查看更多>>摘要：? 2022 Elsevier LtdThe high reliability of the longwall shearer is far-reaching to the efficient operation of coal mines and the stable supply of energy. However, traction problems caused by the haulage wheel's failure are prominent. Therefore, for exploring the damage mechanisms of the haulage wheel by the shearer's pose and optimizing the traction structure, a meshing model between haulage wheels and pin row is established, with the non-standard center distance and the oblique angle, respectively. And the effects of the shearer's pose of the jumping and swinging around the vertical direction on meshing performances are studied. The result indicates the radial runout of haulage wheels is the most violent when the teeth alternate meshing, and the maximum runout amplitude is 1.563 mm. With the radial runout increasing, the average peak force increases, and the stress concentration range of the tooth root expands to the pitch line position. The shearer's swing around the vertical direction causes the axial impact force of the haulage wheel. With the swing angle increasing, the stability and safety of the haulage wheel decrease. As the velocity increases, the axial slip on the tooth surface aggravates while effective meshing width decreases when the haulage wheel is affected by oblique angle. The result provides a reference for reducing the shearer's hauling fault.
Noraphaiphipaksa N.Kanchanomai C.Borrisutthekul R.
12页
查看更多>>摘要：? 2022 Elsevier LtdAmong various health care demands for ageing population, the total knee arthroplasty (TKA) is currently one of the major health care expenses. TKA is a process to replace the surfaces of femur and tibia with the knee prosthesis, i.e., femoral component, tibial tray, and spacer. During service, the metal tibial tray is under cyclic bending; thus, the fatigue failure is possible. The cyclic bending and fatigue failure of tibial tray can be enhanced by the malalignment of knee prosthesis due to the change of bodily structure in ageing population. To investigate the influence of malaligned knee prosthesis on fatigue life, the numerical stress analysis and in-vitro fatigue test of tibial tray based on ASTM F1800 were performed. For tibial trays with malalignments, the location of the maximum stress range was near the junction between stem and tray, which corresponded to the location of fractures observed previously in clinical application.
查看更多>>摘要：? 2022 Elsevier LtdThe rock cutting performance and cutter-rock contact behavior of partial-worn cutters are investigated via scaled rock cutting experiments. The results reveal that the partial-wear of the cutter reduces the normal force, while the tangential force increases. Changes are also observed in the rock breaking mechanism. Although the rock breaking capacity of the partial-worn cutters is not significantly reduced, the increase of volume ratio of the rock powder results in a rise in specific energy, indicating that the energy utilization of the partial-worn cutters is relatively low. In addition, plastic deformation and abrasive wear are observed on the partial-worn cutter surface. The changes of motion modes and surface geometry play a key role in the above-mentioned phenomena.
查看更多>>摘要：? 2022 Elsevier LtdTo consider the multiple interactions between offshore sites and sea-crossing bridges under seismic actions, a seabed–pile–seawater–bridge interaction model is established by the ADINA software [1]. This study uses seismic fluctuation analysis as an input to bedrock ground motion. It reflects the influence of submarine sites and seawater layers on ground motion characteristics through the fluid-solid coupling of seawater to the seabed. It was found that the whole bridge piers considering the coupling effect are in an elastic state. The yielding of the isolated bearings occurs. Also, the seismic response of the bridge structure under the seabed-pile-seawater-bridge interaction is significantly higher than those under the direct input of the ground motions from the fixed basement assumption. In addition, when the pile cap is above the seabed, the average seismic response of the bridge structure is 1.2–1.3 times the response when the pile cap is below the seabed. Therefore, the seismic design of marine structures should take full account of the influence of the submarine site and the seawater layer. Otherwise, it will result in greater seismic risks for marine structures such as sea-crossing bridges. In addition, this study also suggests the influence of the pile cap location on the seismic response of the bridge.
查看更多>>摘要：? 2022The deformation and failure of deep soft rock roadways become more prominent. In this paper, two true triaxial model tests were carried out to investigate the deformation and failure law of deep soft rock roadway excavation and the stability characteristics of the surrounding rock after the support. The surrounding rock stress and roadway deformation characteristics can be divided into three stages: advance influence, rapid change and stability. The deformation and failure sequence during the excavation process of the model roadway is “vault → sidewalls → arch springing → roof collapse”. Roof stability is the top priority. After the supporting structure is applied, the surrounding rock stress increases obviously and the roadway deformation decreases. The model test results are verified through field monitoring, and the key deformation parts of the deep soft rock roadway and the characteristics of the supporting structure force are clarified, which can provide reference for later research.
查看更多>>摘要：? 2022 Elsevier LtdWidespread en-echelon fractures may induce some disasters such as landslides of rock slopes and destabilization of underground excavations. Bolt support has been widely used in various rock engineerings for many years, but the bolting behavior of en-echelon fractures has rarely been studied. In this study, the anchorage effect of conventional rigid bolt and energy-absorbing bolt was investigated by direct shear tests under constant normal stiffness conditions. The bolting performance of the two bolts was quantitatively evaluated based on shear strength and dilation indices. The test results show that the anchorage effect of bolt is closely related to the bolt material and fracture angle. This is essentially determined by the deformation mechanism of bolt in different shear failure structures. A bolt deformation factor was proposed to predict the breakage displacement of bolt at different fracture angles and a bolt contribution index was defined to comprehensively evaluate the bolting performance.
查看更多>>摘要：? 2022 Elsevier LtdCracking failure of Incoloy 800H welded joints used for about eight months occurred in hydrogen reformer outlet pigtail tubes. Visual inspection, microscopic examination, chemical composition and microhardness testing were performed to find out the failure mechanism. The results indicated that microcracks were discovered in the fusion zone and heat affected zone (HAZ). The crack propagation mode was intergranular and irregular. The cracked regions were occupied with some oxides in the fusion zone. The Cr content at the grain boundaries was abnormal and intergranular oxidation was found in the HAZ. The microcracks in the outlet pigtail tubes were caused by stress relaxation, and oxidation at grain boundaries. The intergranular oxidation caused the embrittlement at the grain boundaries during long-term service. From the investigations, it was believed that the failure of welded joints in the outlet pigtail tubes originated from stress relaxation cracking during high temperature service.
查看更多>>摘要：? 2022 Elsevier LtdFiber reinforced polymer (FRP) composites are being extensively considered for construction of ships and marine structures. Due to harsh environmental operational conditions, failure prediction of such structures is an imperative in this industry sector. This paper presents the final results of a 2-year research of real marine environment induced changes of mechanical properties in FRP composites. Realistic environmental input parameters for structural modeling of marine structures are crucial and can be obtained by conducting tests in real sea environment for prolonged periods, as opposed to usual accelerated laboratory experiments. In this research, samples of epoxy/glass and polyester/glass with various fiber layout configurations have been submerged under the sea for periods of 6, 12 and 24 months. An analysis of mass changes, marine microbiology growth, tensile strength and morphological structures of the coupons was performed and compared with samples exposed to room environment. All samples exhibited an increase in mass due to seawater absorption and microorganism growth in the organic resins (matrix). The tensile strength loss variation through the periods of submersion showed a correlation with the fiber layout configuration. The results of optical and scanning electron microscopical investigation indicated significant matrix morphological changes primarily due to salt crystal formation and the impact of sea microorganisms embedding in and attaching to the resin. The outcome of this research will be the basis for a set of realistic input parameters for a failure analysis numerical tool currently in development that can be applied for life-time behavior predictions of marine structures.
查看更多>>摘要：? 2022 Elsevier LtdThis study is aimed to analyse fatigue life of orthopedic plates due to cracks initiated in the stress concentration areas. Material used for this analysis was typical orthopedic alloy, Ti-6Al-4V, strong but not very ductile, meaning also sensivite to cracking, as indicated by its mechanical properties, such as tensile strength, impact toughness and fracture toughness, as well as by high fatigue crack rate, all of them tested and analysed here. Extended finite element method (XFEM) in ANSYS software was used for simulating the fatigue crack growth in 5 orthopedic plates with different geometries. Results for crack length and stress intensity factor vs. number of cycles are given, indicating plate D as the best option regarding residual life. Crack paths are analysed in all 5 plates to explain such a behaviour, indicating benefits of initial crack growth into length, followed by growth into depth. Also, the effect of geometry of plates is considered to explain differences in life predictions for 5 different plates.
查看更多>>摘要：? 2022 Elsevier LtdThe article analyzes the effects of a fire that occurred in a small room of an electrical switchboard in the underground garage of a multi-storey residential building. The building was in the final stage of construction, but many of the ‘passages’ of the installation through the walls and ceilings were not yet fire-protected, ie., the fire integrity requirement was not met. It results that a spread of fire was much larger than could be expected. The research carried out in order to assess the condition of the structure after the fire were presented, in particular the selection of members that: (1) had to be dismantled, (2) required significant strengthening or repair, (3) could be used after only minor cleaning works. Due to the short time to carry out the assessment, it was mainly based on non-destructive tests (NDT) results. The conclusions from the conducted assessment and analyzes were presented. A small and seemingly easy to control fire, which started in the underground garage, spread up to 12 storeys above ground level. The fire was difficult to control due to incomplete works in the field of securing installation passages through the partitions. These works were to be carried out in the final stage of the construction of the building, while the electrical installation was already in use. Damage to reinforced concrete members had an unexpectedly large extent due to thermal spalling of the concrete. Significant intensification of this phenomenon was caused by the high moisture content in ‘relatively young concrete’ (short drying time from casting the members) and the close location of the burning electrical wires in relation to the structural members. The possibilities of estimating, but still sufficiently reliable, assessment of damage to members using NDT was pointed out.
NSTL
Elsevier