Materials Science Forum Vols. 675-677

Abstract: Increasing demands for miniature metallic parts have driven the application of micro/meso forming process in various industries. The present study focuses on the size effect which appears in the micro/meso scale sheet forming process. Micro/meso scale stamping experiments and finite element simulations incorporating the CMSG plasticity theory are conducted, respectively. It is found that the numerical simulation results, with strain gradient and strain gradient path taken into account, match the experimental results better than those of conventional simulation method.

Abstract: High quality magnesium oxide (MgO) single crystals have been grown by an arc-fusion method. Due to the hostile environment for observing the process occurring in the inner zone of the furnace, direct measurements on the arcs by conventional diagnostic method are practically impossible. Moreover, it has been proved that the control of the temperature field of the whole system is crucial to grow high-purityMgO single crystals with large and super-large sizes. However, very few studies have been carried out to investigate the correlation between the thermal behavior and MgO single crystal growth in the furnace. In present study, a transient 3D finite element model has been developed to depict melt/crystal interface and to find out the determining factors that affect the crystal growth rate and the growth direction. It is shown that the model gave a good description of the bath shape which agrees well with that of the solidified MgO in experiments. By the transient analysis, the trend and time delay of the temperature variation on the shell were also predicted.

Abstract: Self-pierce riveting (SPR) technology offers an alternative to resistance spot welding (RSW) for joining sheet materials. It has been found that the SPR technology produced a much stronger joint than the RSW in fatigue test. For efficient design of SPR structures, the knowledge of dynamic characteristics of the SPR beams is essential. In this paper, the free transverse vibration characteristics of single lap-jointed cantilevered SPR beams are investigated in detail. The focus of the analysis is to reveal the influence on the natural frequency and natural frequency ratio of these beams caused by variations in the material properties of sheet materials to be jointed. It is shown that the transverse natural frequencies of single lap jointed cantilevered SPR beams increase significantly as the Young’s modulus of the sheet materials increases, but change slightly corresponding to the change in Poisson’s ratio. It is also found that the material density of the sheets have significant effects on the free transverse vibration characteristics of the beams.

Abstract: The interaction force and the environments uncertainties are the most challenges for robotic material removal process. The conventional constant force control methods for the deburring process have the inherent characteristic of leaving the deburred surface as an imprint of the original. A process force model considering the burrs variation is presented to predict the contact force in robotic machining process. A self-tuning fuzzy strategy is adopted to implement the on-line compensation for the static error caused by the traditional impedance controller. The fuzzy controller is adjusted by an updating factor to select the most appropriate fuzzy rule set based on the measured performance results. Simulation results show efficacy of the proposed method in robotic machining process, and the control performance is better than that of a traditional impedance controller.

Abstract: The simplified method called Inverse Approach (I.A.) has been developed by Batoz, Guo et al.[1] for the sheet forming modelling. They are less accurate but much faster than classical incremental approaches. The main aim of the present work is to study the feasibility of the I.A. for the axi-symmetric forging process modelling. In contrast to the classical incremental methods, the I.A. exploits the known shape of the final part and executes the calculation from the final part to the initial billet. Two assumptions are used in this study: the assumption of proportional loading for cold forging gives an integrated constitutive law without considering the strain path and the viscoplasticity, the assumption of contact between the part and tools allows to replace the tool actions by nodal forces without contact treatment. The comparison with Abaqus shows that the I.A. can obtain a good strain distribution and it will be a good tool for the preliminary preform design.

Abstract: The self-diffusion coefficient of Cu in Sn-1.5wt.%Cu and Sn-2wt.%Cu lead-free solders was investigated using molecular dynamics simulations based on a modified embedded-atom method from 503 K to 773 K. Then the viscosity of the solders was calculated using the selfdiffusion coefficient values, and the results were in good agreement with the experimental data. Two segments, a low-temperature zone and a high-temperature zone, were found on both η–T and lnη–1/T plots, where η is the viscosity and T is the absolute temperature. Through analysis, we infer that the viscosity mutation was attributed to the remarkable structure transition.

Abstract: To explore a novel sensor to detect the presence of nitrogen dioxide (NO2), we investigate reactivity of boron-doped (B-doped) single-walled (8,0) silicon carbide nanotube (SiCNT) with NO2. Based on density functional theory, the structure and electronic properties of the B-doped SiCNT with and without the adsorption of NO2 molecule have been calculated. Results show that a stable adsorption between the nanotube and the gas molecule is formed and the conductivity of the SiCNT is improved obviously. B-doped SiCNT is expected to be a potential candidate for detecting the presence of NO2.

Abstract: This paper presents a method for calculating the temperature field distributions for MgO single crystal furnace. Finite element method (FEM) had been used to carry out the temperature field distributions of MgO single crystal furnace in terms of its energy consumption. Then fuzzy model of the furnace was developed using adaptive neuro-fuzzy inference system (ANFIS), for carrying out its temperature field analysis. Performance was evaluated by comparing finite element model with fuzzy model and good correlation was achieved between them.

Abstract: Using Y2O3, Mn(CH3COO)2·4H2O as raw materials and glacial acetic acid as solvents, YMnxFe1-xO3 precursors (x= 0, 0.05, 0.1, 0.3, 0.5) have been prepared under 80°C water bath conditions. Perovskite YMnxFe1-xO3 samples were achieved after calcination over 900 °C for 4 h. Structure of the samples was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Ultraviolet obvious diffuse reflection(UV-vis DRS), and Field-emission scanning electron microscopy (FESEM). Photocatalytic activity of the samples was also investigated. Results showed that all the samples with stable perovskite structure had high light absorption in visible-light region, suggesting good visible light harvesting. SEM image showed that the samples were sponge-like and porous agglomerates. Photodecoloration activity of 100 mL Rhodamine B (10 mg/L) was 16~56 % under illumination for 150 min. Oxygen vacancies of the perovskite may explain the high activity of x = 0.1 sample.

Abstract: The optimal preparation condition of V2O5/TiO2 catalyst was investigated by the orthogonal experimental method. Five factors were chosen including A(molar ratio of NH4VO3 to oxalic acid),B(aging time of solution),C(active component content),D(impregnation temperature) and E(impregnation time). Every factor had four levels. The levels of A were1:2, 1:1, 3:2 and 2:1. The levels of B were 12h, 14h, 16h and 18h. The levels of C were 2%, 4%, 6% and 8%. The levels of D were 45°C, 55°C, 65°C, 75°C. The levels of E were 2h, 3h, 4h and 5h.The orthogonal experiment table was L16(45). Then the de-NOx rate of V2O5/TiO2 catalysts was tested in SCR catalytic reactor. The results showed that the influence of chosen factors decreased in the following order: C> B> E> D> A. The optimal plan of preparation experiments, obtained from the orthogonal experiment, is C3B1E3D3A4. So the optimal condition of preparation experiments are that active component content is 6%，aging time of solution is 12h，impregnation time is 4h，impregnation temperature is 65°C，molar ratio of ammonium metavanadate and oxalic acid is 2:1.