Applied Mechanics and Materials Vols. 29-32

Abstract: A three-dimensional finite element model of helix double-edge cutting is developed to study the ending milling process of titanium alloy Ti6Al4V. Several mechanics models of milling process, such as material constitutive model, friction model and heat transfer model, are implemented to improve finite element simulating accuracy. A milling force experiment is carried out, and a good agreement between simulation and experimental value is achieved, which proved that the finite element model presented in this paper is correct. Using this finite element model, chip formation and cutting temperature are simulated and analyzed. This work will be a base for process parameter optimization, tool’s optimization selection and design during high speed milling of difficult-to-cut titanium alloy.

Abstract: Theoretical analysis and material experiment are employed to study the “single factor” material model. Based on the dislocation theory, an analysis shows that material model is deeply affected by temperature. By the least squares best fit to experimental data, material parameters are found. Experiment curves analysis and material parameters comparison show that the material parameters of “single factor” model of Mo-Cr cast iron are temperature dependent. Using the mathematical mapping between material parameters and temperature, the “single factor” material model of Mo-Cr cast iron is established, which is proven to be right by comparing with experimental measurements. This work provides a useful insight for understanding the material model and helps to develop further finite element simulation of high speed cutting process of Mo-Cr cast iron.

Abstract: Study on wind-resistant performance of one special-shaped long-span arch bridge is carried out using a full-bridge aeroelastic model with a scale of 1:66 in wind tunnel test. The tests on vortex-induced vibration (VIV for short), buffeting and aerodynamic stability of both bare arch and full-bridge are comprehensively conducted in smooth and turbulent flows with attack angle of -3º, 0º, 3º, and yaw angles ranging from 0º to 180º with a step of 15º. The results show that the first-order symmetric VIV of vertical bending appears on the bare arch in smooth flow with attack angle of -3º, 0º, 3º, and yaw angle of 0º, 5º. The maximum amplitude of VIV at 1/4 section of the bare arch is close to 30cm, higher than the corresponding value at the crown section. No stable VIV is observed on full-bridge model tests in both smooth and turbulent flows. For full-bridge model in turbulent flows, both means and standard deviations of girder torsional displacement at 1/2 and 1/4 sections are very small, which prove that the bridge integral torsional stiffness is significantly improved due to the 3-D cable-support system. The bridge possesses good aerodynamic stability for both bare arch and full-bridge service states.

Abstract: A comprehensive study of force measurement test in wind tunnel is conducted for the streamlined deck model of Dalian Cross-sea Bridge scheme. The factors, including stacking load in erection, vehicles arrangement, central slot and so on, are analyzed in terms of the influence of the three-component coefficient in the way of microscopic mechanism. The stall angles under different working conditions are also investigated. The results show that stacking loads and vehicle arrangement barely have any impact on the three-component coefficient, which can be neglected approximately; lift and pitching coefficients decrease for the slotted deck, and the slot width has little influence on the aerostatic coefficients; bridge railing, stacking loads and vehicles change the flow separation and re-attachment around the deck, increasing the turbulence intensity, leading to the fluctuation of stall angles.

Abstract: By using FEM method, the natural frequencies of the super-long steel and CFRP cables with possible engineering parameters have been comprehensively studied. The error and limitations of cables’ natural frequencies theoretical calculation formula have also been analyzed. The results show that: Theoretical formula results are more approximate to out-plane frequencies of the cables. In a symmetric mode, out-plane frequency is lower than in-plane frequency, whereas in an asymmetric mode the situation is reversed. The difference between out and in-plane frequencies appear most in the first-order mode. The difference between out and in-plane frequencies is more obvious for cables with low stress, small inclined angle, long length with big sag and strong nonlinearities. The nonlinearities of CFRP cable is relatively slight for its lightweight and high strength. Out and in-plane frequencies are almost identical, and the theoretical formula is applicable to CFRP cables.

Abstract: Nanoparticles have been used with polymer to make composites having remarkable properties. An attempt was made in this direction, in order to enhance the mechanical and tribological properties of nanocomposites. In the paper, the polytetrafluroethylene (PTFE) polymer-based nanocomposites filled with serpentine (SPT) and reinforced with different nanoparticles such as nano-β-carborundum whisker (β-SiCw), nano-copper and nano-TiO2 were prepared by using cold briquetting and hot-press sintering technologies. Also, the mechanical performances of these nanocomposites were studied. The quasi-static tensile experiments and dynamic mechanical thermal analysis (DTMA) were carried out. The results obtained showed that the mechanical properties of these nanocomposites stronger depend on the variety of nanoparticle. Stress-displacement and stress relaxation curves indicate that theses composites are typical viscoelastic materials. These research findings are believed to be helpful for providing practical guide in applications.

Abstract: The tribological tests were conducted on several PTFE/nano-EG solid self-lubricating composites filled with different nano-particles such as nano-Al2O3, nano-copper, nano-SiO2 and nano-TiO2. The Friction coefficient, wear rate, worn surface morphology and transfer film were studied. It was found that the present filler additions can remarkably increase wear resistance in all composites researched in the paper. The friction coefficients of these composites were lower than that of pure PTFE. The experimental results indicate that the enhancement effect of nano-particles effectively improved anti-friction and wear resistance of these composites. The highest wear resistance was found for composites containing (a) 10%nano-EG+10%Al2O3, (b) 10% nano-EG + 20% nano-Cu and (c) 10%nano-EG+nano-SiO2. Scanning electron microscopy (SEM) and optical microscope (OM) were utilized to examine the worn surface of PTFE-based composite and transfer film generated on counterface. Also, the dominant wear mechanisms and mode of failure were studied.

Abstract: A one-dimensional mathematic model is presented which describes pressure fluctuations behavior of liquid-filled pipes. The model is based on conventional two-equations water hammer theory. Here is multi-water-hammer occurring simultaneously and coupling together. The differences are obvious when taking into account coupled water hammer and just single water hammer in Fluid pipe system by comparing the numerical simulation. The pressure characteristics located where water hammer takes place is investigated by numerical simulation and experiment. Then the factors of influencing on the coupled water-hammer pressure and frequency are considered, the result shows that system parameters effecting on it are critical and should be detailedly analyzed.

Abstract: The control demand can not be satified by general PID algorithm because of time-change, nonlinear, uncertainty of controlled parameters in control process of the resistance-heated furnace. Based on regulative fuction of bilogic immune feedback response and characteristic of overhang nonlinear fuction with fuzzy discursion, and combining the advantages of CMAC(Cerebellar Model Articulation Controller), the CMAC-Fuzzy Immune-PID control strategy is applied to temperature control system of the resistance-heated furnace. Simulation study results show that control systems based on this method can attain high quality, is capable of adapting itself to variations of the control object’s parameters, and is featured by strong robustness and self-adaptability.

Abstract: Numerical Simulation of oscillating flow over a circular cylinder is calculated when the Reynolds number is 100. The space-time finite element method is used to solving the two-dimensional incompressible Navier-Stokes equations. Considering the oscillating flow over a variation of perturbation amplitudes and frequency ratios, the trends of lift coefficient with amplitude and frequency ratio are compared respectively. Besides, the FFT of the lift coefficient curves are analyzed. There is a suddenly change in main frequency and second frequency when A=0.1. The excited frequencies of lift coefficient are discussed, which could be the combination of vortex shedding natural frequency and perturbation frequency, such as |fe－f0|, fe, 2fe－f0, fe＋f0, 2fe＋f0, etc.