查看更多>>摘要：Wheelset geometric eccentricity and mass eccentricity are generally considered to be the main reasons behind the formation of the 1st order out-of-round (OOR) wear (or eccentric wear) of railway wheels. Based on finite element simulation, the relationship between wheelset geometric eccentricity and the high-order OOR wheels of high-speed trains was studied in this paper. Moreover, the reason for the phase difference between the polygonization on the left and right wheels of a railway wheelset was discussed. The results show that, when the train runs at a high speed of 237 km/h, a wheelset's geometric eccentric value greater than 0.7 mm can lead to longitudinal creep forces on the left and right wheels to periodically reach saturation during operation, causing frictional self-excited vibrations of about 605 Hz in the wheel-rail systems; and resulting in 24th ~ 25th order wheel polygonal wear. The phase difference between the geometric eccentric directions of the left and right wheels can cause the phase difference between the saturation states of the creep forces on these wheels, resulting in the phase difference between the 1st and 24th ~ 25th order OOR shapes on these wheels. In addition, during the assembly of the trailer wheelset, when the phase difference between the residual static unbalance values of the wheel and brake disc is 180°, the unbalanced force couple caused by the wheelset mass eccentricity is minimal, which then slows down the formation of 1st order OOR shapes on the trailer wheels.
查看更多>>摘要：The failure and design of coal pillars have always been the focus of research in the field of mining engineering, and there are often many water resources in goafs with rich aquifers. Under the influence of mining and long-term water invasion, it is easy to cause gradual failure and instability to coal pillars. Based on this, this paper proposes a numerical simulation method for the coupling of engineering scale mining-water invasion and a quantitative index of the damage ratio of coal pillars. The numerical parameters are calibrated with measurement data from coal-pillar stress. In the simulation process, the evolution of the strength, damage ratio, water pressure, stress, strain, and other parameters in coal pillars under the effect of mining-water invasion is realized, and the progressive failure mechanisms of coal pillars under mining-water immersion are revealed. On this basis, the effects of goaf water-level height and coal-pillar width on coal-pillar stability are quantitatively analyzed, and the critical goaf water-level height corresponding to different coal-pillar widths is obtained. Using the simulation results of this paper, the instability of a coal pillar in a coal mine is effectively solved, and the deformation of the coal-pillar rib and roof of the tailgate is reduced by 39.6% and 30.8%, respectively, which ensures the safe production of the longwall face.
查看更多>>摘要：Novel current-carrying contact pairs were designed in this study, consisting of an inner raceway, outer raceway, and elastic ring. The effect of rotation speed on the current-carrying tribological properties was investigated using a rolling tribometer. As the rotation speed increased from 240 r/min to 600 r/min, the total friction force in the steady-state period increased from 3.8 N to 7.6 N, and the contact resistance decreased from 0.52 Ω to 0.34 Ω. Scanning electron microscopy and optical microscopy revealed that high rotation speeds and the presence of a current promoted surface fatigue and the generation of cracks. The X-ray photoelectron spectroscopy results indicated that more nascent metals were exposed on the rolling surface at higher speeds, which is beneficial for the electric contact. Compared with previous rigid rolling pairs, the weight of the elastic ring was significantly reduced, and no arcing occurred at high rotation speeds. These results can provide a reference for the design of new high-speed rotating conductive joints.
查看更多>>摘要：To clarify the inducing factors and mechanisms of geological disasters, such as large deformation and tunnel collapse, tunnels with layered and soft rock in the Luang Prabang suture zone were examined in this paper. Based on an investigation and summary of the disaster characteristics of tunnel deformation, the excavation loosening zone and geo-stress conditions were field-tested by using a sonic detector and a hollow inclusion strain gauge to analyse the correlation between the surrounding rock deformation and the extent of the excavation loosening zone and geostress distribution. The results show that, influenced by the Luang Prabang geological suture zone, underground water and the mechanical characteristics and occurrence of the rock mass, the surrounding rock mass deformation presents obvious asymmetric features. A large deformation of the rock mass more easily occurs at the tunnel crown and right spandrel (waist), and the main deformation phenomena are the spalling and cracking of shotcrete, buckling and bending of the steel arch and large horizontal convergent deformation. According to the sonic velocity monitoring of the rock mass, the scope of the excavation loosening zone of the rock mass is approximately 5.5 m to 7 m, which is beyond 60% of the tunnel width. Based on the field geostress test, the tunnels in plate suture zones bear intensively horizontal tectonic action, and the maximum lateral pressure coefficient of three tunnels is more than 1.5 (σ1/σ3). Thus, the horizontal convergence deformation and supporting structure failure of the tunnel are serious. Some controlling measures were adopted to release and control rock mass deformation, such as improving the advance support structure, enhancing the steel arch strength and increasing the allowed deformation of the rock mass. Moreover, asymmetric support design, such as local borehole grouting and temporary horizontal support structures, also be implemented. Additionally, the optimal design of rock bolt installation and grouting reinforcement depth should be given more attention during tunnelling.
查看更多>>摘要：In-depth microstructural characterization and structure-property correlations with the number of cycles of the cyclic heat treatment (CUT) were investigated after conducting CHT at 850 °C for 3, 5, 7, and 9 cycles. Each cycle of the CHT involves heating to 850 °C at 5°/s, soaking for 5 min, and then cooling to 0 °C at 50 °/s. Due to the short duration holding, some martensite remained incompletely dissolved at the interface of delta ferrite and martensite matrix which was observed as partially dissolved martensite (PDM). The dissolution and fragmentation of delta ferrite reduced its size and the fraction from the microstructure. The reduced delta ferrite in the microstructure increased the tensile strengths significantly but it deteriorated the tensile strengths on the further reduction of its content beyond 9.5%. The increased microhardness of the martensite phase in the treated specimens was predominantly attributed to the increased dislocation densities. The treated specimens were observed to have 67% higher slurry erosion resistance due to their better combination of hardness and tensile toughness. The material from the treated specimens was removed by ploughing, craters, pull-outs, and microcutting which characterizes a mixed ductile-britde mode of erosion.
查看更多>>摘要：Liquid crystal display (LCD) is likely to accumulate charge and incur ESD events due to the insulating glass plate. In our study, an ESD induced failure of interconnects in LCD gate driver on array (GOA) was analyzed. The monochrome pattern test was conducted to locate the failure site. The morphology of the failure site was characterized by SEM, EDS and FIB. Charge accumulation on long interconnects in the VUV-cleaning process, and subsequent discharging damage at narrow interconnect gaps were analyzed to be the root cause of failure. Furthermore, some specimens were designed to validate the analysis, design of experiments was performed to study the effects of the gap space and the interconnect length on the failure severity. Based on the experimental data, a logistic model was developed to model the failure severity, which can help to provide suggestions for designs to reduce the incidence of failures.
查看更多>>摘要：A rockburst is a complex dynamic engineering failure hazard encountered in deep tunnels, which leads to serious casualties, mechanical damage, project delays, and economic loss. To conduct microseismic (MS) warning and safety control of rockburst hazard can reduce the degree of damage and incidence of rockburst failure. Through analysis of the failure behavior and microseismicity of rockbursts of different intensities, the interference factors and causes for rockburst warning were clarified. By introducing the MS energy gradation curve to analyze the completeness of the MS catalogue, a selection method of MS information for rockburst warning was established. Geomechanical conditions, such as the crack initiation level and degree of damage of a rock mass with different intensities of rockbursts, were characterized by using the distribution of MS events based on a MS energy gradation curve. The logarithm of MS energy threshold value is 0.30 for screening MS events for rockburst warning in this tunnel was set. By comparing the difference of the slope of its straight-line segment, its d_(90) value, and other parameters of MS energy gradation curve in the area at risk to the characteristic parameters used for rockburst warning of various intensities, whether the crack initiation level and degree of damage have reached the condition of occurrence of rockburst can be judged, which can provide some assistance and reference for rockburst warning. Relevant results have been applied in the follow-up rockburst warning work in a tunnel, showing a good effect. More than 85% of rockburst hazards can be effectively identified and warnings were issued. The method proposed here can provide support for warning of rockburst accuracy in the excavation of deep-buried hard rock tunnels.
查看更多>>摘要：Accurately evaluating the time-varying mesh stiffness (TVMS) of a mating gear pair is one of the most important aspects in gear vibration dynamic simulation. Existing work on estimating TVMS of helical gears with tooth spalls generally assumes the defects are in flat bottom shape which deviates from the spalling features as observed in curved bottom shape in practice. The cliff like spalling feature results in inaccurate calculation of TVMS of helical gears with such spalls. This paper proposes an advanced method to evaluate the TVMS of helical gears with tooth spalls with curved-bottom features. In the proposed method, the gear tooth is sliced along the center line of tooth spall in order to easily evaluate the equivalent cross-section area and area moments of inertia of the gear tooth which enables the proposed method adapts to tooth spall(s) with curved-bottom features in arbitrary position, angle and size. The proposed method corrects the foundation stiffness errors of existing methods and takes the influence of axial mesh forces into consideration. Its effectiveness on modelling tooth spalls with curved-bottom features for helical gears is validated by FEM (finite element method).
查看更多>>摘要：Graphite plugged bronze has been primarily applied as the self-lubricating part in the tough oilless conditions, and understanding the detailed wear characteristics and the contacting stress evolution of graphite plugged bronze was important to improve its design for the in-service reliability. This study investigated the wear characteristics and contacting stress of graphite plugged bronze sliding plate from the field trial by means of the multiple topographic characterizations and computational analysis. The results revealed that abrasive wear and adhesive wear predominated on the contacting surface of graphite plugged bronze plate, accompanied by the localized fatigue and erosion. Computational simulation well illustrated the increasingly accumulated stress at the boundary between bronze and graphite as referenced with the stress evolution of bronze matrix and graphite plug, which was considered to be the leading cause of aggravated wear over time. Finding from this study provided the primary wear features of graphite plugged bronze component, which had potential application for the further optimization of the structural restoration and tribological issues of graphite plugged bronze.
查看更多>>摘要：High carbon steel wires are susceptible to a detrimental ageing process, known as strain ageing. Strain ageing is responsible for the redistribution of carbon atoms within a wire microstructure. The redistribution of carbon atoms results in changes to the mechanical properties of a wire in service, which can lead to premature failure. Current methods of monitoring strain ageing are destructive, making in service monitoring challenging. Therefore, it is desirable to detect these subtle changes in a non-destructive manner. This paper reports trials of an electromagnetic (EM) sensor designed for monitoring wire samples. It is known that EM sensors are sensitive to microstructural changes in steels, and sensors are being used to monitor phase transformations during hot steel processing and strip properties in cold mills. This is the first reported use of an EM sensor for monitoring strain ageing in high carbon steel wire. Wires were tested using current standard methods (mechanical testing) alongside EM sensor measurements. An initial increase in tensile strength was observed via mechanical testing, whilst the EM sensors measured a corresponding change in real inductance. In more severe ageing conditions, mechanical properties levelled off somewhat, which was also measured in the corresponding EM sensor measurements. EM sensors are capable of detecting the subtle changes caused by strain ageing in a nondestructive manner. Therefore, the development of inline EM sensors have the potential to monitor strain ageing in a level of detail which has not been reasonably achievable with currently available testing methods.
NSTL
Elsevier