查看更多>>摘要：The present study aims to characterize the cracking behaviour of high-density poly-ethylene (HDPE) pipe elbow. Experimental studies were performed to determine the mechanical behaviour of HDPE and study the anisotropy of the material. Tension tests were performed on compact tension (CT) specimens to identify the toughness value, expressed by the critical value of the J-integral J_(IC). These tests were carried out on specimens cut from a PE100 plate with a different orientation angle with respect to the extrusion direction. The testing results have shown that HDPE can be considered as an isotropic material. The methods used to calculate the J_(IC) value resulted in different value. Due to these uncertainties, a study of a failure criteria using crack tip opening displacement (CTOD) was proposed and conducted. The combination of the J-integral and "CTOD" method gave the possibility to determine for the critical value of the J-integral as a value of the fracture toughness of the HDPE. The obtained results suggest that the value of 8.4 kJ/ m~2 can be considered as the J_(IC) fracture toughness required to initiate the crack for the HDPE.
查看更多>>摘要：Concrete median barriers on highways are typical road safety facility that requires predicting correctly the amount of fragments generated during a vehicle collision. The fragmented pieces from the median barrier can cause secondary accidents to a vehicle coming from the opposite lane. Therefore, predicting the amount of fragments depending on the impact severity is important to prevent any secondary accident. Many researchers have studied to predict the damaged area and strain of concrete. Such predictions of concrete structural behavior following impact loads mostly used FEM. However, FEM has a limitation in predicting the fragmentation amount since it simulates fragmentation through element deletion. As an alternative, Smooth Particle Hydrodynamics (SPH) can be used for predicting the amount of fragments or the motion of fragments since these are not affected by the mesh. In the present study, impact analysis was performed to predict the amount of concrete fragments due to vehicle collision. The obtained results of SPH analysis showed that the amount of fragments can change depending on different velocity-to-mass ratios at a fixed local impact energy. Using the results of the SPH analysis, multiple regression analysis (MRA) was conducted further. The MRA showed a rather low coefficient of determination (R2) compared with the SPH analysis results. Therefore, as a future study, with the expectation of improvement, a method such as ANN (Artificial Neural Network) that can predict the amount of fragments including uncertainty is necessary.
查看更多>>摘要：With the rapid development of underground space construction, there are more and more large-scale deep foundation pit projects on one side of the metro station. Unilateral deep excavation will result in an imbalance of the earth pressure on both sides of the existing metro station, which is a major engineering risk. Therefore, considering the station width and the excavation depth, this study focuses on the deformation characteristics and failure evolution process of the existing metro station structure caused by unilateral excavation based on the physical model test and discrete element method (DEM) analysis. This research shows that the lateral deformation of the top of the station caused by unilateral excavation is the most significant. Secondly, as the excavation depth increases and the station width decreases, the increase rate of the station overall inclination and lateral displacement becomes more significant. Thirdly, the structure fails when the excavation depth is 5/6H (H is the station height). Then the station instability leads to three disturbed regions in the adjacent stratum. The contact force between soil particles in the disturbed region is small and the stability is poor. Finally, the failure evolution process of the existing station under unilateral excavation is divided into three stages: (a) when the excavation depth is 0-1/2H, the soil and structure are stable; (b) when the excavation depth is 1/2-3/4H, the lateral deformation and inclination of the station reach the security warning range; (c) when the excavation depth is 3/4-1.0H, the structure is unstable and slips laterally, resulting in the ground collapse and local soil extrusion failure. This study reveals the risks of the existing station at different excavation stages, which can make risk prediction for the construction of the project.
Samuel Olukayode AkinwamideAndrew VenterOjo Jeremiah Akinribide
10页
查看更多>>摘要：The use of 2205 duplex stainless steel (2205 DSS) in the petrochemical and nuclear industries is fast replacing carbon steel and other convectional alloys due to its excellent corrosion resistance and improved mechanical properties it offers. The effect of residual stress on corrosion behaviour of hot and cold rolled 2205 DSS in a chloride environment is investigated. As received hot and cold rolled duplex stainless-steel samples were characterized using a scanning electron microscope (SEM) for microstructural phase analysis. Residual stresses of varying percentages (20, 40, and 60%) were applied to duplex stainless steel samples machined to micro tensile dimensions. The residual stress analysis of the necked region was analyzed using Bruker D8 Advance X-ray diffractometer, while potentiodynamic polarization was carried out in 3.5 wt% NaCl to access the corrosion integrity of the necked region. The center and average principal stress analysis (S11 and S22) of hot and cold-rolled stainless steel in the necked region showed the deformation of austenite and ferrite phases due to tensile pulling with more tensile stress in the austenite phase. SEM micrographs of corrosion substrates revealed the dominance of corrosion in the austenite phase within the necked region in hot rolled samples.
查看更多>>摘要：Aiming at the problem that the uneven deformation of the crossbeam of the new ground anchor counterfort grille dam under the impact of debris flow is easy to cause the overall damage of the structure, the crossbeam is simplified as a mechanics model of multi - span continuous beam supported on the grille columns, and the internal force calculation formulas of the crossbeam under the displacement and the local failure of the bearings are deduced. Combined with an example, during the process of bearings from the displacement to local failure, the internal force variation of the crossbeam are analyzed. The results show that when the single bearing is displaced, the mid - span bearing has the greatest impact on the internal force of the crossbeam. When the two bearings are displaced at the same time, the two side - span bearings have a greater influence on the internal force of the crossbeam. When three bearings are displaced at the same time, the influence on the internal force of the crossbeam is the smallest. When the single bearing fails, the failure of side - span bearing has the greatest influence on the internal force of the crossbeam, the mid - span bearing failure is second. Therefore, the reinforcement at each bearing of the crossbeam should be considered to meet the force requirements after the internal force redistribution in the design, so as to ensure the safety of the structure after the positive and negative bending moment of bearing are converted. In addition, when displacement or failure of bearings occur, attention should be paid to meet the limit requirements of structural deformation and stability. The research results can provide a theoretical basis for the reliability analysis of the new ground anchor counterfort grille dam.
查看更多>>摘要：To reveal the features of the gear wear and failure correlation on the system reliability, comprehensive consideration of PMSM characteristics, gear internal structure and load torque, the permanent magnet gear transmission system dynamic model is established based on the motor theory and Maxwell equation. The gear variable amplitude fatigue load spectrum is statistically analyzed by rain flow counting method and Goodman theory. On this basis of nonlinear damage theory and modified P-S-N curve, the dynamic reliability of gear single failure mode considering the number of random loads and strength degradation is predicted. Finally, based on the Copula function, the change regularities of the system dynamic reliability are analyzed by using the relationship between the correlation function and reliability.
查看更多>>摘要：In the past two decades, reports of the premature failure of cable bolts used in the mining and civil industries have been increasing. Previous studies have established that failure occurs through hydrogen-induced stress corrosion cracking (HISCC), which is a type of environmentally assisted hydrogen cracking. However, to date, the cause of HISCC has been unclear. For the first time, we studied the role of microorganisms in the failure of cable bolts using components present in SCC-affected mines. Stressed coupons were prepared from the cable bolt wires and tested in groundwater with additions of sulphate-reducing bacteria, coal, clay, pyrite and lactate. It was found that hydrogen sulphide (H_2S) produced by sulphate- and sulphur-reducing bacteria promoted hydrogen diffusion into the steel and, in the presence of stress, caused HISCC. This suggests that control of H_2S production should be a priority for mining and civil industries to avoid premature failure of anchoring systems.
查看更多>>摘要：In order to study the influence of wheel-rail random dynamic interaction on the fatigue damage for fastening clips, a three-dimensional (3-D) high-speed railway vehicle-track coupling random dynamics model is established based on the random theory of the probability density evolution method (PDEM). The number theoretic method (NTM) and stochastic harmonic functions (SHF) are employed to generate the representative random track irregularities. Furthermore, a refined finite element model of WJ-8 fastening system is established, and the stress time history results of the clips are obtained based on the co-simulation analysis. Eventually, the rain-flow counting is introduced to study the influence of random track irregularities on fatigue damage of fastening clips combined with cumulative damage theory and the S-N curve of the clips. The results show that, the dynamic characteristics and stochastic probability evolution mechanism of the vehicle-track random system considering random track irregularities, as well as the evolution characteristics of the fatigue failure probability of clips with service time are accurately reproduced based on PDEM. Significantly, the fatigue damage of fastening clips caused by one vehicle passing by follows the lognormal distribution with a mathematical expectation of 2.35 × 10~(-8) and a variance of 1.48 × 10~(-12). The 95% confidence interval of mathematical expectation is [7.05 × 10~9, 5.89 x 10~(-7)] and the 95% confidence interval of variance is [1.37 × 10~(-13), 1.59 × 10~(-11)]. Additionally, the longer the service time of the fastening system, the more serious the fatigue damage of the clips and the greater the fatigue failure probability.
查看更多>>摘要：A sliding accident occurred in the embankment slope of a highway in the south of China. The cause of the failure was investigated based on the geological data, construction conditions and numerical results. Measures were taken to reinforce the embankment including loading berm, steel pipe grouting and steel sheet pile. The applicability of the reinforcements and the stability of the reinforced embankment were analyzed through numerical simulation. A scheme for the time-dependent slurry diffusion was proposed. The grouting process was realized in the numerical model through extensive programming, and the diffusion range of the cement slurry with the duration of grouting can be monitored in the numerical model, whereby the effect of the grouting was evaluated. The paper not only can provide valuable hints for the research relating to the stability analysis of slopes, but also are instructive for the treatment of sliding accidents in the soft soil embankments in the area of heavy rainfall.
查看更多>>摘要：Fatigue cracks may occur at the weld toe or weld root in the fatigue control locations of the metro bogie frame, an effective fatigue assessment method is needed to analyze the bogie's fatigue reliability thoroughly. In this paper, the fatigue property tests of typical welded joints were completed, combined with the effective notch stress concentration factor, the effective notch stress S-N curve was determined. The effects of joint dimensions were studied to get a safer S-N curve which could be applied to the fatigue reliability analysis. This paper provides a theoretical and practical basis for the fatigue assessment of the metro bogie frame under service conditions.
NSTL
Elsevier