Advanced Materials Research Vols. 295-297

Abstract: This paper proposed a new configuration of magnetic bearings used in magnetic levitation stages. The equivalent current sheet model is introduced to calculate the levitation force of the proposed magnetic bearing, and the experiment result validates the correctness of the calculation method. The relationships of structural parameters to the levitation force and axial stiffness are studied, which prove that the new magnetic bearing has larger levitation force with lower axial stiffness over the working stroke and could be applied in ultra-precision magnetic levitation stages.

Abstract: In order to control the thermal stress of forming process, based on “element birth and death” technology of finite element method, a numerical simulation of three-dimensional temperature field and stress field during multi-track & multi-layer laser metal deposition shaping(LMDS) process is developed with ANSYS parametric design language (APDL). The dynamic variances of temperature field and stress field of forming process are calculated with the energy compensation of interaction between molten pool-powder and laser-powder. The temperature field, temperature gradient, thermal stress field and distribution of residual stress are obtained. The results indicate that although the nodes on different layers are activated at different time, their temperature variations are similar. The temperature gradients of samples are larger near the molten pool area and mainly along z-direction. Finally, it’s verified that the analysis results are consistent with actual situation by the experiments with same process parameters.

Abstract: In this paper, the dynamic performance of the single rod magnetorheological damper (MRD) without accumulator in different working status is researched, which is a new type of MRD developed by us to apply in the environment of explosion and shock. It is concluded that there is no offset force in the new MRD. The maximum damping force and energy absorption capability increase non-linearly with the excitation current and piston’s velocity. The mechanical model of this type MRD is proposed. By comparison of the results of tests with simulation, it is proved that the mechanical model proposed in this paper can simulate the dynamic performance of the new MRD accurately.

Abstract: Electromechanical coupling dynamic of parallel manipulator is a multi-input, multi-output, non linearity, tight coupling, and complex electromechanical system, but now there isn’t have a mature model of Parallel manipulator dynamic and methods of Simulation calculation. In this following passage, aiming at 3PUU parallel manipulator, we establish dynamic model In ADAMS software; design the servo controller in MATLAB and setting to the control parameters. The co-simulation results computer simulation validate the rationality of modeling of electromechanical coupling dynamics and show the optimal control of the mechanism’s displacement and torque of the servomotor by controller.

Abstract: One 203mm drill collar failed infrequently just after 200h of pure drilling time. This paper gives a systematic analysis in consideration of both material quality and loading condition on drill strings. Measurement and inspection were performed on configuration, chemical composition, mechanical performance, metallograghy and micro-fractograghy. It’s thought that the drill collar failure accident was premature fatigue failure accident. Failure reason is the mechanical damage caused by improper manufacture process in the root of thread. Under the effect of fluctuating stress, fatigue cracks originated from mechanical damage position and grew rapidly. When cracks propagated through the wall thickness, drill collar fractured.

Abstract: In order to satisfy the development trend of light-weighting design of large crawler crane, beginning with analysis of the influence of wind load on the performance of large crawler crane truss structure, the numerical simulation of the crawler crane typical truss structure is carried out by fluid dynamic analysis software. Under the limit working condition of wind blowing, the impacts of steady-state wind field and dynamic-state wind field to the performance of truss structure are calculated separately and the coupling effects of various rods of truss structure in the wind field are analyzed. The simulation and calculation results indicate that the wind load calculation method for the crane truss structure in the existing design criterion of crane truss structure is too conservative, which make the self-weight of the truss structures much bigger. Research results in the paper provide certain reference for the light-weighting design of large-scale crawler crane truss structure.

Abstract: According to superposition compression arch structure and the interaction mechanical characteristics of cavern rock, based on limit equilibrium theory, set up reliability analysis model of large-span cavern of a high-stress mine. Using FOSM method determines the reliability index of the large-span and high-stress cavern. By the mean and variance calculations of simplistic variations parameters of construction features, geological investigate and rock mechanics of Jinchuan Mine large-span cavern obtains a suitable jinchuan mine's reliability index formula, and calculates the reliability index()of Jinchuan Ⅲ mine crashing cavern, the minimum value of 1.137. On the assumption that random variables of affecting the stability of the crashing cavern obey normal distribution, and the reliability index()and failure probability()have established relationship. According to the standard normal distribution function can be calculated less than the risk probability()of instability of the structure of 5.87%, that is the stability of the cavern is greater than 94.13% reliability to suffice the stability requirements of the cavern.

Abstract: The stochastic resonance in a bistable system subject to asymmetric dichotomous noise and multiplicative and additive white noise is investigated. By using the properties of the dichotomous noise, under the adiabatic approximation condition, the expression of the signal-to-noise ratio (SNR) is obtained. It is found that the SNR is a non-monotonic function of the asymmetry of the dichotomous noise, and it varies non-monotonously with the intensities of the multiplicative and additive noise as well as with the system parameters. Moreover, the SNR depends on the correlation rate of the dichotomous noise.

Abstract: The effect of time delay and noise color in a time-delayed bistable system subject to asymmetric dichotomous noise and colored noise as well as to square-wave signal is studied. Applying small delay-time approximation, under the adiabatic limit condition, we obtain the expression of the signal-to-noise ratio (SNR) of the system. By virtue of the SNR expression, we find that, the SNR varies non-monotonously with the delayed-time and the correlation of the colored noise. Moreover, the SNR exhibits SR behavior as a function of the strength of the colored noise

Abstract: In the present paper, the current state of magnesium scrap recycling via melt refinement was reviewed and the difficulties confronted in the developing fluxless techniques were highlighted. Then, the working principle of a fluxless technique newly developed in China was briefly introduced followed by chemical and light microscopy investigation of the processing quality of the recycled ingots in comparison with the commercial ingot produced with predominant flux processing to have a first insight into the difference of the two refining techniques. The results indicate that a stable, continuous and cost effective melt refinement can be achieved with the commercial Mg scraps in-house fluxless recycling system.