查看更多>>摘要：? 2022The support structure of deep buried tunnel often encountered bias load of during construction in weak layered strata. This paper studied the support structure failure behavior and surrounding rock deformation mechanism with Wuduxi Tunnel as an engineering case. The tunnel presents the damge phenomenons such as primary support cracking, steel arch distortion, secondary lining sidewall extrusion under asymmetrical load and high geostress. Firstly, the laboratory test was producted to research the engineering characteristics of the broken phyllite. The field test results show that the surrounding rock pressure is unevenly distributed around the tunnel, the primary support is all under pressure and the secondary lining is partial in tension. The surrounding rock pressure distribution shows an ellipsoidal distribution consistent with the trend of the rock stratum. The maximum vault settlement and horizontal convergence are 165.58 mm and 282.56 mm, respectively, and the convergence rate is far more than the stable deformation rate in the specification, which proves that the existing specification is not applicable to the large deformation deep buried bias highway tunnel with soft rock. Furthermore, the construction methods of “double primary support-secondary lining” are proposed to control the large deformation of surrounding rock. The field test is carried out to verify the feasibility of the double layer primary support. The field test show that the large deformation can be effectively controlled, and the support structure was stable without crack and damage, which ensured the construction safety of the deep buried bias tunnel in broken phyllite.
查看更多>>摘要：? 2022 Elsevier LtdThe compressive arch action (CAA) is a critical force-transfer mechanism to mitigate the vulnerability of progressive collapse for reinforced concrete frames. To deeply analyze the mechanical behavior of concrete beam-column sub-assemblages under a middle-column-removal scenario, the progressive collapse tests and numerical simulations were accomplished, in which the stress distribution and the force-flow characteristic under CAA were revealed. To accurately evaluate the peak capacity of CAA, a mechanical model of a reverse-curved compressive arch (RCCA) is put forward. The theoretical formulas are derived on the basis of the model, considering both the bending deformation and the axial deformation of the arch. The theoretical calculation results (including the peak capacities and the corresponding displacements) agree well with the experimental results of 20 specimens. Moreover, a parametric analysis on CAA peak capacity is investigated considering the following factors: the axial and rotational restraint stiffness of end supports, the initial connection gap of test setups, the depth-to-span ratio of beams, the concrete strength and the reinforcement ratio of beams. The research results demonstrate that the relative axial (rotational) restraint stiffness should not be less than 1 and the initial connection gap should be less than 1.0 mm to ensure sufficient boundary constraints. According to the parametric analysis results, a simplified formula for CAA peak capacity is established, in which multiple influence coefficients are proposed for the formula. The proposed formula is practical and simple to apply because no iteration or derivation is required, and good calculation accuracy is also verified by 20 specimens. Based on the formulas, the CAA capacities of different column-spacing concrete frames designed with various depth-to-span ratios of beams are compared with the necessary gravity loads. The research results show that the larger the depth-to-span ratio, the greater the bearing capacity margin.
查看更多>>摘要：? 2022The stress relaxation behavior of metallic materials has great influence on its mechanical properties under service conditions especially with high temperatures. This paper proposed a new engineering type of stress relaxation prediction model based on continuous damage mechanics and the second law of thermodynamics. Stress relaxation experiments of nickel-based single crystal DD6 were carried out at different temperatures. The proposed model was verified by experimental data of DD6 and other metallic materials, the results show that the model has good prediction accuracy.
查看更多>>摘要：? 2022We study the structural response of concrete weight coating of offshore pipelines subject to various loading conditions by utilizing the Lattice Discrete Particle Model and Finite Discrete Element Method in a comparative manner. We use laboratory experiments to validate our numerical simulations. We discuss the framework in detail, experiment setups, and outline the capabilities and limitations of both methods. A parametric study with a correlation to the size effect is also presented. We simulate Uniaxial Compressive Strength, Brazilian Disk and a three-point bending of a beam with a notch in both methods. We observe that strength and macroscopic fracture patterns fit well between numerical and experimental methods. We discuss the effectiveness of the methods concerning the transition of size effect, as well as comparing to the size effect law. Our statistical analysis quantifies the capability of capturing the size effect in both models. Capturing the size effect helps to increase the accuracy of predicting the structure response and performance which in turn a key factor in durability of concrete structures.
查看更多>>摘要：? 2022 Elsevier LtdWith the development of typical additive manufacturing SLM, SLM Ti6Al4V has the potential to be used in high temperature vehicle structure. Mechanical properties after thermal exposure and creep performance of SLM Ti6Al4V and its build direction effects need to be studied in detail. In this paper, tensile and creep samples with 0°, 45° and 90° three build directions were designed and manufactured by SLM. Tensile tests were performed after 500 ℃ and 600 ℃ thermal exposure; And creep tests were carried out at 450 ℃ for all samples. The tensile properties after thermal exposure and the creep behaviors were studied and compared. The same size forged Ti6Al4V samples were manufactured and tested. It was shown that the yield strength (YS) and the ultimate tensile strength (UTS) of forged samples increased 24.23% and 16.70% after 500 ℃ exposure; while YS and UTS decreased after 600 ℃ exposure. The build direction had a significantly effect on the tensile ductility of SLM Ti6Al4V after thermal exposure. After 500 ℃ exposure, the tensile property of 90° sample was the best. Although the strength of 90° sample was slightly lower than that of 0° sample and 45° sample, the elongation was about 36.7% higher than that of 0° sample and 45° sample. After 600 ℃ exposure, 90° sample had both the highest strength and the elongation. Compared with forged samples, the SLM samples had longer creep ruptured time but lower ductility. For the SLM samples, 45° samples had best creep properties, while the properties of 0° samples were the worst. Fracture surfaces, failure modes and effects of build directions were investigated. Based on the features of SLM microstructures, two improved constitutive models were proposed and can be used to predict the anisotropic behavior of SLM material.
查看更多>>摘要：? 2022 Elsevier LtdOwing to the different pH values of water resources in different places, it is not practical to design hydraulic–mechanical magneto-hydraulic sealing devices under clean water conditions. This study used a Venturi structure to analyze the relationship between the solution pH and cavitation. A high-speed camera and turbine flowmeter were used to record the primary cavitation flow rate, shedding period of the cavitation cloud, and flow direction length of the cavitation cloud of solutions with different pH values. The results showed that acidic and alkaline solutions can inhibit the occurrence of primary cavitation. Compared with clean water, acidic and alkaline solutions have longer cavitation cloud flow length, shortened cavitation cycle, and higher degree of cavitation. In detail, the degree of cavitation in the acidic solution is stronger than that in the alkaline solution. Therefore, the amplitude of the pressure pulsation in an acidic solution should be taken as the reference when designing a hydro-mechanical magneto-hydraulic sealing device.
查看更多>>摘要：? 2022 Elsevier LtdNominal stresses have been used for a long time for the assessment of fatigue resistance of welded joints, however, this approach has strong limitations since the definition of the nominal stress may be subjective for complex welded details and/or complex loading. On the other hand, the hot-spot stress approach has been proposed to overcome these limitations considering the structural geometrical discontinuities. However, the hot-spot stress methods also present certain limitations, and the present study aims at evaluating the available numerical and analytical hot-spot stress methods proposed by DNVGL (2016) and IIW (2014). The particular case of an offshore tubular KT joint has been considered herein and discretized in two planes. It has been studied numerically using the ABAQUS software coupled with the hot-spot stress extrapolation methods described in IIW (2014) and DNVGL (2016). The influence of the weld geometry has been considered and evaluated. In addition to the numerical method, the present study has also considered the analytical approach proposed in DNVGL (2016) derived from the combination of Efthymiou solutions for the stress concentration factor with the method of superposition of stresses. The numerical models according to IIW (2014) have been found to be more conservative when compared with the mesh-size methods proposed by DNVGL (2016), both in numerical modelling without the weld or with weld. For the numerical models with weld cord, the mean values of normalized difference index obtained for all braces together, as a result of comparing numerical results with analytical solutions, are lower, when compared with results obtained from the numerical models without weld cord.
查看更多>>摘要：? 2022 Elsevier LtdIn the present work, a parallel numerical and experimental analysis of a critical type of defect is conducted, the shear deformation which is caused by the thermoforming process of thermoplastic-based composites reinforced with glass fiber textile. The numerical analysis is conducted a priori using a commercial finite element software, developed for this specific process. In parallel, an experimental thermoforming test was conducted using the exact same parameters used for simulating the process and, consecutively, measurements of the component characteristics such as the fiber relative deformation of the textile are taken. Aiming to validate the simulation and to obtain crucial information about this phenomenon, a comparison between the finite element process simulation and the measurements output is conducted revealing a satisfying agreement between them, leading also to useful conclusions about the validity of the simulation method as well as about the detection and measurement of the shear textile deformation using optical systems.
查看更多>>摘要：? 2022The instantaneous contact welding failure refers to the phenomena that the opening time of relay exceeds the threshold value after the de-energization of coil. The direct consequence is the significant increase of switching time of electric circuit. Understanding the features and mechanisms of instantaneous contact welding is beneficial for the failure analysis and further optimization of relays. In this paper, the electrical endurance experiment of ac general-purpose relay is carried out until the cumulative number of instantaneous welding failure reaches five times. The contact re-close phenomena in the strong welding condition are observed by using the contact voltage and dynamic force waveforms, and the effect of peak voltage, point-on-waveform (POW) and breaking delay time of contact re-close on the welding force are investigated explicitly. Finally, the possible breaking process of two types of contact re-close (melting re-close and boiling re-close) are presented based on the degradation of the contact surface morphology. It is determined that the evaporation of contact a-spots or the converging of molten metal bridges would be the root reasons for the welding in the breaking process, and the material transfer behavior results in frequent instantaneous welding failures at the end of experiment.
查看更多>>摘要：? 2022 Elsevier LtdThe spherical plain bearing is an important basic moving component which is widely used in aerospace and industrial equipment. However, current studies are predominantly conducted on gasket-type bearings, with only a few on the failure behaviour and mechanism of the coated spherical plain bearing. In the present work, the wear failure behavior of GE17ES coated spherical plain bearings is investigated using the whole life and stage life test methods. Furthermore, the mapping relationship between the macroscopic torque change and the micro-structure evolution of the bearing friction surface in each life stage is analyzed using the microscopic characterization method. The results indicate that the torque signal can reflect the service state of the bearing comprehensively. More specifically, during the normal service stage, the smooth area of the coating ensures the stable operation of the bearing. Conversely, during the signal mutation stage, the accumulation of damage on the substrate surface causes rapid failure of the bearing. In summary, the main wear failure mechanism of the bearing includes plastic deformation, abrasive wear and adhesive wear, and oxidation wear may accelerate its failure. These results revealing the damage and failure evolution process of the coated spherical plain bearing, could provide a theoretical reference for future studies on the wear failure of coated spherical plain bearing.
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