查看更多>>摘要：? 2022 Elsevier LtdA computational model for the determination of the fatigue life of sintered gears is presented in this study. The total fatigue life of sintered gear, N, is divided into the crack initiation life, Ni, and crack propagation life, Np. The number of cycles for crack initiation in a gear tooth root, Ni, is determined by using the strain-life approach and the low-cycle fatigue parameters of the sintered gear material available in the literature. The number of cycles for crack propagation, Np, to a critical length is obtained by using the simple Paris law and the material parameters taken from the authors’ previous work. The comprehensive computational analyses in the framework of the Ansys-software were performed to obtain the strain-stress field in a gear tooth root, and to determine the stress intensity factor at the crack tip. The numerical results were compared with the experimental data available in the literature.
查看更多>>摘要：? 2022 Elsevier LtdThe poor reliability of shearer restricts the development and production efficiency of thin coal seam. The dynamic characteristics of the key parts have a great influence on the reliability and fatigue life of the thin seam shearer. In order to achieve high-yield and high-efficiency production of thin coal seams, the instantaneous load on the spiral drum was calculated based on the mechanical model of the spiral drum during the cutting process and the coal sample properties. According to the structure of the shearer and the material of key parts, a rigid-flexible coupling model of the shearer was established, and the stress information of the rocker arm shell, planetary carrier and planetary shaft was obtained by dynamic simulations. The membership function between material stress and structural reliability was constructed by Gaussian membership function, the main factors affecting the reliability of shearer were analyzed by orthogonal simulation test and PSO-BP neural network. The fatigue life of rocker arm shell, planetary carrier and planetary shaft were predicted by counting the rain flow of the stress information. Measures to improve the reliability and fatigue life of the shearer were proposed based on the analysis results, and effectiveness of the method proposed in this paper was verified by the practical application.
查看更多>>摘要：? 2022 Elsevier LtdIn tandem cold-rolling production, sheet fractures are interrelated to both conveyance stress and transverse cracks during conveyance process. The residual tension or sheet contour cannot completely explain the early fracture problem. It is found that small lateral crack reduces fracture threshold of sheets destructively during cold rolling and coiling processes without rolling stress. Several lateral notches were machined on cold-rolled intermediates of silicon steel to simulate edge cracks in rolling processes. Based on tensile test and laser confocal microscope, the damages of lateral notches on tension resistance of sheets were investigated. Then, the shape effect and size effect of lateral notches were analyzed. The notch depth could negatively affect energy absorption capacity of sheets before tensile fracture. Meanwhile, the sharp notch could deteriorate elongation ability of sheets before necking. Both factors reduced fracture threshold of sheets and tensile redundancy and conveyance stably capacity of tandem rolling mills, promoting sheet fracture.
查看更多>>摘要：? 2022 Elsevier LtdAnalysis of slope stability has been a challenge for researchers and engineers since the 17th century with Hooke. This paper used geometric, kinematic and seismic methods to analyse the stability of selected slopes cut into the gneiss of important roads connecting Central Africa countries, subjected to particle and block falls. The selected slopes were also studied to verify the factor on which engineers base their design. The results show that the angles are sharp and that the selected slopes are unstable, made in gneiss with a diptic state and a particle acceleration of 1.57 km/s2, confirming that the slopes are sensitive to falling particles. This study also shows that, in a moderately active seismic zone in Central Africa, slopes cut into fractured gneiss are generally unstable and engineers must also consider FS. To make these slopes more stable, they can be plastered, trenched or cut at angles <10°.
查看更多>>摘要：? 2022 Elsevier LtdFlat plate-column joints with in-plane constraints exhibit a suspension mechanism under large deformations after punching shear failure, which significantly affects the progressive collapse behavior of the entire flat plate structural systems. However, in-plane constraints were ignored in the existing tests by which the suspension mechanism could not be exhibited and consequently the post-punching resistance was significantly underestimated. To fill this gap, a static pushdown test was conducted on eight flat plate-column joints with in-plane constraints until their post-punching resistances being completely lost. The influences of the punching directions and the structural parameters including slab thickness, reinforcement amounts and arrangement of flexural reinforcement on the post-punching failure mechanism were analyzed. An analytical method for calculating the post-punching strength was proposed and validated by the test results. The contributions of each layer of reinforcement to the post-punching resistance were also quantified.
查看更多>>摘要：? 2022 Elsevier LtdThe main reason of gob-side entry deformation is surrounding rock movement near the goaf. During underground excavation, it is common that surrounding rock behavior and crack development under unstable overlying strata are substantially different from rock under strong and competent main roof. To study the failure mechanism due to main roof deformation near the edge of goaf, UDEC Trigon model was constructed with strong and thick hanging roof. Laboratory and Rock Quality Designation (RQD) results were used for model calibration. Results show that stress acting on the pillar increased dramatically due to roof subsidence prior to roof caving and breakdown. At the same time, considerable number of fracture developed in the roof and rib. After separation of failed roof, the influence on crack development decreased. Once the separated roof was stabilized, failure zone of surrounding rock stopped expanding. To manage the unsymmetrical deformation due to dynamic loading from hard main roof under gob-side entry driving, a combined strata control method was proposed, including roadway expansion, long cable bolt installation and roof cutting via blasting. Field trials prove that the optimized supporting plan can effectively control the large deformation of 9102 gateroad; and, the implementation of roof cutting can reduce gateroad failure from dynamic loading.
查看更多>>摘要：? 2022During the excavation process of hard rock tunnel by tunnel boring machine, rock breakage is mainly realized by the disc cutter, of which the cutter ring is in direct contact with the rock and therefore is prone to failures like wear, distortion and fracture. In this paper, in order to prevent the frequently-occurred failure of the cutter rings made of H13 medium-alloy steels, the properties of the specimens that were made of 42CrMo low-alloy steel and had undergone different heat treatment processes were investigated, including chemical composition, impact absorbed energy, hardness and wear resistance. The results pointed out that the combination of quenching at 850 °C and tempering at 180 °C and 230 °C was the optimum process, through which increased impact absorbed energy, equivalent hardness and wear amount was achieved in comparison with that of the H13 specimen. Achievement of this paper will facilitate both failure prevention and cost reduction for the disc cutter of tunnel boring machine.
查看更多>>摘要：? 2022 Elsevier LtdTo improve the dynamic reliability analyses of complex structures, intelligent weighted Kriging-based moving extremum framework (IWKMEF) is developed by absorbing moving least squares (MLS) thought, Gaussian weight, particle swarm optimization (PSO) method and Kriging model into extremum response surface method (ERSM). ERSM method is employed to convert the dynamic output response into extremum values. MLS thought is used to find effective samples. Gaussian weight is to improve modeling precision. PSO method is applied to optimize the local compact support region radius of MLS. The radial deformation of turbine blisk is conducted to verify the effectiveness of IWKMEF method. The results show that the reliability degree of turbine blisk is 0.9984 when the allowable value is 1.9217 × 10?3 m; The developed IWKMEF holds high performance by comparing direct simulation, ERSM and traditional Kriging model. The efforts of this study provide a useful insight for the dynamic reliability analysis of complex structure.
查看更多>>摘要：? 2022 Elsevier LtdPhysical salt attack (PSA) is a key damage mechanism of concrete in salt-bearing environments. Multiple case studies were reported throughout literature on PSA of concrete; yet, without any case on the performance of repaired concrete elements. The current paper presents a case study analyzing the condition of repaired concrete piles in 47-year-old administrative building in Winnipeg, MB, Canada, after 22 years from repair works. Deterioration of the concrete piles was visually observed above the ground level and repair zones, in the form of scaling, crumbling and reduction of cross section. In addition to fluid transport and pore structural features tests, mineralogical, thermal and microscopy analyses were performed on concrete chunks/cores extracted from the piles to elucidate the underlying mechanisms of damage. The repair concrete was capable of mitigating chemical and physical sulfate attacks; however, it could not stop the progress of PSA on the concrete above it, urging for careful design of repair strategies for elements subjected to PSA. Recommendations for future repair in this case are also presented.
查看更多>>摘要：? 2022 Elsevier LtdSeepage control is one of the key issues for the design and construction of deep soil excavation projects. A seepage failure occurred around an abandoned pile in a foundation pit with confined aquifer layers, and caused damages to the retaining wall and support system and surrounding environment. The causes of the accident are analyzed, and the reconstruction of the project are introduced. The seepage failure was attributed to the defects in the three-axis mixing piles and the potential weak region created around the abandoned pile. It was finally controlled by filling the whole foundation pit with water. A systematic reinforcement of the foundation pit was carried out. The soil disturbed by the seepage failure was reinforced by two-shot process grouting and sleeve valve pipe grouting. The cast-in-place piles and prestressed assembled steel struts were constructed to strengthen the original retaining wall and support system. An ultra-deep (61.5 m) trench-cutting re-mixing deep wall (TRD) was successfully constructed in complex stratum, and showed good waterproof performance through a pumping test. After the formal dewatering inside the foundation pit by three stages, the project was successfully finished. This study could provide a wealth of experience and guidance for the design and construction of future similar deep excavation projects.
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