Applied Mechanics and Materials Vol. 142

Abstract: When tank bottom is detected by acoustic emission method, many corrosion acoustic emission signals can be obtained and adulterated many noise signals, which influence badly the estimation to the corrosion situation of tank bottom. In order to identify acoustic emission sources and disturbance sources without changing the characterization of acoustic emission sources, independent component analysis is used to deal with the denoising of corrosion acoustic emission signals of tank bottom in this paper. In the paper, acoustic emission signals of double exponential model is respectively mixed with white noise signals and stochastic noise signals, and acoustic emission sources and disturbance sources are respectively represented by double exponential model of acoustic emission signals and noise signals, which are independent on statistics, and then FastICA is used to simulation analysis, which is successful to identify acoustic emission signals and white noise signals. The results demonstrate that fastICA is effective to denoise acoustic emission signals.

Abstract: Fracture of coating materials often occurs at or near the interface, while the mechanism and criterion of interface fracture are not clear yet. A molecular dynamics simulation method was introduced to simulate the interface crack initiation, and the relationship between the interface stress and the interface fracture was found. Although a simplified model was applied, the results still showed some intrinsic features that are useful to study the process of interface fracture. At last, an interface fracture criterion was proposed.

Abstract: Effect of ammonium and nitrate ratios (0:100, 25:75, 50:50 and 75:25) on nutritional quality of flowering Chinese cabbage (Brassica campestris L. ssp. chinensis var. utilis Tsen et Lee) with 3 cultivars were studied in hydroponics. The results indicated that, with the increasing of ammonium proportion in nutrient solution, the soluble sugar content in product organ of flowering Chinese cabbage increased gradually, but Vc content decreased gradually. Enhancement of ammonium by 25% or 50% in nutrient solution increased the soluble protein content in leaf significantly, while it increased gradually in stalk with the increasing of ammonium proportion. Free amino acids in product organ of flowering Chinese cabbage were improved significantly by enhancement of ammonium in nutrient solution. Integrated nutritional quality of flowering Chinese cabbage in 25% ammonium enhancement treatment was better than others under hydroponics condition.

Abstract: In order to investigate the effect of defects on rock fracturing under dynamic loads, blasting experiments using PMMA specimens with pre-existing defects were conducted. The defects include holes, pores and small open joints, etc., and they are randomly distributed. In order to verify the experimental results, numerical simulation was implemented. It is shown that under blasting loads, most cracks initiate at pre-existing defect tips, and near free boundary, many cracks developed near defect tips are parallel the free boundary. The numerical results qualitatively agree with experimental results

Abstract: Rock bursts are a main geologic hazard in underground engineering processes, such as mining engineering and tunnel excavation, so it has become an important subject for many researchers and engineers. Photoelasticity, which is a nondestructive, whole-field and graphic stress-analysis experimental technique, is widely used for 2-D and 3-D analysis for getting the information of principal stress difference and principal stress direction of samples. In this paper, the effect of the position and orientation of cracks, which is situating inside the surrounding rock mass of a tunnel, on stress intensity factor (SIF) is analyzed. The results show that crack orientations and the load conditions of tunnel affect stress intensity factors significantly.

Abstract: Coal usually contains many cracks which affect the stability of mining zone. In order to research the fracture mechanism of cracked coal, a special case of three collinear cracks filling with gas is considered. A set of complex stress functions which satisfy all the required conditions are first derived, based on Muskelishvili’s results. The least square boundary collocation method is used to enforce the external boundaries approximately, and the stress intensity factors (SIF) can then be computed according to the related formulae. The value of SIFs for different crack orientations, different crack distance under different loading are calculated. The results shows that the most unfavorable crack orientation is in the 45° angle and the confining stress and the distance between cracks have a considerable effect on the SIF value.

Abstract: In this paper, spinel LiMn₂O₄ was prepared by the solution combustion synthesis using acetate or nitrate salts as raw materials and acetic acid as fuel. The composition and phase structure are determined by X-ray diffraction (XRD) and the electrochemical performance is tested by using a coin type half-battery versus Li⁺/Li. The results indicate that the products prepared from acetate salts have higher purities, higher crystallinities and better electrochemical performances than these of the products prepared from nitrate salts. And for the products prepared from acetate salts, the performance becomes worse with increasing acetic acid ratios. Contrarily, for the products prepared from nitrate salts, the performance becomes little better with increasing acetic acid ratios.

Abstract: To improve the cyclability of spinel LiMn₂O₄, Al³⁺ doped LiAl_xMn_2−xO₄ (x=0, 0.01, 0.05 and 0.10) materials are prepared using a solution combustion synthesis method using acetic salts as raw materials and acetic acid as fuel. Their phase structures are characterized by X-ray diffraction (XRD). Electrochemical performances of the materials are investigated by galvanostatic charge/discharge methods. XRD results reveal that the purity of the samples increases with increasing Al³⁺ content. Electrochemical experiments demonstrate that the charge/discharge cyclability of the LiAl_xMn_2-xO₄ increases with increasing Al³⁺ content. Compared with the pristine LiMn₂O₄, the Al-doped LiAl_xMn_1−xO₄ show the obviously improved cyclability, especially for the sample LiAl_0.1Mn_1.9O₄.

Abstract: Spinel LiMn₂O₄ have been prepared by a flameless solution combustion synthesis, using nitrate and acetate salts as raw materials without any fuels. The effect of ignition temperature on the phase structure, micro morphology and electrochemical performance has been studied. The results indicate that spinel LiMn₂O₄ with single phase can be prepared successfully by the present method at the ignition temperatures of 300-800°C and calcination temperature of 600°C for 5h. The crystallinity, dispersity of the gains and electrochemical performance of the products increase with the decreasing ignition temperatures.

Abstract: In this study, effective dispersion of different amount of multiwall carbon nanotubes was achieved using a surfactant and in combination with the use of ultrasonic energy. The effects of surfactant and surfactant concentration on the plain cement mortar were investigated. Moreover, the mechanical behaviors of the carbon-nanotube reinforced composites were also analyzed. Experimental results indicate that the application of ultrasonic energy is absolutely necessary to produce a satisfactory dispersion of MWCNTs, and there exists an optimum weight ratio of surfactant to MWCNTs. It is found that the proper dispersion of MWCNTs can remarkably improve the flexural strength, compressive strength, and the toughness of the cement mortar composites.