Applied Mechanics and Materials Vols. 52-54

Abstract: Detecting the existence of a crank in the Stephenson-Ш six-bar linkage is one of the most difficult problems encountered in the mechanism synthesis. Based on the model established for the circuit analysis of the Stephenson six-bar chains, through judging whether there is a dead-center position in the circuits of this linkage, this paper presents a new method for identifying the existence of a crank in the Stephenson-Ш six-bar linkage. Some examples are given to demonstrate the validity of this method.

Abstract: A new method for identifying the dead-center positions of the Stephenson six-bar linkage is presented by this article. This method uses the input-output polynomial equation of the linkage and the corresponding Sylvester's resultant to formulate the necessary condition of the dead-center configurations as a polynomial equation in terms of the input parameter; then through a simple analytical method to obtain all the truly dead-center positions among the double roots to the condition equation. An example is given to demonstrate the validity of this method.

Abstract: The derivative free trust region algorithm was considered for solving the unconstrained optimization problems. This paper introduces a novel methodology that modified the center of the trust region in order to improve the search region. The main idea is parameterizing the center of the trust region based on the ideas of multi-directional search and simplex search algorithms. The scope of the new region was so expanded by introducing a parameter as to we can find a better descent directions. Experimental results reveal that the new method is more effective than the classic trust region method on the testing problems.

Abstract: Wedge trust region method based on traditional trust region is designed for derivative free optimization problems. This method adds a constraint to the trust region problem, which is called “wedge method”. The problem is that the updating strategy of wedge trust region radius is somewhat simple. In this paper, we develop and combine a new radius updating rule with this method. For most test problems, the number of function evaluations is reduced significantly. The experiments demonstrate the effectiveness of the improvement through our algorithm.

Abstract: Special numbers overflow and underflow threaten the software security in programs or software. To find the overflow vulnerabilities features, we design a multi-dimensional structure according to IEEE 754 floating point special numbers formats. Based on special numbers definition in language and arithmetic operation overflow ranges, we analyze the overflow and underflow properties of special numbers arithmetic operation in algebra systems. We test the arithmetic overflow and underflow of floating point special numbers in different CPUs. The experimental results indicate the floating point overflow exists in many kinds of language programs and binary executable software.

Abstract: The shearing machine is an important and complex accessory equipment of the continue-mode rolling mills. Its mechanism design scheme determines the shearing quality of steel. The shearing machine mechanism design (SMMD) contains multi conflicting technical requirements and belongs to a multi objective optimization problem with the nonlinear constraints. Recently, ant colony optimization (ACO), a swarm based computing methods, has demonstrated its superiority in many complex optimization problems. This paper presented a quasi TSP-based SMMD model and an ACO algorithm for the SMMDP. The presented method dispersed the searching space of the design variables by setting several different search steps, and an ACO algorithm was adopted to search the best searching step of each design variable dynamically during the whole optimization process. Computational results showed that the proposed method can improve the computational accuracy and produce better solutions within short running times.

Abstract: The effects of steel case confinement for the aluminized explosive on underwater explosion(UNDEX) were experimentally and numerically investigated. The experimental results using 1kg cylindrical charge cased 6mm steel shell, show that steel case enhance the peak pressure, impulse, shock wave energy and decay time relative to the bare charge. The effect of different thickness of steel case was analyzed. With the increase of the case thickness, the shock wave were enhanced first and weaken later, and there is a lag-effect for the peak pressure of shock wave. There is an optimal case thickness which could maximum enhance the peak pressure. According to dimensional analysis, it's found that the ratio of case mass and charge mass( ) is a better dimensionless parameter to estimate UNDEX for a cased charge.

Abstract: In Quercus aliena var. Acuteserrata community, phanerophytes (Ph) accounting for 58.7% was main Life form. Hemicryptophytes (H) with 28.1% was the second in Qinling Mountains. Mesophyll which accounted for 61.64% was major leaf physiognomy, and microphyll the second accounting for 27.40%. Simple leaf taking 84.93% was primary leaf-form. Herbaceous leaf accounted for 80.82% and was a major type of leaf property. The temperate elements, which were 43.17% of the genera, were in dominant position and were consisted of 98 genera; the tropical areal types including 58 genera accounted for 25.55%. These showed that Quercus aliena var. Acuteserrata community has the transitional character, that is, it is in the ecotone.

Abstract: In this article, we have carried out the Ni based self fluxing alloy powder and studied the effect on the laser alloying of 45steel layer which contains different weight percentage of nano-SiC powders. Experimental results show that the alloy layer which obtained by the optimized laser alloying process parameters (I = 38A, V = 100 mm / min, Δf=10mm, Ar gas protection) is smoothness, fineness, hardness and have a good metallurgical bonding. The test of tribological wear experiments shows that the wear capability of Ni-based powder made of laser alloyed layer is more excellent than that of the hardened 40Cr steel. And the tribological wear capability of the Ni-based alloy with SiC made of laser alloyed layer has been further improved. In the same process conditions, the addition of 20% nano-SiC is the best.Salt spray test shows that both the Ni and Ni/SiC composite coatings' corrosion is much stronger than that of the 45steel substrate. But with the added amount of nano-SiC increased the resistance of alloying layer corrosion decreased slightly. Finally, this paper use Grey comprehensive evaluation model to value the quality of the alloy layer. The evaluation vector shows that the laser alloyed layer which added 20% SiC has optimal overall performance.

Abstract: Electroslag Remelting (ESR) technology is a main method of special metallurgy; and split pillar is one of the most important mechanical units of ESR. The split pillar works not only as the mother body of ESR cross arm, but also as the rotation driving device of the cross arm. Since the tremendous mass of the cross arm and electrodes, serious inertia torque generates when the split pillar rotates, which leads to motion instability and problems of angle location and even safety threatens. In this paper, based on virtual machine technology, dynamic research of the rotation process of the electroslag-remelting-furnace split pillar was proceeded; influences of driving torque applied on the split pillar was researched, as the driving torque being constant, anti-step and with brake torque. 3D solid model of the split pillar and clamping device were established; main technical parameters were accomplished; and simulation research of the dynamic process was proceeded. It was found that, appropriate brake torque was important to better motion stability of the split pillar. The best brake torque was acquired, and the action time of the brake torque was obtained.