinetic testing system. Based on the features of athletes’ muscle strength, the study tends to find out the differences and drawbacks in short track speed skating athletes and to make further discussion on the laws and determinations of the event. The main conclusions are as follows: 500m result of elite male short track skating athletes are determined by that the muscle performances of fast speed, which including force opportunity, power ability and max-strength ability; the knee muscles are more important than that of the ankle’s; the strength with technique is the core factor for result.

Abstract: To improve equalization performance of the constant modulus algorithm (CMA), we study that error functions have an influence on the performance of the algorithm in this paper. Aiming at the character of different error functions, a new style of error function weighted by a variable coefficient is proposed. And a new CMA based on the new error function (VCMA) is proposed too. Because of variable-coefficient adjustability, the value of this new error function can become larger at the beginning of iteration and smaller at the end of iteration in the new algorithm. From gradient descent method, VCMA can have faster convergence rate and lower residual error than the CMA. Both theoretical analysis and experimental results have shown the effectiveness of the proposed algorithm.

Abstract: Anodized films on AZ91D magnesium alloy were prepared in sodium hydroxide based solution. Structure and properties of the anodized films were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical potentiodynamic polarization analysis. The results of XRD showed that the films were mainly composed of Mg(OH)₂ and Al(OH)₃. As the solution temperature increasing, the anodized films became thicker and denser, which could cover up the substrate. The films also became thicker and denser with the increase of anodizing time. The grain in the films grew fast when anodic current density increasing and a larger grain size would be found at a higher anodic current density. The results of microscopic analysis exhibited the porous-type anodic oxide, which was similar to the films on aluminum alloy. The results of electrochemical potentiodynamic polarization analysis showed that thermodynamic stability of the alloy had a certain improvement after anodization. The anodized films also exhibited an obvious increase of polarization resistance R_P and an obvious decrease of corrosion current density i_c. Discoloration time of drop test on the films lasted for 30 min, which indicated that corrosion resistance of the magnesium alloy was greatly improved by anodization.

Abstract: The fatigue crack growth experiments of 2024-T4 aluminum alloy were carried out to study the thickness effects on the fatigue crack growth rate. Round compact specimens with two different thickness, 3.8mm and 12.5mm, were subjected to Mode I loading with four R-ratios (0.05, 0.1, 0.5 and 0.75) and loading amplitudes. An optical reading microscope with a magnification of 40 was used to measure the crack length. Stable crack growth is characterized by the standard form of the Paris law, material constants of the Paris law corresponding to each R-ratio were obtained by fitting the experimental data. The fatigue crack growth rate of specimens with a thickness of 12.5mm is apparently higher than that of specimens with a thickness of 3.8mm when R-ratio is equal to 0.1, 0.5 and 0.75. While the effect of thickness is relatively less significant for the case of . It can be concluded that the fatigue crack growth rate increases with R-ratio or thickness when one of them is identical.

Abstract: In this paper, the effects of addition of solid lubricants on mechanical properties, tribological properties and cutting performance of ceramic cutting tool materials were analyzed. The problem that existing homogeneous self-lubricating ceramic cutting tool materials were not available to possess rational combination of antifriction and antiwear properties was pointed out. The main methods to acquire graded self-lubricating materials were discussed. The design concept and research prospect of graded self-lubricating ceramic cutting tool materials were proposed, which would have promising applications in the field of high speed cutting.

Abstract: Thixoforming is an effective near-net-shape forming process to produce components with complex geometry and in fewer forming steps. In this study, thixoforming was used to replace the conventional hot forging to form the auto claw-pole. The finite element code Forge2008^Ó was used to simulate the auto claw-pole thixoforming process. The results show that initial billet temperature, punch speed, die temperature and friction have strong impact on the forming process. Finally, the reasonable process parameters for the auto claw-pole thixoforming were obtained: initial billet temperature 1430~1440°C, punch speed 100~200mm/s and die temperature 300~400°C.

Abstract: 3003 Al alloy with different metallurgical quality were obtained by different melt-treatment methods, which were deformed by isothermal compression in the range of deformation temperature 300-500°C at strain rate 0.0l-10.0 s^-1 with Gleeble-1500 thermal simulator. The results show that the material is sensitive to positive strain rate. The hot deformation activation energy (Q) bears linear relationship with inclusion content (H) of 3003 Al alloy prepared by different melt-treatment, Q=35.62 H+171.58, the activation energy of 3003 Al alloy prepared by high melt-treatment is the lowest (174.62 KJ×mol^-1), which is beneficial to the material hot plastic deformation. The critical strain of 3003 Al alloy prepared by different melt-treatment methods is investigated through the work hardening rate. Finally, the critical conditions of the investigated alloy were determined to predict the dynamic recrystallization occurrence in the paper.

Abstract: Initial geostress is one of the most important factors in coal mining. By combination the finite difference software FLAC^3D with multivariate linear regression theory, 3-D initial geostress in situ is back analyzed, which also considers the effect of gravimetrical and tectonic stress. The back analysis results of initial geostress in Laohutai coal mine are in a good agreement with the in-situ test results, which provides theoretical support on prediction of geostress and also more convenient geostress data in coal mining.

Abstract: The distinguished characteristic of casting process of natural yellow clay-bonded green sand is a strippable sintering layer formed at the interface of casting and mould. Hot shake-out can be realized because this sintering layer can firmly attach to the casting surfaces to protect castings at elevated temperature. Better surface quality of castings is achieved after the sintering layer easily shed from the casting surface at room temperature. In this study, a series of tests were carried out to reveal the characteristic of this sintering layer. First, thermal gravimetric/differential thermal analysis (TG/DTA) method was used for detailed analysis the thermal property of natural yellow clay-bonded green sand. And, X-ray diffraction (XRD) analysis was employed to define the phase composition at variable temperatures. Then, sintering experiments were carried out on mixtures of natural yellow clay-bonded sand with iron powder or iron oxides under different conditions. Finally, the mechanical performances of sinter layer of natural yellow clay-bonded sand at elevated and room temperatures were investigated. The result revealed that natural yellow clay-bonded green sand is a kind of low grade molding sand, and iron oxides participate in the forming of sintering layer. The sintering layer of natural yellow clay-bonded sand were proved both excellent plastic at elevated temperature and brittle at room temperature, which coincides with its behavior in the casting process.

Abstract: As a new type of material, Glass Fiber Polymer-Soil nailing (GFP-SN) can replace the steel to be applied in the slope support, excavation support and other civil engineering. It was being concerned by more and more engineers. GFP-SN anchorage mechanism need be analysized and studied deeply to be used well. In this paper, numerical simulation software FLAC^3D was used to simulate the pullout tests of GFP-SN. The results show that the diameter of GFP-SN, the embedded length of GFP-SN and the maximum pull force had great influence on the drawing force, the pull force is proportional with them. Besides, it is obvious that the embedded mode of GFP-SN has a certain influence on bar’s drawing force property.