查看更多>>摘要：? 2022 Elsevier LtdThe overheating phenomenon of slip ring will lead to wear failure of friction pair, and further affect the current-carrying efficiency. In order to study the temperature properties of slip ring, a friction and wear model with electric currents applied was established by COMSOL. The accuracy of the simulation was verified by the experiments. The distribution of coupling temperature field, and the influence of sliding speed, electric current density and contact pressure on the coupling temperature were studied. A phenomenon of “high temperature tailing” appears behind the contact area, and the trail length increases gradually with the time. The coupling temperature increases with electric current densities and sliding speeds. The MCT decreases rapidly at first and then increases gradually with the increase of contact pressure. There exists an optimal contact pressure to minimize the MCT. The optimal contact pressure increases with electric current densities, and decreases with sliding speed. The results may provide a theoretical basis for the temperature rise analysis and can improve the current-carrying efficiency of wind power slip ring.
查看更多>>摘要：? 2022 Elsevier LtdThe research aims to illustrate a vulnerability approach extended for the aggregate masonry buildings belonging to an urban area of the city of Latronico (Basilicata Region). The area was examined taking into account the predominant building typology according to the investigation line WP2 “Inventory of existing structural typology” of the Italian ReLUIS project. The propensity at damage of the masonry stock was done according to a survey form conceived for clustered typologies. A damage scenario was provided according to the hazard map concerning the study area. To this purpose, three seismic events were evaluated with variable magnitudes and epicentre distances, by adopting a seismic intensity prediction equation. Fragility curves were estimated relating the macroseismic observation to the PGA, providing an overview of the asset exposed at risk. The achieved outcomes were discussed in relation to the fragility functions concerning the BTM, highlighting the differences in terms of the expected damage.
查看更多>>摘要：? 2022 Elsevier LtdThe aero-engine rotor system is connected by one or more stages of mounting edges through bolts, and the pre-tightening state of the mating surface will directly affect the dynamic performance of the rotor and even the whole machine. However, there is little research on the identification method of the pre-tightening state of the mating surface of the disk-drum rotor with a multi-bolt flange connection. Therefore, based on the vibration theory, this paper analyzes the feasibility of the pre-tightening state identification method of the mating surface. Then, from the perspective of the assembly process and structural characteristics of the rotor system, this paper takes the high-pressure compressor disk-drum rotor, high-pressure turbine disk-drum rotor, and high-pressure rotor system as the research objects, respectively, and uses the finite element method and experimental method to analyze the influence of the pre-tightening state change of the mating surface on the rotor dynamic characteristics. Finally, according to the obtained regularity cognition, three pre-tightening state identification methods of multi-bolt connection mating surface are proposed: low-order vibration phase difference method, amplitude variation method of higher-order frequency response function (FRF), and axial tension-sensitive natural frequency offset method. The proposed methods can effectively identify the preload state of the mating surface of the disk-drum rotor in engineering due to improper assembly or harsh environment and provide a new research idea for the dynamic characteristic detection and assembly quality evaluation of aero-engine rotor.
查看更多>>摘要：? 2022 Elsevier LtdAiming at solving the problem of premature fatigue failure of the bogie frame of a metro vehicle during service, this paper mainly studies the method of accurately predicting the fatigue life of the bogie frame of a metro train through the measured load. To correct the error between the calculated damage and real damage value, a hybrid frequency-time calibration method is proposed. Based on the quasi-static relationship between the load and stress as well as the basic theory of the multiaxial spectral method, the expression of stress statistics in the frequency domain is derived considering the correlation of multiple loads. According to the damage consistency principle, the NSGA-II multi-objective optimization algorithm is used to calibrate the load system. Based on the frequency domain calibration results, the dynamic stress time history could be acquired by the Inverse Fast Fourier Transform (IFFT) method. The results show that the calculated damage through the calibrated load completely covers the real damage value, and the ratio range between them is 1.10–1.42. The above results indicate that the calibrated load can be used for the reliability design of later structural optimization.
查看更多>>摘要：? 2022 Elsevier LtdThe microstructure and mechanical properties of top plate, force wall and bottom plate in low-pressure sand-casting aluminum alloy cylinder head were evaluated at room temperature. The results of the comparison study showed that with different positions of the cylinder head, the microstructure and mechanical properties were considerably different. For the convenience of analysis and discussion, the quality index (Q) was used to characterize tensile test data, which equals ultimate tensile strength plus 150 log elongation. The top plate has the best tensile performance with Q of 443.5 MPa, while the Q of the force wall (292 MPa) and bottom plate (355.5 MPa) is only 66% and 80% of that on the top plate. The tensile properties of the cylinder head are mainly controlled by dendrite arm spacing (DAS), including primary dendrite arm spacing (PDAS) and second dendrite arm spacing (SDAS). The influence intensity varies with the value of DAS. In general, the tensile properties decreased with the increase of DAS. When the aluminum alloy specimen has small DAS (PDAS ≤ 46.49 μm, SDAS ≤ 33.64 μm), Q increases rapidly with the decrease of DAS. However, when PDAS ≥ 104.33 μm, SDAS ≥ 49.82 μm, the effect intensity of DAS on tensile properties is partially reduced. When the number of cycles is 2.5 × 107, the fatigue stress limits of the top plate (69.2 MPa) and bottom plate (70.0 MPa) are highly comparable, which is mainly due to the similar SDAS and eutectic Si average area. Porosity defects also have a significant impact on fatigue performance. The presence of porosity defects increases the scatter of fatigue properties. In addition, more than 90% of the fractures are caused by porosity defects, which indicates that porosity defects are the main factor causing fatigue cracking of low-pressure sand-casting aluminum alloy cylinder head. Therefore, the casting process should be optimized to avoid porosity defects as much as possible in order to improve fatigue performance.
查看更多>>摘要：? 2022 Elsevier LtdIn this paper, the isothermal fatigue behavior and life of 4Cr2Mo2V steel for new hot stamping die were studied. Axial tension compression symmetric fatigue tests with different strains were carried out at 300 ℃. When the half strain amplitude was from 0.3% to 0.9%, the response stress continued to soften, and the decline rate of response stress gradually increased, but when the half strain amplitude was 0.9%, the material would fail early. Used Coffin-Manson (C-M), Basquin-Coffin-Manson (BCM) and original Ostergren models to predict the life, the prediction effect was not good. Box-Cox variable transformation was carried out on the cycle life, and then the modified Ostergren model could accurately predict the life. The life prediction model was also established by fitting the response stress curve, but the appropriate d value needs to be set to accurately simulate the life.
查看更多>>摘要：? 2022 Elsevier LtdThe corrosion of reinforcement has a serious impact on the life cycle service performance of reinforced concrete (RC) structures. To improve the durability, the use of a bimetallic steel bar (BSB) composed of stainless-steel cladding and carbon steel substrate is suggested. Stainless-steel cladding blocks the contact between the carbon steel substrate and the corrosive environment. The low-cycle fatigue properties of the BSBs were investigated. With an increase in the strain amplitude, the peak stress in the stable hysteretic curve of the BSB increased gradually. Different coefficients were selected to clarify the variation trend of the stress, strain, and energy properties. A fatigue model revealing the relationship between the plastic strain range, cycles to failure, and strength loss coefficient was investigated. The effects of nonlinear mechanical properties and inelastic buckling on the low-cycle fatigue properties of the BSB were included in the numerical simulation.
查看更多>>摘要：? 2022 Elsevier LtdTransformers are key players at transmission and distribution level in electrical grid to deliver reliable, efficient, smooth and quality power at consumer end. Power transformers plays a crucial role in the interconnected power systems and is therefore considered as one of the most important and critical assets. Any deterioration occurring due to electrical, thermal, chemical as well as environmental stresses can be identified from health indices and immediate actions can be proposed to avoid any premature failure. This research paper includes the multi criterion based mathematical approach to identify the health indices of power transformers. The proposed approach gives more precise result compared to the conventional methods used for transformer faults diagnosis like gas ratio and traditional experiment based methods to measure health index. The multi criterion considered here are dielectric strength, acidity, breakdown voltage, dissolved gas analysis, furan compounds, dielectric dissipation factor, moisture presence, interfacial tension, winding DC resistance, tan delta etc. It becomes more reliable and proficient to measure the health indices using multi criteria decision making along with piece wise linear equations and Residual Analysis approach for accurate measurement for newly manufactured transformer as well as in service aged transformers. Further, 100 test data set have been added to analyze the performance and implications of health index of 20 completely healthy transformers, 60 partial deformed transformers and 20 complete deformed transformers or on verge of failure. This work gives detailed insights of health status and insulation condition of new transformer, in service transformers or any failure transformer.
查看更多>>摘要：? 2022 Elsevier LtdThe significant increase in applications of additive manufacturing has led to various investigations in this field. Three-dimensional (3D)-printed parts might be subjected to different environmental conditions during their service life. Therefore, a profound knowledge on this subject can significantly help to increase structural performance of these parts. In the present study, effects of accelerated thermal ageing on the mechanical behavior of 3D-printed parts has been investigated. To this aim, a natural environment has been simulated and the related effects are investigated by means of accelerated thermal ageing with temperature in the range of ?5 °C to 35 °C. Moreover, the current study describes influence of manufacturing defect on the fracture behavior of 3D-printed components. Since defects and anomalies might be occurred during 3D printing process, fabricated parts can show different mechanical behaviors. In the present investigation, intact and defected test coupons with different raster orientations were printed and examined. In detail, polylactic acid material was used in fabrication of the specimens based on the fused deposition modeling process. These groups of specimens were also aged and subjected to tensile load. The documented results indicate effects of thermal ageing on the structural integrity of intact and defected specimens. The outcome of this study can be utilized for future design and next computational modeling of 3D-printed polymer parts.
查看更多>>摘要：? 2022 Elsevier LtdShafts are core mechanical components of equipment. These play a key role in supporting the rotating device and transmitting motion, torque, or bending moment. The quality and performance of shafts are of high significance for the normal and safe operation of the equipment. Failure analysis is of high significance for the safe operation of mechanical equipment and accident prevention. By identifying the modes and causes of failure, effective measures can be proposed to improve the service life of shafts and eliminate potential accidents. In this work, failure analysis cases reported for shafts in the past 20 years are reviewed. Typical failure modes including fracture, corrosion, wear, and deformation failures are summarized. Fatigue fracture is the most common failure mechanism of shafts owing to the influence of cyclic loads on shafts under normal working conditions. The fatigue failure characteristics, environmental factors, wear fatigue, and causes of fatigue failure of shafts are described in detail. The objective of this review is to provide systematic failure analysis information of shafts and thereby, aid engineering communities to identify the failure mechanisms of shafts under different conditions.
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