Applied Mechanics and Materials Vols. 29-32

Abstract: To strengthen monitoring for plastic debris in the ocean, our paper compared debris distributions of 2 special Garbage Patches (The North Pacific Central Gyre and Kuroshio Current area). And then we developed a computer-based optimal searching model to monitor formation and changes of debris in the oceans. We found that winds belts, currents, and regional human activities along with seasonal climatic variations can influence marine litter patterns and trends in deposition.

Abstract: Hot stamping of quenchable boron steels is a new and complex forming technology integrating metal hot forming and quenching process. In order to gain the Time – Temperature - Transformation (TTT) curves of 22MnB5, the phase-transformation temperatures of boron steel 22MnB5 are measured by DIL 805A/D quenching and deformation dilatometer. According to the expansion curves of phase-transformation at some constant temperatures, the start and finish temperatures of phase-transformation are calculated by using the expansion method and the tangential method. The types of metallographic phases after phase-transformation are judged by the optical microscope and micro hardness. The TTT curves of 22MnB5 are drawn in terms of the results of testing and calculating.

Abstract: White light digital image analysis in frequency domain has the characteristics of whole-field, non-contact measurement. The measuring system of this method is very simple and the coherent light is not demanded. Gray images before and after deformation which are recorded using CCD camera, digitalized and then analyzed by frequency domain correlation arithmetic can be used to obtain the displacement information. This method is used to study the fracture characteristics of concrete and measure the stress intensity factor of I type crack tip. Comparing the experimental results and theoretical values of the stress intensity factor of I type crack tip, the applicability of this method was certified, which shows that this method is very proper to study the deformation and fracture characteristics of concrete.

Abstract: White light digital image analysis in frequency domain is introduced to study concrete deformation. This method has the characteristics of whole-field, non-contact measurement and the simple measuring system and can obtain displacements by frequency domination correlation arithmetic. Displacements of concrete specimen under axial tension are obtained by white light digital image analysis in frequency domain and then strains and Poisson ratio are calculated. Comparing the experimental results and the theoretical values, the error was little and the effectiveness of this method is certified. The applications of different surface features of concrete are studied.

Abstract: In order to improve the precision of BGA solder joints inspection, the cross-section images of BGA solder joints are analyzed based on the 3D X-ray technology. The BGA solder joints or the BGA ball and background is segmented. The features of BGA solder joints defects and decision rules are extracted. And then inspection algorithms in vertical and horizontal cross section are presented. The defects of short circuit, shift, lacking solder, void, warpage and broken circuit can be inspected by the proposed algorithm.

Abstract: The influence of some commonly used inhibitors on the tungsten carbide leaching of the cemented carbide tool was studied by energy spectrum analysis and electrochemical gaging. And the mechanism of the tungsten carbide leaching and be inhibited of the cemented carbide was discussed. The test results showed that when cemented carbide tool were soaked in tri-sodium phosphate and sodium carbonate anhydrous the tungsten carbide in the cemented carbide tool leached out for hydration. And benzotriazole has a good inhibitory effect on the tungsten carbide leaching of the cemented carbide tool.

Abstract: Micro-detonation arc machining (MDAM) is a newly proposed special machining technology for engineering ceramics. To study its working principle is of important significance. By means of high speed video and current signal acquisition system, the shape of micro-detonation arc is observed and the formation course of micro-detonation arc is analyzed. The generation process of ablation pits for Si3N4 and Al2O3 is observed by high speed video. Experimental results show that the generating process of micro-detonation arc can be divided into two phases: spark discharge and stable arc. The diameter of micro-detonation arc increases as working current growing. Si3N4 ceramics decompose and Al2O3 ceramics melts when it machined with MDAM. The materials are removed by synergistic effect of high temperature and intensive impact pressure of micro-detonation arc.

Abstract: The wall material plays an important role for the electron current due to near wall conductivity in Hall Thrusters. A Monte Carlo method combined with a one dimensional steady sheath model is presented and is applied to simulate the electron conductive current due to near wall conductivity for the different channel wall materials of Hall thruster. The simulation results show that the higher the secondary electron emission (SEE) coefficient of the channel wall material is, the greater the electron conductive current is. Based on the simulation, a physical explanation is given from the viewpoint of near wall conductivity. For the channel wall material with low SEE coefficient, the secondary electrons taking part in the near wall conductivity becomes less. In addition, the absolute potential drop in the sheath near the wall increases, which means that the sheath can stop more electrons from colliding with the channel wall. And consequently the electron conductive current due to near wall conductivity is much less. The situation is vice verse for the channel wall material with high SEE coefficient. The simulation results are qualitatively in accordance with the experiments. The results can help to choose and design the wall material of the Hall Thrusters with a high performance.

Abstract: The conceptions of springback anti-couple systems and equations are initially given. By the use of the weighted residual method to the springback anti-couple equations, the springback principles of minimum potential energy and minimum complementary energy are established. Meanwhile, the springback principle of minimum potential energy is applied to calculating springback deformations of a curved beam under the radial and circumferential forces and end bending moments.

Abstract: A two dimension value simulation was carried out for studying the electromagnetic force effect on melting pool in plasma powder deposition process. As the process is a layer-laminated deposition process, the gravity and the fluid motion of molten metal in melting pool during the layer-laminated deposition process without supporting, it will difficult to form complex shape parts. So a new scheme which using the magnetic field to restrict the melting metal flow was proposed. The method designed a restricted equipment of magnetic field in order to prevent and reduce the fluid flow and collapse of the melting pool. Compared with traditional method, as the height of the deposition shape increased, the process restricted with electromagnetic force can make the shape of parts more complex and more accurate. The changes of the electromagnetic force field were simulated with the finite element analysis, while the effects of electromagnetic force on forming process were discussed. Simulation show that the method is feasible and practicable. The electromagnetic force will decrease the post-treatment procedure and could contribute to the process of plasma powder deposition manufacture.