Applied Mechanics and Materials Vol. 470

Abstract: Five groups of vibration experiments were carried out on the 6.8 grades and M20 bolts and nuts that used on transmission tower. The test result shows that the basic way to improve the anti-loosening property was increasing the initial preload. Both increasing initial torque and appending lubrication can obviously increase the initial preload, however appending lubrication may reduce it's anti-loosening property under the situation of same preload. In the vibrating process the second stage plays a decisive role for anti-loosening property, it can be expressed as reduced rate “K” of the preload.

Abstract: A dynamic model of seven degree of freedom for the vertical vibration of stand rolls system in a cold tandem mill is developed by Kinematics Theory. According to the actual parameters of a factory six-roll cold rolling mill, the influence of natural frequency and modes for rolling process is analyzed. It finds that the third-order and the six-order natural frequency play a role key in vertical vibration system. Combined with energy distribution of each part and flexibility of the modes analysis for vertical vibration system, it can avoid resonance of rolling process and optimize the parameters of stand rolls system by adjusting structural size appropriately. The above mentioned results have provided a reference for further research on Kinematics and structural optimization of six-roll cold tandem mill.

Abstract: The research object is 40Cr shaft parts after quenched and tempered. Optimize the main process parameters working pressure, frequency and amplitude of ultrasonic finishing. It is obtained that the various parameters influence the surface roughness of the machining samples and the optimum technological parameters combination which is consistent with experimental results. Using the SPSS software to analyze the results, obtained the process parameters impact trend of the postprocessing roughness. Contrast groups of test data, the best result was reduced by 98.4% compared with the initial roughness , reached the Ra0.04μm.

Abstract: The fatigue tests with 16 hours hold time have been conducted for two rotor steels, 1CrMoV and 2CrMoNiVW at 550°C to investigate their creep-fatigue interaction behaviors, as well as those without hold time for contrast. And two life prediction methods are used to correlate the present creep-fatigue life data. It is shown that a significant reduction in fatigue life is observed with hold time in tension, and it is also observed that 1CrMoV steel exhibits a higher creep-fatigue life than 2CrMoNiVW when strain hold time is 16 hours, and 2CrMoNiVW seems to be more sensitive to hold time influence. In addition, both methods could give satisfactory creep-fatigue life predictions, but with their own limitations.

Abstract: Electro-arc machining is similar with traditional electrical discharge machining (EDM) while the pulse duration of electro-arc machining is longer than that of EDM. The longer discharge was named arcing, and the arcing could lead to high material remove rate (MRR) and low tool wear ratio (TWR). Processing factors including discharge medium, tool polarity, tool material, voltage and rotational speed were chosen as input parameters on MRR and TWR. Taguchis method was used to evaluate their effects. All of the five processing factors had effects on MRR and TWR. The effects and the mechanism are also discussed.

Abstract: The basic hypothesis of this article focuses on the study changes in the tool wear during drilling of cast iron GTW 35-04. The problem of drilling holes with diameter D=5 to 10 mm resides in the fact that 40 % of these holes do not comply with prescribed requested requirements. This article presents the results of experiments focusing on the study of the damage process in helical drills with diameter d=10.0 mm when drilling into the cast iron GTW 35-04.

Abstract: The vibration modals and harmonic responses of the dual ball screw-driven feed system in Z direction are analyzed by the software ANSYS. In this paper, the equivalence of characteristics of fixed and rolling joints is emphasized, while the influence of joint faces on the dual ball screw-driven feed system is analyzed. In addition, the FEM results of spindle and spindle box connecting the feed system are compared with the modal testing value. The results show that the relative errors between corresponding order natural frequency and the test results are within 10%, which verified the accuracy of the modeling method, and the influence of combination on the analysis of the ball screw feed system can't be ignored. Depending on the above, weaknesses of dual ball screw-driven feed structure is found out, which provides the basis for structural optimization.

Abstract: This article touches on the problem that the shock occurs on support at the time of violent vibration and deformation failure of the surrounding rocks. According to the buckling principle, a thin-walled energy-absorption component is designed with special shape applied to a new roadway anti-impact and energy-absorbing hydraulic support in order to relieve excess load impact and injuring and damage by itself and the traits abdicating deformation process and when impact of surrounding rock occurring suddenly, thus preventing support system from the serious damage caused by rock burst. In the theory, simplified energy-absorbing component capacity and energy-absorption formula are obtained by the theory analysis, the effect of energy-absorption curve and the buckling deformation mode are obtained in the quasi-static compression test, results are almost the same with simulation and provide certain reference for the optimization design of support.

Abstract: The concept of DODF and other two evaluation indices based on DODF were proposed. Based on the optimal preview acceleration driver model, the effect of driver model parameters on the performance of driver-vehicle-road closed-loop system was studied by the closed-loop system simulation. The results show that the preview time of a driver who has good driving habits should be always larger than a certain value T_P0, the increase of both nerve delay time t_d and muscle lag time T_h lead to the increase of T_P0, and t_d has more effect on T_P0 than T_h does. The increase of both t_d and T_h lead to the decrease of DODF, and t_d has more effect on DODF than T_h does. Furthermore, the increase of both t_d and T_h also lead to the increase of both tracking index J_EM and driving load index T_CM, t_d has more effect on J_EM than T_h does, and T_h has more effect on T_CM than t_d does.

Abstract: This paper is concerned with the capacity of ad hoc networks employing pure ALOHA medium access control (MAC) protocol under the effect of different transmission power levels and variable data rate control. The data rate of a certain link is related to the signal to interference plus noise ratio (SINR), and SINR is, in turn, related to the transmitted power and link distance. The increasing power conducts a high data rate, resulting in the high interference of networks. Consequently, the optimum power that yields maximum network throughput is a tradeoff between transmission rate and network interference. Mathematical model analysis for the ad hoc network capacity are presented in the paper. A revised expression to the approximate calculating of the capture probability in networks is proposed.