Applied Mechanics and Materials Vols. 300-301

Abstract: The dead-time effect of the SVPWM inverter was analyzed as well as its effect on the control system performance (distortion of phase voltage and zero-current clamp phenomenon of phase current, etc).Then, basing on the analysis about the generation of the dead-time effect, the error voltage vector compensation strategy was raised. In order to verify the correctness and reasonableness of the compensation strategy, simulation system was constructed in use of Matlab/Simulink software to implement analysis and research. Simulation results show that the zero-current clamp phenomenon of phase current was basically eliminated after using the dead-time compensation. Then spectrum analysis was made for the phase current waveform, which showed that the compensation strategy weakened the fifth and seventh harmonic waveform brought by the dead for the inverter, significantly improved sinusoidal and system control performance of the phase current, and proved the theoretical correctness and experimental feasibility.

Abstract: In this paper, we consider a class of elliptic equation on unbounded domain. By the variational method, we prove the existence of solutions.

Abstract: In order to reduce the influence of frictional interference and measurement noise on stabilized platform tracking performance, disturbance observer (DOB) is applied to platform servo system. In view of the non-ideal performance of classical disturbance observer about suppressing measurement noise, a novel improved DOB which uses an additional control signal to compensate system outputs is proposed based on the structure of classical DOB, and robust stability of the improved DOB when existing model perturbation is analyzed in detail. Simulation results show that the improved DOB can suppress external disturbances and model perturbation well, and the suppression performance of measurement noise is improved, too.

Abstract: Socket welds are widely used in nuclear power plants. According to industry experiences, vibration fatigue of socket welds is becoming one of the major ageing issues. It is very important for the operating engineers to monitor the vibration condition and detect the damage before leak occurs. This paper studies the damage identification technology applying wavelet transform method. Small bore pipes with socket welds are installed on the vibrating table and vibrate at the frequencies that near its first natural frequency. The acceleration response signal is acquired and decomposed by wavelet method. The energy of decomposition signal shows a suddenly variation when crack occurs. From this study, a parameter that is sensitive to vibration fatigue is defined and has the potential application value in the nuclear power plants to identify the vibration fatigue damage.

Abstract: For obtaining fatigue limit and dealing with censored data, the" pair- life -weighted” is proposed in this paper. According to the fatigue testing of TA15 electron beam welded specimens, conventional methods and two methods in this article are used separately to calculate the fatigue limit and lognormal distribution parameters of the lives at different stress levels, and C-P-S-N curves are obtained and their corresponding mathematical expressions of 12 groups under 2 Confidence and 6 reliability are expressed as a three-parameter model. The results show that the" pair- life -weighted method " is in good agreement with the traditional method, when the lives have a difference of 3 times at the same stress, the fatigue limit only have a difference of 0.5%, it is the further evidence of the practicability in engineering about the traditional method.

Abstract: A model of gear contact has been established based on Hertz theory in this thesis, Analysis of non-standard gear contact fatigue life test process . For ha* take 1,1.15,1.25 and c* take 0.25,0.5 respectively ,the gear generates contact fatigue failure, then calculate the meshing ratio under different tooth high coefficients, and gear pairs state with fatigue testing time by the finite element method and orthogonal test. These data are compared with the results of specific experiments verified. They description that tooth height coefficients and headspace coefficients change have a great impact on gear contact fatigue life.

Abstract: The nonlinear vibration analysis related to viscoelastic damper is investigated for the new whole-spacecraft passive vibration isolator. The stepped sinusoidal sweep test is performed and the results reveal the nonlinearity of the system. The nonlinear motion equation is developed. The frequency response equation is derived by the method of harmonic balance. The experiment of various excitation levels are carried out contrasting with numerical simulations. The nonlinear influence factors to the vibration isolation system are argued and the identification results explain the effect parameters on the performance of the vibration isolator. The research work is of significant implications for the analysis and design of passive vibration isolator for a wide range of practical applications.

Abstract: The averaging method has been applied to calculate the critical conditions of parametric resonance instability of the first order mode shape of clamped-clamped and pinned-pinned pipes conveying fluid. The influence of gravity factor on parametric resonance of pipe conveying fluid, with different supporting forms and different flow velocity, has been studied based on the comparison results of gravity factor being considered and neglected. It is concluded that gravity factor has a greater influence on parametric resonance region of pinned-pinned pipe than the one of clamped-clamped pipe, and, at a higher flow velocity, gravity factor is more influential to both pinned-pinned pipe and clamped- clamped one.

Abstract: With ever increased demand for reduced sizes and increased complexity and accuracy, traditional machine tools have become ineffective for machining miniature components. Typical examples include dental implants, the parts used in mechanical watch movement, and the parts used in medical endoscope. With complex geometry and tight tolerance, few machine tools are capable of making them. This paper introduces our PC-based CNC Turn-Mill Machining Center. It has 5 axes, an automatic bar feeder, an automatic part collection tray, and a tool changer. In particularly, it has a special synchronization control algorithm that gives not only higher accuracy but also ease of use. In addition, to improve the accuracy, the software based volumetric error compensation system is implemented. Based on the experiment testing, the machining error is ± 3 µm in turning, ± 7 µm in milling and the maximum profile error is less than ± 7.5 µm in gear hobbing.

Abstract: The effect of multi-walled carbon nanotubes (MWCNT) on the elastic modulus of MWCNT/epoxy nanocomposites was investigated. Carboxylic acid-functionalized MWCNTS (MWCNT-COOH) were obtained by oxidation pristine MWCNTs via sonication in sulfuric-nitric acid. Epoxy-based nanocomposites reinforced with MWCNTs with and without functionalization were prepared. In this work, the elastic modulus of MWCNT reinforced nanocomposite was determined by free vibration test. Experimental results showed that functionalized MWCNTs improved the dispersion of MWCNTs in epoxy matrix leading to the enhancement of elastic modulus compared to those containing MWCNTs without functionalization. Nanocomposites prepared with 1 wt % of MWCNT-COOH exhibited 44 % increase in Young’s modulus.