Advanced Materials Research Vol. 800

Abstract: Solar photovoltaic cell demand is great in the whole world and its manufacturing cost is also high. The main reason that slicing cost is too high, because of the low slicing efficiency and large kerf loss.Therefore, many scholars are studying new slicing method in order to reduce the cost. In this paper, we summarize conventional and new slicing method for solar silicon wafer, and think that new slicing method widely apply in photovoltaic industry, which needs to solve some technical problems. At present, multi-wire saw technology still is mainly slicing method in photovoltaic industry.

Abstract: Experimental and numerical simulation researches were presented on dynamic buckling behaviors of cylindrical shell subjected to explosion loading.An account is given of some principal observations made from a series of experiments in which steel cylindrical shells were subjected to central impact by 200g cylindrical TNT dynamite with different distances.By means of an finite element computer code LS-DYNA,the nonlinear dynamic response process of the cylindrical shells subjected to explosion loading were numerically simulated with Lagrangian-Eulerian coupling method. The numerical simulation results were in good agreement with experimental data. The results provide a reference for the design of explosion-resisting structures.

Abstract: Porosity is formed because of the keyhole collapse. The porosity formation is associated with the melt pool dynamics, the keyhole collapse and solidification processes. The objective of the paper is t to investigate porosity formation mechanisms and fluid flow in the melt pool using the volume of fluid method. The results indicate that the formation of porosity in continuous wave keyhole mode laser welding is associated to keyhole collapse, backfilling of liquid metal close the gas exit of the laser welding keyhole, surface tension of the gas/liquid interface play an important role in the backfilling downward to the keyhole right after laser beams left.Keywords: porosity; keyhole; collapse; welding; model

Abstract: The study of LED reliability becomes more and more important with LED widely used in various areas, and accelerated life test (ALT) as an element of reliability test is widely used to predict the lifetime of LED. In this paper, ALTs have been carried out at various current levels and various temperature levels. In the current ALT experiment, three kinds of stressing currents were demonstrated for 1W white LEDs and lumen flux of the tested LEDs were studied, and based on Eyting model, lifetime of the tested LEDs is calculated about 6.86×10⁵h. In the temperature ALT experiment, two kinds of stressing temperature were demonstrated for the same type of white LEDs and lumen flux were also studied, and based on Arrhenius model, lifetime of the tested LEDs is calculated about 7.41×10⁵h. In addition, the color shifting velocity is faster than lumens depreciation velocity was observed in our experiment, which means the lifetime evaluating of white LED should be paid more attention.

Abstract: SiC is one of the most important third-generation semiconductors, which has important application value. Based on the nonequilibrium Molecular Dynamics method, a model of 3C-SiC nanowire is proposed, and thermal transport under different temperatures is investigated. The results show about 200K the thermal conductivity of 3C-SiC nanowire approaches to the peak 7.84W/m.K.

Abstract: Acoustic principle of ultrasonic measurement for stress field was introduced briefly. Longitudinal critically refracted (Lcr) wave was applied to study a non-uniform stress field in high strength 7050-T7451 aluminum alloy. Error sources of testing were investigated as well. The results indicate that ultrasound can be conveniently used to characterize non-uniform stress field with sufficient accuracy but without destruction. The measuring results represent mean stress existing in propagation path of ultrasonic. Stress field mapped by ultrasound has good coincidence with actual stress field. Temperature and coupling are main error sources of testing. As long as temperature maintains invariable, it is easy to characterize stresses with error less than 40 MPa even in different coupling condition and with other artifical variable. The measurement error induced by coupling was tolerable and reduced with increasing stress. This technique will provide a non-destructive method to measure residual stress in structures.

Abstract: Mechanical structure strength analysis of field refueling tank is analyzed and simulated in this paper, A simple and effective mechanical dynamic model is proposed. Stress distribution graph and strain distribution graph of field refueling tank driving in emergency brake or off-road is studied, maximum stress point and maximum strain point is found, theoretical basis of optimization design for field refueling tank is provided.

Abstract: The increase of the strength of gray cast iron is mainly depended on alloying. However, with the improvement of strength, its processing performance will always decrease. So three different gray cast irons are studied in this experiment, including adding 0.1% Nb elements, adding 0.2% Nb elements and adding 0.3% Nb elements, to investigate the Nbs effect to the mechanical performance of gray cast iron, we adopt Dynamic Strain Amplifier to measure cutting force to evaluate processing performance, use Optical Microscope and Electron Microscopy observe each samples organization, explains the relationship between Nbs content and the mechanical and processing performance of gray cast iron from micro-level. Finally, we draw the conclusion: when the Nb comes to 0.3 percent, the appearance of E-type graphite and Nb carbide durum granular will greatly decrease its processing performance.

Abstract: The effects of Y and Gd on the microstructure and mechanical properties of AZ81 magnesium alloy were studied by alloy preparation, microstructure analysis and mechanical property testing. The results show that moderate addition of Y and Gd to AZ61 magnesium alloy can obviously refine grains of AZ61 alloy, and decrease the amount of Mg₁₇Al₁₂ phase. With the increase of alloying elements, the tensile strength and elongation of aged AZ61 magnesium alloy at the temperature ranging of 25°C～175°C rise at first and then drop.When content of Y and Gd is up to 2.7%，the values of tensile strength of the alloy at room temperature and 175°C are up to their maximums, 254MPa and 164MPa respectively, while the elongation of the alloy are 22.9%,18.7% respectively. Y and Gd improve the mechanical properties of AZ61 alloy because of the grain refining strengthening, solution strengthening and the dispersion strengthening.

Abstract: Because the fragility analysis methods used in recent years have some disadvantages to some extent, and there is no relative research report on the seismic fragility of structures based on SVM algorithm, nonparametric analytical method is used in the probabilistic seismic demand analysis, and fragility curves of RC isolated continuous bridge are obtained based on SVM Method. It turns out that the analytical results of SVM Method and Cloud Method are different in the longitudinal direction, matched in the lateral direction, and the results of the former method are greater than the latter one. It is a new and meaningful research that is more efficient than IDA method and also reliable.