Applied Mechanics and Materials Vols. 152-154

Abstract: In this paper, recent advances in design and fabrication of a direct methanol fuel cell (DMFC) stack are presented. DMFC fuel cells are viewed as one of the most environmentally friendly energy conversion system due to high theoretical electrical efficiency for portable application. These advantages are mainly depends on overall system design and especially on stack operating performance. In order to increase the performance of the overall system, design criteria of a DMFC stack has been considered. A DMFC stack with optimum flow field, flow direction, uniform pressure drop and flow distribution has been constructed. Scale effects respect to the number of cells are tested on single cell, short stack and stack by a homemade test bench. The results are shown the scale effect respect to the number of cells is ignorable.

Abstract: Fixtures are used to locate and hold workpieces with locators and clamps. As well as having a locating function, fixtures must also ensure that the dimensional quality of the manufactured workpiece can be achieved. Inaccuracies in fixture’s location scheme result in a deviation of the workpiece from its nominal specified geometry. A “multistage” machining process refers to a part that is machined through different setups. At multistage machining, the errors of pervious stages are transferred to next stages. In this paper, an analytic model is developed to integrate the errors in each stage and accumulated error of pervious stages. This model has great potential to be applied toward fault diagnosis and process design evaluation for the multistage process. A mathematical model is developed by the kinematic analysis of the fixture using Jacobian matrix and homogeneous transformation matrix (HTM). The effectiveness of the resultant deviation model is verified by example.

Abstract: The effect of foam fillers on the impact behaviour and energy absorption of an aluminium tube is investigated. Both experimental test and computational simulation are employed in current study. For comparison, hollow tubes and foams are also tested, respectively. Foam filler is found to be ineffective in increasing the crushing loads of the composite tubes over the simple superposition of the crushing loads of hollow tube and foam. Also, foam filler increases the tendency for the concertina mode of folding. The foam fillers of tubes additionally result in increasing the SAE values over those of hollow tubes.

Abstract: Microstructure and hardness property of AgCd alloy internally oxided at 973K for 1 h - 24 h with O2 atmosphere of 3 atm was investigated. Band typed CdO phase was formed at grain boundaries, and particle typed CdO phase was formed at grain interior. In this alloy, it was found that oxygen adsorpted at surface diffuses to interior through grain boundaries, and it subsequently diffuses into grain interior during internal oxidation. No Ag exduation was found in this alloy. The thickness of oxidized layer increased with increasing holding time at given temperature. Hardness of the oxidation zone was 125 ± 5 Hv, which value is higher two times than that of the oxidation free zone. The higher hardness of oxided region than the oxidation free zone was attributed to the dispersion strengthening by CdO particles.

Abstract: The triad sequence distributions of -EEE-、-EEP-、-EPE-、-PEP-、-PPE- and -PPP- of Ethylene-Propylene Rubber (EPR) has been determined by infrared spectroscopy (IR) combined with 13C NMR and partial least squares (PLS) chemo metric algorithm. The triad sequence distributions obtained by 13C NMR was used as reference date. PLS regression models of the sequence distributions of EPR have been developed by MIR range. The wave number range of IR was 1300~600cm-1 and the spectra were pretreated through smoothing and second derivation. The results showed the sequence distributions predicted by models were consisted with the data from 13C NMR. The triad sequence distributions of EPR could be fastly analyzed by IR models.

Abstract: Fluid flow fields of molten steel were calculated under the different setting of flow control device in the tundish, and the characteristics of flow were investigated by residence time distribution curves (RTD). The results show that the response time and peak time are small without the flow control device installed in the tundish. A suitable design of flow control device could extend the mean residence time of molten steel in the tundish, and increases the volume of piston-type flow zone with decreasing the volume of dead zone. It is found that the effect of flow control adopting turbulence inhibitor 2# and dam is the best. The volume fraction of the dead zone is reduced from 54.19% to 16.51%, and the proportion of dead zone becomes much lower. The dominant role of the dead zone has been replaced by that of the piston-type flow zone. A satisfactory effect of flow control could be achieved by adopting wall 3# if a turbulence inhibitor is not available, and the volume fraction of the dead zone is decreased to 24.32%.

Abstract: Springback is an inevitable phenomenon while the load is released due to the elastic property after tube bending. This leads to an increase in the radius of curvature and elongation by plastic deformation, a reduction in the bending angle of the bent tube, a decrease in dimensional accuracy and fits with others difficulty. By elastic–plastic finite element methods (FEM), a reasonable simulation model for thin-walled tube bending is established to define the relationships between process parameters and springback angle, plastic deformation. With 210 kinds of models, the results show that: 1) Springback angle and plastic elongation of bending tube are related to bending angle, bending die diameter and tube thickness. 2) Controlling functions for plastic elongation and springback angle in bending tube process are given, which is verified by tube bending experiments.

Abstract: Ultrasonic levitation system based on Near Field Acoustic Levitation is investigated in this study. A disc is levitated at a height much smaller than the acoustic wavelength where NFAL effect is dominant. A high-order analytical and numerical study on the levitation force induced by gas squeeze film is performed. By taking into account the modal solution on the vibrator whose disunity of the surface displacement can not be ignored, detailed boundary condition of gas squeeze film can achieve a high accuracy in final calculations of time-averaged pressure distribution, load capacity and stiffness of the system. A finite element analysis is compared with analytical solution. By discussing NFAL behavior in gas squeeze films, explanation of essential levitation characters in flexural vibrators is presented, which is important for future study on wafer’s non-contact transportation based on acoustic levitation.

Abstract: The uses of Titanium alloys have largely been increased due to the benefits which are very substantial in some specific areas. Their applications are not only limited to in aerospace industries and biomedical implants but also widely introduced in marine and automotive industries. Yet the optimum cutting conditions for those materials are still under investigation. Ti-alloys are in the group of difficult-to-machine materials due to their poor machinability. The main reasons behind their poor machinability are high chemical reactivity, low modulus of elasticity and low thermal conductivity. Here in this paper a number of literatures related to optimization of machining parameters are reviewed and the problems related to machining of these Ti-alloys including their effects are summarized.

Abstract: Based on the Kirchhoff large deformation theory, the post-buckling behavior of right movable simply supported FGM beam subjected to non-conservative forces and in-plane thermal loading was analyzed in this paper. The temperature-dependent and spatially dependent material properties of the FGM beam were assumed to vary through the thickness. The nonlinear governing equations of FGM beam subjected to a uniform distributed tangential load along the central axis and in-plane thermal loading were derived. Then, a shooting method and Runge-kutta method are employed to numerically solve the resulting equations. The post-buckling equilibrium paths of the FGM beam with different parameters were plotted, and the effects of non-conservative force, temperature, gradient index of FGM on the post-buckling behavior of right movable simply supported FGM beams were analyzed.