查看更多>>摘要：Laser shock peening (LSP) is an advanced surface treatment technique for improving the fatigue properties of various metals. However, its capability in real-engineering-based complex structures is much less reported. In this study, AA2024-T351 with circular holes, which stand for aircraft wing plates connected by bolts, are treated by LSP and then imposed to high cycle fatigue tests. Surface profiles and residual stress evolution are measured on the fatigue specimens. Micro -hardness, wear, and microstructure analyses are carried out on different peening specimens. Although an increment of roughness caused by periodical plastic deformation is detected on the surface, the LSP introduces a hardening layer containing a large number of dislocations, a surface with higher wear resistance, as well as a compressive residual stress layer. These LSP-induced characteristics significantly enhance the fatigue lives of both types of bolt connections we examined. Finally, the underline strengthening mechanisms are discussed from macroscopic to microscopic.
查看更多>>摘要：This paper studies the creep deformation and failure characteristics of a soft rock roadway under the condition of combined support through a model test that lasted for 30 days. Under the action of high stress, the soft rock roadways present a tendency of continuous failure and nonconvergence, and the cross-sectional area shrinks to 52.3 % of the original roadway. The failure of the anchorage zone causes the bolt to lose its supporting function, and the continuous extrusion leads to the cracking of the lining and the shrinkage of the arch. Floor heave is the superposition of geometric deformation and loose deformation. The floor is continuously replenished by the movement of the surrounding rock below and to the two sides and moves upward under the combined action of high-level stress and vertical stress. Finally, the model test conclusion is verified by field tests, and deformation control schemes are proposed.
查看更多>>摘要：In response to the engineering problems often encountered during the construction of mountain tunnels, the aim of this study is to overcome the inability of numerical simulation methods to rapidly predict tunnel construction based on the [BQ] method of classifying surrounding rock grades. Numerical simulations were carried out using FLAC3D6.0 software based on previous empirical formulas for each parameter of the GSI scores and Hoek-Brown criterion. Relying on the Luanlu Highway Tunnel Project, the engineering problems of the Nianpan and Dahongyan tunnels were firstly identified, followed by numerical simulations to quickly obtain construction predictions for the proposed changes, and finally, engineering monitoring was carried out to verify the feasibility of the method. The results indicate that [BQ] = 311 for the water gushing section of the Nianpan Tunnel, which should be changed from Class III to IV surrounding rock and constructed according to the support scheme for Class IV surrounding rock, corresponding to GSI[BQ] = 43. The maximum load-bearing ratios of the secondary lining for ordinary Class III, seepage Class III and Class IV surrounding rocks are 24.2 %, 25.4 % and 34.7 % respectively. For the Dahongyan Tunnel, the change in the length of the anchors should be adjusted to from 3.0 m to 3.5 m and the distance of the secondary lining from the excavation face changes from 40 m to 46 m. Moreover, the secondary lining load sharing ratio at the monitoring point of the maximum load of the section secondary lining generally doesn't exceed 35 %. The method can be used as a reference for other tunneling problems.
查看更多>>摘要：Tramcar vehicles collect the required electrical power from the overhead contact line by means of a pantograph that carries a pan head with collector strips in sliding contact with the contact wire. Therefore, any failure of pantograph or of its components has a direct effect on the correct tramcar operation. The paper deals with a case of unexpected failures occurred on a connection element of the articulated frame of the pantograph of tramcars, causing the interruption of the service. No evidence of impact with the overhead line was detected, only it was clear that the immediate cause was the fatigue failure of a pin of the articulated connection between the upper and the lower arms of the frame of the pantograph. To clarify the original cause of the fatigue failure, an approach combining field measurements, laboratory tests and data processing to obtain the stresses acting on the pantograph failed components under service condition was adopted. It was found that the pantograph was subjected to high level of vibrations coming from the vehicle carbody, mainly due to the track irregularity. A comparative failure analysis was carried out and a solution to upgrade the component subjected to failure was proposed and implemented.
Santos, Leonardo dos Santos eSoares, Werner Kleyson da SilvaFilho, Paulo Roberto Campos Flexa Ribeiro
14页
查看更多>>摘要：Pipe conveyors are specially designed equipment for bulk solids handling in rough terrain regions or environmental-sensitive processes. Their structures are typically exposed to the weather, which allows dust and rainwater to access the idlers sealing along the conveyor, favored by the geometry of the panels. The steel idlers are manufactured by machining, welding, and assembling processes and tightness-test standards are performed to assess the sealing effectiveness. However, current methods do not address specific pipe conveyor characteristics or predominantly stationary conditions, such as seasonal shutdowns and long spare-part storage time. This study proposes an accelerated weathering method for investigating the influence of rainwater on the useful life of steel idlers applied to seasonal operations of pipe conveyors. A measurement apparatus was developed and a case study was conducted in a coal-handling system, using chemical oxidizing and rainwater. The results indicated the bearings' moisture-corrosion caused by water ingression and seal compression, due to the absence of seals and axial freedom of the bearings, respectively. The proposed method presented a desirable evaluation strategy using a non-parametric test for small-sampled trials, which covered the sealing design review, storage condition inspection, and test self-assessment. Main preventive actions include sealing redesign and changing idlers' storage procedures.
查看更多>>摘要：Deep learning-based faster identification and classification of foreign objects entrapped in coal conveyor belts is the research topic of this paper. The presence of foreign objects poses a serious threat to the service life of the conveyor belt and the safe transport of coal mines. The paper aims to detect foreign objects entrapped in the conveyed material in advance and provide early warning, thereby safeguarding the safe operation of the belt conveyor and preventing tearing accidents from occurring. Firstly, a new and large conveyor belt foreign objects dataset is established for train and test. Then, based on the higher and faster requirements for camera acquisition frequency and real-time algorithm processing that put forward by high-speed belt conveyors, the paper implements a deeply lightweight target detection network based on the Yolov4 by improving its backbone and neck to ensure the detection speed and accuracy. Exper-iments show that the improved network proposed in this paper has achieved a highest detection accuracy of 93.73% with the fastest detection speed of 70.1 FPS (frames per second) on proposed foreign objects dataset, which is an improvement of 1.72% in accuracy and 211.56% in detection speed compared to the original Yolov4; Furthermore, by exploring the influence of motion blur on the detection results, the necessity of shortening the exposure time and improving the video frame rate is proved. All this work is of great significance to improve the detection speed of foreign objects identification and is helpful to promote the application of it in the field of edge computing equipment, so as to ensure the safe and efficient operation of belt conveyors.
查看更多>>摘要：In this article is presented a robust and real-time low-cost automated method for detecting and measuring the various distress types of flexible and stone road pavements. The distress detection, classification and measurement are based on the applications of deep learning approach and YOLOv3 algorithm. A dataset for road pavements damage detection with approximately 9,150 images and 15,585 bounding boxes of flexible and stone road pavements damage was first created and then used in the neural networks training phase. The values reached by the metrics used in the research to evaluate the object detection performance (Loss, Precision, Recall, RMSE) prove that the proposed model detects the pavement distresses with high accuracy and precision. The validation of the method was performed by an error analysis obtained by comparing for some case studies the pavement distresses detected with the suggested method and the real ones. The correct detection rate in the pavement distress detection ranges from 91.0 % to 97.3% depending on the pavement and distress types. The effectiveness of the proposed technique in detecting and measuring flexible and stone pavements distress sheds light on new opportunities for carrying out preliminary and exhaustive inspections of flexible and stone pavements using low-cost detection devices and artificial intelligence techniques.
Vidler, JamesKotousov, AndreiHughes, James M.Paradowska, Anna...
11页
查看更多>>摘要：One of the most successful applications of the Neutron Diffraction (ND) method is the evaluation of residual stress, specifically in welded structures, and many examples exists in the literature. The present study explores the feasibility of applying the ND method to the evaluation of early high-cycle fatigue damage (i.e. the damage prior to formation of fatigue micro-or macro-cracks). In metals and advanced alloys early fatigue damage is normally associated with the accumulation of irreversible and highly localised micro-plastic strains. These strains change the micro-strain/stress field on various scale levels. In this study we attempt to measure these changes applying the ND method to G350 steel fatigue samples, which have been relieved from residual stress and subjected to various degrees of high-cycle fatigue damage. Multiple measurements of the strain/stress field in each sample have been undertaken using the ND method with an incoming beam of 0.5x0.5 mm(2). The outcomes demonstrate that it is feasible to evaluate severe fatigue damage using the ND method, and, in general, the severity of the fatigue damage correlates relatively well with the averaged hydrostatic component of the residual stresses measured by the ND. However, more accurate evaluation may require higher spatial resolution (smaller gauge length) and, possibly, a larger number of measurement points to improve the quality of the experimental data.
查看更多>>摘要：Fluid acoustic structure coupling vibration is rare in nuclear power plant (NPP), especially in the stagnant branch of reactor coolant loop (RCL). This paper reports the phenomenon of fluid acoustic solid coupling vibration of one stagnant branch pipeline founding in the hot function test (HFT) of NPP. Field measurement shows that the vibration exceeds the limit value so it is necessary to determine the root cause of pipeline vibration and provide the modified layout. Based on the data of single point measurement, on-line monitoring, knocking test, acoustic modal calculation and modal analysis, the authors obtain the vibration characteristics and laws of pipelines and infers the acoustic solid coupling. The computational fluid dynamics (CFD) analysis and Strouhal number calculation, the inference of fluid acoustic coupling is identified. According to the above inference, the modified layout and the vibration prediction of the modified layout are proposed. After modification the HFT and the power up test was started. The vibration trend was consistent with the prediction, which verified that the fluid acoustic structure coupling was the root cause of the stagnant branch vibration. The amplitude of the modified the stagnant branch pipeline reduced in the whole process of temperature rise. The operation meets the limit requirements. The stagnant branch can operate normally.
查看更多>>摘要：Sulfuric acid pumps serving in the nitrobenzene process failed many times due to the mechanical seal's failure in a chemical plant. To clarify the failure reasons, damage characteristics were examined by visual inspection, scanning electron microscopy, and energy dispersive spectros-copy. Moreover, the possibility of the galvanic corrosion was confirmed by the designed tests, and the effects of the pure sulfuric and mixed acid on the corrosion were also clarified by the im-mersion tests. The results show that the material degrades in the form of intergranular corrosion. The most severe damage locates in the sealing gland, in contact with the static ring seat. Galvanic corrosion is mainly responsible for the failure. The differences in the chemical compositions and the microstructure play an important role in galvanic corrosion. Moreover, some suggestions are provided to alleviate the corrosion based on the analysis above.
NSTL
Elsevier