查看更多>>摘要：? 2022 Elsevier LtdThis paper presents a case study of investigating the cause of tunnel damages during tunneling in silty clay, in which the damages are existed in both ground surface and tunnel lining. The study is implemented by field investigation and numerical back analysis to determine the cause of tunnel damages, in which the field observed funnel-shaped surface subsidence of ground and surrounding soil moving to the tunnel are considered as softening soil body from ground surface until surrounding rocks in the numerical model, and the material parameters of the field monitored softening soil body are respectively taken as 0.8 times and 0.6 times of the original ones. This work confirms that the field observed tunnel damages during tunneling in silty clay can be numerically simulated, which is significantly influenced by the field monitored softening soil body from ground surface until surrounding rocks.
查看更多>>摘要：? 2022 Elsevier LtdComponents in a nuclear reactor like Sodium Cooled Fast Reactor (SFR) are hardfaced with suitable coating material to avoid self-welding of components caused due to liquid metal coolant which acts as a metallic gum. Tensile stresses are observed at interface of base metal and coating due to difference in their coefficients of thermal expansion which leads to thermal fatigue failure at higher operating temperatures. This reduces the bonding strength between surfaces and also cause delamination of coating. Thus, selection of coating materials with good creep and fatigue life for achieving high breeding ratio and high fuel burn up is important. It is thus required to carry out design of SFR hardfaced components considering the fatigue parameters. This paper gives a review on need to study the fatigue characteristics of SFR components along with need for hardfacing of SFR components. This paper also reviews the fatigue testing methods and fatigue behaviour of various hardfaced materials like low carbon low nitrogen stainless steel (SS), low alloy steels, carbon steels, chromium enhanced steels, high strength steels etc. which are used as materials for different SFR component systems. Fatigue behaviour of cladded components for few other applications is also presented.
查看更多>>摘要：? 2022Bearing plays an important role in operation safety as the key component of high-speed train. The service life is affected by the fracture behavior of bearing during operation seriously. In this paper, the MTS universal testing machine was used to carry out tensile test and tension-unloading test on the sample of the bearing outer ring. On this basis, the fracture process was dynamically monitored by in-situ tensile test. The stress state of the sample during tensile process was calculated by the finite element software ABAQUS. The results show that the microstructure is composed of lower bainite, (Fe,Cr)3C carbides and a small amount of residual austenite. The ultimate strength of outer ring is 2.3GPa. Compared with the center of the sample, the stress triaxiality on the surface is low and the shear stress is high relatively, reinforcing the local plastic deformation. Microcracks are the main damage forms of bearing outer ring. The microcracks nucleate in the three sites, which are the boundary of bainite colony, between the bainite lamellae and around carbide. The bainite colony is the weakest link of the bearing. A large number of microcracks nucleate on the boundary of bainite colony. Under the action of tensile loading, the microcracks propagate along the boundary of bainite colony. With the increasing of load, the cracks propagate unsteadily and lead to the quasi-cleavage fracture of the sample.
查看更多>>摘要：? 2022 Elsevier LtdDuring tunnel boring machine (TBM) tunneling, the violent vibration of the cutterhead system is the major cause of structural failure and engineering accidents. There are many uncertain coupled factors of the cutterhead system, which can lead to inaccurate vibration analysis and difficulty predicting the dynamic response. In this study, coupling dynamic characteristics under multi-source uncertainties of the TBM cutterhead system were analyzed. First, a geological uncertain coupling model and disc cutter uncertain coupling model were established. Then, the load interval boundaries with multi-source uncertainties under different working conditions were obtained and the load interval boundary was combined with the cutterhead dynamic model to establish a dynamic model with multi-source uncertainties. Finally, a dynamic characteristic analysis was carried out using a real-world engineering example to validate the model. The results show that when multi-source uncertainties are considered: (1) The maximum increase in the radial load amplitude and corresponding load interval median are about 137% and 73%, respectively. The maximum increase in the overturning moment amplitude and the load interval median are roughly 92% and 93%, respectively. (2) Under typical working conditions, the maximum increase in the stability vibration response boundary is about 92% for the radial displacement response, with a maximum increase in overturning angle displacement of 70%. (3) The optimum mass fraction of the cutterhead center block is around 46.5%, resulting in the smallest vibration amplitude. The results provide a theoretical reference for the design of cutterhead structures for vibration reduction.
查看更多>>摘要：? 2022 The AuthorsMetal sheet anisotropy is the directional dependence of mechanical properties. It is the key factor that must be considered when using numerical simulation to predict any manufacturing process that involves plastic deformation. The plastic strain ratio, also known as Lankford coefficients or R values, together with the forming limit curves (FLC), are industry standards for assessing the formability of sheet metals. Complete experimental data used in forming the simulation rarely exists. The current investigation focuses on obtaining material properties and verification data as inputs for cold-forming numerical simulation. Uniaxial tests are used to describe the stress–strain curves of the S600MC steel sheet in the rolling, diagonal and transverse direction. The 2D Digital Image Correlation (DIC) technique was used to capture surface strains more accurately than relying on the crosshead of the tensile machine. On the basis of the experimental tests results, an anisotropic model of material was constructed, which was later used as input data for a numerical model, which was later validated. An industry example is shown to emphasize how anisotropy affects the formability of metal sheet blanks. Therefore, a comparison between the physical part in the final shape and the results of the forming simulation has been achieved.
查看更多>>摘要：? 2022 Elsevier LtdThrust bearings are undoubtedly one of the essential parts of turbines and compressors. However, there are many cases in which asymmetric load occurs on the bearings due to e.g. thermal deformations, production inaccuracies or a simple deflection of the shaft. The presented research deals with some basic steps involved in comprehensive research related to developing a new self-equalising thrust bearing. It focuses on the design of its most crucial part - lever, which is responsible for the proper equalising functionality. The study aimed to design a new type of lever geometry, create its numerical model, and, through numerical analysis and calculations, predict its useability in real conditions. According to von Mises hypothesis, stresses were evaluated, as well as contacts and stiffness according to Hertz's theory. The lever was modelled in two sizes, which suit the bearings representing the most often used types in powerful machines. For the levers' design and production, the steel 34CrNiMo6 has been used in a refined state with a yield strength of 900 MPa. The results achieved within the experimental static tests and verifications in operating conditions confirmed the correctness of the final geometry design of the levers, its sufficient stiffness, as well as good functionality of the thrust bearing and its reliability.
查看更多>>摘要：? 2022 Elsevier LtdUneven wear is an inevitable wear phenomenon in the braking system of high-speed trains. To avoid the hidden dangers of the aggravation of uneven wear to the safe operation of trains, it is necessary to monitor the uneven wear state in the braking system in real time. The signals caused by the friction interface present high nonlinearity and potentially chaotic characteristics, which require higher performance for monitoring models. In addition, the complex operating conditions of the friction interface and multiple sources of vibration excitation during braking can reduce the monitoring accuracy with only a single sensor. To address these issues, we propose a deep learning-based ensemble model for intelligent monitoring of the brake's uneven wear condition. First, an integrated model based on convolutional neural network and bidirectional gated recurrent unit was developed to learn spatial and temporal knowledge from the training set of vibration noise, vibration acceleration and friction coefficient. Second, the initial weights were assigned to each model, and the validation set of each signal was used to determine the best weights combined with a grid search algorithm. The models were integrated to achieve multi-source information fusion to improve the accuracy of the final decision. Finally, the ensemble model exploited multi-source feature information from different perspectives. It established the mapping relationship between feature space and sample label space and obtained the diagnosis results through the test set. The proposed model effectively unified automatic feature extraction and information fusion, thus enhancing its intelligence and self-adaptability. Various experimental results showed that the proposed method was highly accurate and stable as well as could effectively monitor the various uneven wear conditions of braking systems.
查看更多>>摘要：? 2022 Elsevier LtdPile-prestressed anchor composite structure is widely used in retain engineering, whose stability analysis is mainly based on the slip line passing through the bottom of pile. However, the existing stability analysis is unable to comprehensively consider the actual slip line passing through pile body, pile bottom and the soil under pile. Based on multiple failure modes, a stability analysis model of composite structure considering both the effects of prestress and pile body is established, and the dynamic search algorithm for the model is proposed. We compare the proposed model with the software of LIZHENG deep foundation pit and the existing calculation model and find the effectiveness of our model. It is found that the safety coefficient of the composite structure is directly proportional to the prestress, pile length and pile diameter, but inversely proportional to the pile spacing. Meanwhile, the safety coefficient increases firstly and then decreases with the increase of slip line depth. Increasing the prestress of anchor in the middle and lower part of the slope has a more obvious effect on improving the safety coefficient. The proposed stability model and search algorithm can consider multiple failure modes and obtain the safety coefficient. In addition, it can comprehensively evaluate the stability of the pile-prestressed anchor composite structure retaining slope, which has superior application value.
查看更多>>摘要：? 2022 Elsevier LtdDrilling and blasting operation is often required to excavate the infrastructure slopes for enhancing their stability or creating space for upgradation. While conducting blasting, there are many incidents of slope failure or rockfall. Thus, proper planning and careful designing of different blasting parameters are essentially required to reduce the incidents of slope failure or rockfall. In the present research, the efficacies of three machine learning (ML) techniques; Logistic Regression (LR), Classification and Regression Tree (CART) and Random Forest (RF) were examined for predicting the blast-induced slope failure (BISF) or blast-induced rockfall during reconstruction of slopes on railway route. 490 databases with thirteen variables were considered for the prediction of BISF. By applying Multicollinearity and LR technique based on minimum Akaike Information Criterion values, the six most influential input parameters were identified. With the selected input datasets, fivefold cross-validation was carried out on randomly selected five sub-groups of datasets using LR tool. Then, the best LR model having the highest prediction rate was selected and with the same training and testing datasets of the selected model, the CART and RF models were also developed. The various performance indices such as correctness, recall rate, precision, specificity, F-beta score, receiver operating characteristics (ROC) and area under the curve (AUC) were calculated to evaluate the developed models' accuracy and applicability. The developed models showed good prediction abilities, with the RF model having highest performance in terms of recall rate (90%), accuracy (96.94%) and F-beta score (0.882). The LR model has higher precision (88.9%) and AUC value (0.96) than CART and RF models. The findings of the research work demonstrate the applicability of all three models in selecting the blast design parameters to prevent BISF during blasting. The use of developed models would result in saving the commuter's lives, avoiding traffic delays and minimising property damages in similar situations.
查看更多>>摘要：? 2022This paper analyzed the performance changes of an engineering ship with mooring line failure. The nonlinear numerical model of the hull-mooring system was established through a fully coupled dynamic analysis program - ANSYS/AQWA. At a certain time, one of the four mooring lines was intentionally disconnected. The dynamic responses of the ship, the mooring line tension and the transient effects of the slow-drift motions with mooring line failure were investigated in detail under the environmental conditions. After a series of numerical simulations were conducted, the results showed that the accidental failure of one mooring line changes the watch circle of the ship and causes the tension redistribution of the damaged mooring system. In addition, the results also indicated that the current practice should consider the transient effects after the mooring line breaks because it may cause the transient overshoot of the slow-drift motion. Consequently, it is necessary to evaluate the safety condition of the ship with mooring line failure in advance. This study could give a profound understanding of the influence of mooring line failure and have reference value in the design of the mooring system.
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