Abstract: As an effective computational method, the numerical simulation of welding processes has been widely used in evaluating welding temperature fields and residual stress distributions. In the numerical simulation process, the selection of the welding heatsource model and the confirmation of model parameters will directly affect the accuracy of the calculation and the evaluation results. Some heat-source models commonly used in numerical simulations of the arc welding process were surveyed in this article; advances in their development were introduced, and their characteristics and applicability were analyzed. As basic heat-source models, the Gauss surface heat-source modes and double-ellipsoid-volume heat-source model have been widely used in the numerical simulation of arc welding for workpieces with a relatively small size and a regular welding trajectory, and the calculation results have been demonstrated to be accurate. In the numerical simulation of arc welding processes for large and thick workpieces welded using multi-layer or multipass techniques and for workpieces with a complex welding trajectory, the simplified heat-source model and temperature-substitution heat-source model are chiefly applied, and the calculation efficiency and precision can be well balanced. The heat source of multi-wire arc welding is comparatively complicated, and the superposed model of modified double-ellipsoid-volume heat-source models can ensure a certain accuracy of the calculation results. The combined heat-source model is more flexible in the shape description of the molten pool and has advantages in the numerical simulation of arc welding with deep penetration. The all-around induction and analyses in this article are expected to provide valuable reference and guidance for the selection of a heat-source model and for confirming model parameters in the numerical simulation of arc welding processes.
Abstract: In the loess plateau, shallow loess landslides are especially widespread and frequent geological disasters, causing serious casualties as well as huge property damage. Although two-dimensional deterministic models are widely applied to assess the stability of shallow landslides, they could not sufficiently consider the three-dimensional spatial variation of geotechnical property, layering configurations and groundwater. It might not conform with the actual situation of slope stability. Therefore, the three-dimensional deterministic model with considering complicated slope situation has the great significance to acquire the results that are more accordant with the actual situation. At the same time, it will exercise a profound and far-reaching influence to effectively mitigate landslide disasters. This paper takes the three-dimensional deterministic model Scoops3D to evaluate its adaptation and reliability of predicting shallow loess landslide stability. Firstly, the sensitivity analysis of model calculating parameters indicates that the most influential parameters on accuracy of safety factor are cohesive force, sliding direction of visual angle and the weight of grids, so it could guide to acquire the detail key input parameters. Then, the different resolution digital elevation models (DEMs) and geotechnical parameters are selected and used to predict the stability of shallow loess landslides in the typical gully and ridge physiographic region by using the Scoops3D. Comparing the calculated results with the detail inventory of point landslides and facial shape landslides shows that this model has a high accuracy in predicting shallow landslide stability. At the same time, the inventory of point landslides may be more suitable to model verification than facial shape landslides. Finally, the confusion matrix and the success rate curve are used to examine the reliability of predicted results that based on different resolution DEMs. The results prove that this model has a good adaptation to predict the stability of shallow loess landslides in the selected study area. Meanwhile, it could obtain reliable prediction accuracy with the high-resolution DEM data.
Abstract: Rainfall, especially in rainstorm conditions, is one of the major factors considered in simulating landslides. Landslides often occur on the southern slope of Washan stope in Nanshan iron mine as the slope has increased in height and steepness. To determine the influence of rainfall on slope stability, the southern slope of Washan stope was monitored dynamically by MSR300 radar system for four years in real time. Based on data on rainfall and slope deformation, the slope deformation law between rainfall and rainfall intensity was analyzed. The stages of a landslide were classified by taking a landslide on the southern slope of Washan stope as an example. The deformation displacement and speed of this slope as well as the duration subjected to heavy rainfall were generalized. Then, the instability model and warning threshold were established. The results show that the slope deformation is positively correlated with rainfall in accordance with the power function. The slope deformation velocity is in good agreement with the rainfall intensity. Furthermore, the landslide generally occurs after maximum rainfall intensity. The landslide stages were classified into three, namely, initial deformation, stable deformation, and accelerated deformation. The warning threshold of displacement was 20 mm within 6 h and 30 mm within 12 h. The speed threshold was 1.5 mm·h-1 within 6 h and 2.5 mm·h-1 within 12 h. The landslide curve on the stope was highly similar to geotechnical non-steady creep curve. "Sharp convex"and"step jump"phenomena occurred on the curve, which could cause slope slide particularly at the inflection point of the slope deformation displacement curve and convex point of the corresponding velocity curve. The research results can provide a scientific basis and reference for slope stability monitoring and failure mechanism of similar mines.
Abstract: Coal strongly adsorbs methane and during the adsorption process there is always a thermal effect that leads to some changes in the coal structure and temperature. These changes have an electrical effect, such as a change in coal resistivity. The investigation of the thermoelectric effect of the adsorption process of coal has long been a hot research issue to industry experts and scholars. It is important that this thermoelectric effect be well understand with respect to the energy transfer and translation in the adsorption process, as well as to support geophysical electrical prospecting and disaster prediction. Both domestic and international scholars have conducted many studies on this issue. The heating and electrical effects in the process of coal adsorption are interrelated. Previous research has primarily addressed the single characteristic of gas adsorption or its application, with little attention being paid to their correlation. Most studies have used adsorption quantity to reflect the coal adsorption ability, and few have focused on the thermoelectric effect to study coal adsorption. Studies regarding coal particle size and the thermoelectric effect are even rarer. In this study, we investigated the temperature change and the current vs. time curves of three different metamorphic grade briquette coals, which consist of five different coal particle sizes, at a temperature of 25℃ and pressure of 3 MPa in the coal gas adsorption process. To do so, we used a SH-X multi-channel temperature tester and CHI660E electrochemical workstation. To determine the adsorption ability of coal with respect to the thermoelectric effect, we used the Clausius-Lapeyron equation to analyze the thermoelectric effect mechanism of coal and its correlation in the coal gas adsorption process of different particle sizes. The results show that an obvious thermoelectric effect accompanies the coal gas adsorption process. The temperature of the coal increases from 0.93℃ to 8.74℃ and the resistivity of the coal decreases 0.14-0.16 times from that of its stability when it reaches adsorption equilibrium. We found the temperature of the coal to increase as the particle size decreased and the gas adsorption quantity increased, but the coal resistivity change was the opposite. Coal temperature and resistivity change are strongly correlated with the gas adsorption quantity, with the correlation coefficients rd and rw ranging between 0.9502-0.9899 and -0.9316 to -0.9916, respectively, which are close to±1. Therefore, the heat adsorption process can reflect the adsorption ability of coal. When reaching equilibrium, the greater the temperature change, the higher the temperature and the lower the resistivity, which means that the adsorption capacity is greater, and in contrast, the adsorption capacity is weaker.
Abstract: Landslides are serious geological hazards along long-distance oil and gas pipelines. Especially common are discontinuous-developing single landslides. A single landslide hazard can cause anything from pipeline rupture and fracture to complete failure and shutdown, thus triggering serious secondary disasters. Risk assessments of oil-and-gas-pipeline landslides are an effective method for ascertaining the degree of landslide risk and can provide an important scientific basis for planning and decision-making regarding landslide prevention and control along long-distance oil and gas pipelines. In addition, risk assessments represent an important step in the pipeline-integrity management process. The evaluation system consists of both quantitative and qualitative indexes, which are characterized by randomness and fuzziness. To address the subjectivity and incompleteness of qualitative and semi-quantitative evaluation methods in the processing of randomness and fuzziness, the cloud theory was introduced, which can simultaneously reflect randomness and fuzziness. The golden section method was used to establish a five-level standard cloud metric for pipeline landslide risk and index weighting. In the cloud transformation process, this paper proposes uncertainty reasoning for the quantitative index and a floating cloud preference algorithm for expert group language as a qualitative index, which comprises the assessment model for landslide risk of oil and gas pipelines. The comprehensive evaluation results indicate that the floating cloud preference algorithm for the qualitative index is more suitable for the language of expert group decision-making than the synthetic cloud algorithm commonly used. In addition, the results of the four pipeline-landslide-risk evaluations are basically consistent with the results of the semi-quantitative method, which is consistent with the actual situation. This method softens the hard divisions between the inner boundaries of the index and simplifies the preprocessing of index data. It fuses the qualitative and quantitative evaluation aspects using composite decision-making and improves the accuracy, rationality, and visualization of the results.
Abstract: Red mud is the solid waste residue of bauxite ore digestion with caustic soda for alumina (Al2O3) production. China is currently the biggest producer of alumina worldwide. However, the comprehensive utilization rate of red mud is very low. Moreover, coal gangue is also a complex industrial solid waste, which is one of the largest in China. In this study, red mud, coal gangue, fly ash, and other industrial solid wastes were used to prepare a road base material in a laboratory to solve the environmental issues caused by these solid wastes. The mechanical and environmental properties and durability of Bayer red mud-coal gangue-based road base materials were investigated. Accordingly, 20 drying and wetting cycles and five freezing and thawing cycles were used to study the durability of the road base material. An inductive coupled plasma emission spectrometer was adopted to analyze the leaching properties of the road base material, while scanning electron microscopy-energy-dispersive X-ray spectroscopy techniques were used to investigate its element distribution. The results show that the unconfined compressive strength of the road base material, which cures for 7 days, is over 6 MPa and meets the strength requirement of the Chinese national standard when 75% red mud-coal gangue and 97% total solid wastes are added to the road base material. The strength of the road base material reaches 5.98 MPa after 20 drying and wetting cycles, thereby meeting the Chinese national standard. The strength still reaches 6.89 MPa after five freezing and thawing cycles. The leaching results indicate that the Na+ content in leachate is much lower than that required by the Chinese national standard for drinking water quality. Meanwhile, the radioactivity results of the pure red mud used herein meet the Chinese national standard for outdoor building materials. The energy spectrum and the mechanism of the alkali fixation results show that the silicon aluminum system could be more effective in consolidating Na+. The silicon and aluminum contents in the red mud-coal gangue-based road base material are relatively high, explaining the better Na+ consolidation. The results show good environmental and social benefits that can provide more options for road base materials.
Abstract: With the depletion of high-quality ore resources at home and abroad, the supply of domestic coking coal resources has become increasingly tense, and research on the non-blast furnace ironmaking technology has become even more necessary. The fluidized ironmaking technology can directly utilize powder ore, does not need to consume coke, and has good prospects for development. However, the sticking problem limits the fluidized ironmaking technology. Therefore, the sticking mechanism of particles must be explored, and inhibition measures must be put forward. Although many researchers at home and abroad have performed numerous studies on the influencing factors and inhibiting technologies of the sticking problem, the quantitative characterization and analysis of the sticking degree have rarely been studied. Similar to the fluid viscosity, the apparent viscosity of solid particles was introduced herein to characterize the interaction force between particles. The apparent viscosity of Fe2O3 particles with nano-SiO2 were measured by a rotational viscometer based on the principle of energy dissipation. The results indicate that the apparent viscosity of Fe2O3 particles increases with the increasing temperature and significantly decreases when nano-SiO2 is added. This result could be explained by the nanoSiO 2 coating on the particles inhibiting the agglomeration and sintering among particles. Sticking occurred during the fluidization process. The reduction of Fe2O3 particles was investigated by a micro-fluidized bed to verify the effect of nano-SiO2 on the apparent viscosity of Fe2O3 particles. Consequently, the results show that adding nano-SiO2 to the Fe2O3 particles can effectively improve the metallization rate and prolong the sticking time in the reduction process. Furthermore, the scanning electron microscopy analysis exhibits that the nano-SiO 2 coating on Fe2O3 particles reduces the diffusion activity of the iron atoms, blocks the contact between fresh iron, and inhibits the sintering of fresh iron, thereby making it difficult to form sticking points. In conclusion, adding nano-SiO2 to Fe2O3 particles can effectively inhibit sticking in the reduction process of the fluidized bed.
Abstract: The gas-liquid two-phase flow in the up leg of the Ruhrstahl-Hereaeus (RH) unit is one of the main momentum sources of the whole device, and it affects the flow state of the molten steel in the ladle. A physical model of 300 t RH in 1:6 ratio was set up to simulate the bubble behavior process and to measure the change of the RH circulation flow in the up leg and in the vacuum chamber. The gas-liquid fraction and the movement velocity of bubbles were measured to assess the residence time of the bubbles in the vacuum chamber. In addition, the formation of the bubbles at different values of the RH circulation flow and liquid-level height in the vacuum chamber were recorded by a high-speed camera. One of the main factors influencing the bubble formation is the increase of the lifting gas flow in the vacuum chamber. With the increase of blowing gas, the large independent bubbles undergo multiple collisions, break into small bubbles, and finally small and large irregular-sized bubbles coexist. When the liquid height is>80 mm, the residence time of the bubbles in the vacuum chamber achieves a stable value and cannot be further affected by the increase of the liquid-level height in the vacuum chamber. At a lifting gas flow of 3000 L·min-1, a weak decreasing trend of the residence time of bubbles is observed, and the bubbles start polymerizing in the vacuum chamber. In conclusion, for the 300 t RH physical model, the liquid height in the vacuum chamber is recommended to be 80 mm, whereas the lifting gas flow should be set at 3500 L·min-1. After these optimization steps, the decarburization time decreases from 21.4 to 17.5 min.
Abstract: The initiation and growth of fatigue cracks usually lead to serious fatigue failure of steel structures such as pressure vessels and pipelines. Therefore, for the safety and reliability of engineering structures, monitoring the fatigue crack growth and evaluating the severity of fatigue damage are important. An investigation of fatigue damage evaluation of 316LN stainless steel was presented by using the in situ acoustic emission (AE) monitoring technique. Fatigue crack propagation tests of 316LN stainless steel were carried out. The direct-current potential-drop method was used to measure fatigue crack propagation. At the same time, the AE technique was used to monitor propagation of the fatigue cracks in real time. The fatigue damage of 316LN stainless steel was qualitatively assessed by AE multi-parametric analyses such as the AE count, energy, and amplitude. Moreover, the quantitative relationships among AE parameters and the linear elastic fracture mechanics parameters were established for predicting the remaining fatigue life. The results show that the AE technique is effective for evaluating the severity of fatigue damage of 316LN stainless steel. The transition point on the curves of cumulated count, energy, and amplitude indicates that the fatigue crack propagates into the rapid crack propagation stage. This obvious change in AE could potentially provide failure warnings for researchers or engineers. Furthermore, the analyses of waveform and frequency show that the noise signal with low amplitude and long duration contains complex frequency components, whereas the crack propagation signal is a type of burst signal and the frequency is mainly distributed in the range from 80 to 170 kHz. In addition, the quantitative relations between fatigue crack propagation rate and AE rates such as the count rate, energy rate, and the amplitude rate were found to be linear, and these relations were used to predict fatigue crack length. The predicted fatigue crack lengths showed good agreement with the measured crack lengths. The results of the present investigation will be helpful for providing fatigue failure warnings and predicting the remaining fatigue life of engineering structures.
Abstract: Hot-rolled bimetallic composite plates are widely used because of their excellent properties. In the recent years, the enhancement of the combined performance of hot-rolled bimetallic composite plates has gained the attention of the industry. The molecular dynamics simulations were employed to assess the high-temperature combined performance of 316L/Q345R bimetallic plate systematically. The hot-compression process of the 316L/Q345R system was simulated on its atom structure model. The potential functions of the embedded-atom method were employed to describe the interaction between Fe, Cr, and Ni. The effects of temperature and compressive strain rate on the mechanism of the hot-compression deformation and the thickness of the diffusion layer were analyzed. The influence of adding a metal layer on the interface bonding performance was also discussed. The results show that increasing the temperature up to the composite melting point leads to the formation of a thicker diffusion layer at the bimetallic interface. However, an increase in the strain rate reduces the thickness of the diffusion layer, because the diffusion and compression time of the atoms shortens as the strain rate increases. The influence of the addition of a Ni or a Cr layer on the combined performance was investigated. The thickness of the diffusion layer of the bimetallic interface was increased by 134.5% when a lattice thickness Ni layer was added in the bimetallic interface; however, the addition of a Cr layer did not improve the combined performance. This study provides new insight into the factors that directly influence the performance of hot-rolled bimetallic composite plates.
Abstract: A static test and fatigue test of dissimilar single-lap self-piercing riveted joints were conducted for pure titanium (TA1) and aluminum-lithium alloy (AL1420). The fatigue performance of the joints was analyzed on the basis of the S-N curves; specifically, a fitting method was used to construct the S-N curves of the joints using three empirical parameters. Scanning electron microscopy was used to study the fatigue fracture surfaces of the joints and the microfatigue failure mechanism of the joints. The results indicate that the static performance and fatigue characteristics of the joints are inconsistent:the TA1-AL1420(TA) joint exhibits better static performance, whereas its fatigue characteristics are worse than those of the AL1420-TA1(AT) joint. The fatigue failure mode of the TA joint for the lower sheet is fracture; the fatigue crack appears in the sheet area around the rivet tail and extends along the width of the sheet, leading to complete fracture of the lower sheet. The loss of efficacy of the AT joint in the short-life region is related to fracture failure of the rivet, which exhibits brittle fatigue fracture. A mixed failure mode of rivet fracture and lower sheet fracture occurs in the middle-long life region, and a fatigue crack appears from one side of the lower sheet, extends along the width of the sheet to the other direction, and eventually lead to the failure of the lower sheet.
Abstract: In recent years, due to the increasing demand for lightweight products in automotive industries to save energy and decrease CO2 gas emissions, many aluminum alloy materials are being used in cars. Due to its good baking performance, 6016 aluminum alloy is popular. However, traditional forming technology cannot produce complex parts. Furthermore, recent studies have focused on the hot stamping of aluminum alloy sheets and, in particular, of 6016 aluminum alloy sheets. It is well-known that sheet-metal formability is enhanced when the blanks are formed in hot temperatures. When this is done, the forming limit curve will rise. The forming limit of the material during the hot forming process is an important index and studying the forming limit of aluminum alloys at high temperature is of direct significance to production practices. In this paper, the forming limit curve of 6016 aluminum alloy was studied by theoretical prediction and experimentation. First, to evaluate the flow stress of a 6016 aluminum alloy sheet, the uniaxial hot tensile tests were conducted over a strain rate range of 0.01-1 s 1 and a temperature range of 400-500℃. Then, the Fields-Bachofen constitutive equation was established with considering strain hardening and strain rate enhancement, which matched well with the experimental measurements. Then this constitutive equation was introduced into the forming limit theory. Finally, based on the M-K groove theory, the forming limit curve of 6016 aluminum alloy was theoretically predicted, and the prediction results were validated by using the Nakazima test method. The comparison of the experimental and predicted values shows that the M-K groove theory is reasonable and accurate in predicting the forming limit curve. The effect of the initial inhomogeneity factor was analyzed on the forming limit curve. The results show that the prediction curve moves in the positive direction of the vertical coordinate, with an increase in the initial inhomogeneity factor. Also, the effect of the initial inhomogeneity factor on different strain paths differs, and the impact on the tension-tension strain states is greater than that on the tension-compression strain states.
Abstract: A theoretical model of a vibrating electret electrostatic energy harvester for a double-ended fixed beam was established herein for a low-frequency vibration energy in the environment. The key parameters of the electrostatic energy harvester were optimized by a MATLAB/Simulink numerical analysis. The relationship between the output power, resonant frequency, and half-power bandwidth and the electret surface potential, air gap, and load resistance was also studied. The magnitude of the external excitation acceleration and the size of the electret remained constant. The numerical results are as follows:(1) the existence of an optimal surface potential makes the output power of the electrostatic energy harvester reach the maximum value. The soft spring effect gradually increases with the increase of the surface potential, making the resonant frequency of the energy harvester device shift. The bandwidth also gradually increases. (2) An optimal initial air gap maximizes the power when the surface potential is constant. The half-power bandwidth decreases as the gap increases. (3) An optimal load maximizes the power when the surface potential and the air gap remains constant. The resonant frequency is offset as the load decreases. (4) An optimal load is used to maximize the half-power bandwidth when the air gap is constant. The larger the surface potential, the greater the half-power bandwidth under the same load. Experiments show that the output characteristics of the energy harvester under different load resistances have the following characteristics:with the increase of the load resistance, the output power and the half-power bandwidth increase at the beginning, then decrease. The maximum output power is 0.188 mW when the load resistance is 90 MΩ. In addition, the half-power bandwidth reaches the maximum value of 4.7 Hz when the load resistance is 330 MΩ.
Abstract: Herein, a robust guaranteed cost control weighting matrix optimization method based on chaos artificial fish swarm algorithm was proposed to overcome the dependence on the experience of selecting a weighting matrix in order to achieve robust guaranteed cost control and to overcome the inability of the current method to minimize the system conservative. The objective of this methodology is to estimate the optimal weighting matrix by considering the robust guaranteed cost control boundary as an objective function for optimization. The improved artificial fish swarm algorithm combines the chaos search and the artificial fish swarm algorithm with adaptive step and vision, which effectively resolves various drawbacks, including low convergence rate during the latter stage and easiness of being trapped in a local optimal solution, of a basic artificial fish swarm algorithm. The superiority of the improved artificial fish swarm algorithm proposed herein was verified by the contrast results of the test function. Furthermore, the effectiveness of the weighting matrix optimization method was validated using some application examples.
Abstract: When stereoscopic videos are transmitted on the no-quality-assurance internet, frame delay occurs in the left and right views, which affect the stereoscopic sensation as well as the viewing quality. In this paper, the stimulus of motion-in-depth and motionin-lateral asynchronous stereoscopic videos were analyzed and they were compared via qualitative and quantitative assessments. In this quantitative experiments, the well-known electroencephalogram (EEG) was utilized. A total of ten subjects was recruited to participate in an experiment, in which they watched randomly presented asynchronous stereoscopic video clips. For the qualitative assessment, after viewing one clip, the subjects were asked whether they perceived any asynchronicity in the frames. The degrees of asynchronicity included no delay, one frame delay, two frame delay, and three frame delay. The electroencephalogram (EEG) signal of each subject was recorded as they viewed the clip. Next, the event-related potentials (ERPs) were extracted from the EEG signals and the behavioral data and the ERPs were analyzed to compare the different reactions to the depths and lateral extents of the asynchronous stereoscopic motion. The results reveal that the maximum allowable asynchronicity perceived for motion-in-depth stereoscopic video clips is one frame, whereas there must be no delay in the motion-in-lateral stereoscopic video clips. In addition, compared with being stimulated by the motion-in-lateral asynchronous stereoscopic video clips, a magnitude of P300 has a wider range when the subjects are stimulated by motion-in-depth asynchronous stereoscopic video clips. This indicates that the brain becomes more active in this circumstance. At the same time, the latency of P300 is longer than when stimulated by the motion-in-lateral asynchronous stereoscopic video clips, which means that when the subjects are stimulated by the same degree of asynchronicity of motion-in-depth and -in-lateral stereoscopic video clips, more time is required to process the stimulation of motion-in-depth stereoscopic video clips.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
