查看更多>>摘要：? 2022The corrosion of lean duplex stainless steel alloys is examined when applied as a construction material in advanced oxidation processes. Both electrochemical and immersion experiments have been carried out when subjecting wastewater to ozone or Fenton oxidation. The electrochemical experiments suggest that the presence of dissolved ozone at the levels tested does not result in an increased pitting susceptibility for none of the alloys included in the research. However, the application of Fenton reagents induces pitting corrosion to the studied lean duplex alloys. The immersion experiments highlight that crevice corrosion occurs during wastewater treatment with both ozone and Fenton reagents.
查看更多>>摘要：? 2022 Elsevier LtdCorrugation is a common rail damage, which seriously affects the safety and reliability of wheel-rail operation. In this study, the rolling contact fatigue (RCF) damage mechanism of an ex-service small radius rail with long-wavelength corrugation was explored. The results showed that the cracks in the side abrasion area propagated parallel to the rail surface with a very small depth due to the severe wear. While the formation mechanism of cracks in the gauge corner area was the ratcheting of material. The cracks propagated to large length along the plastic deformation flow of microstructure and stopped inside the plastic deformation layer. The cracks in the rail top area propagated first along the plastic deformation flow and then turned at the bottom of the plastic deformation layer into the bulk with the direction which was almost perpendicular to the rail surface. The deflection of cracks was due to the presence of the oxides. The presence of residual austenite in the white etching layer (WEL) and slight plastic deformation area beneath the WEL indicated that the main reason for the formation of WEL was the combination of temperature rise and sustained plastic deformation. It is worth noting that a large number of cracks produced by work hardening made the spalling in the trough severer, leading to the aggravation of rail corrugation.
查看更多>>摘要：? 2022 Elsevier LtdAccording to the traits of engine output torque and vehicle longitudinal dynamic model, considering the influence of the vehicle, the dynamic model of the transmission spindle system is established by using the lumped mass model, and the Runge–Kutta is used to solve the model under sinusoidal excitation and step excitation in starting stage, the time–frequency of transmission spindle under two kinds of excitation is analyzed. Modal analysis is used to decouple differential equations and solve the response of a single-degree-of-freedom system. The analytical approach and numerical solution are compared to each other to verify the correctness of the analysis method, the impact of rotating shaft torsional stiffness on the natural characteristics and dynamic load are analyzed, and the fracture mechanism of transmission spindle is further explored. The analysis results show that when the spindle stiffness is asymmetric, the sinusoidal excitation causes the dynamic load on both sides of the spindle and the driving force on both sides of the vehicle track to be inconsistent, the step excitation induces the second-order low-frequency resonance. Under the small damping, the vibration attenuation is slow, the right end of the spindle is broken under two combined excitations. When the stiffness of the spindle is symmetrical, the influence of sinusoidal excitation on both sides of the spindle is undifferentiated, and the vibration caused by step excitation decays quickly. Finally, the theoretical analysis results were confirmed by crack morphology, vehicle test data.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, an analytical method for fast spectral fatigue-life prediction under Broad-Band random loading is proposed. It is based on the power spectral density of stress in the structure and the Rice peak stress distribution of a stationary Gaussian random process. The novel simple closed-form solution employs special HyperGeometric function which analytically describes the transcendent error weighting function between the Gaussian and Rayleigh distributions inherent in the Rice model. HyperGeometric-based solution outperforms other currently existing approximate methods based on the Rice peak distribution, e.g. Chaudhury, Kam, Dover, Chow and Lee, Lü et al. etc. Straightforward computational applicability and fast engineering implementation of obtained general closed-form results is accented throughout the investigation.
查看更多>>摘要：? 2022In order to accurately describe the mechanical behavior of rubber materials, and the uniaxial tensile and uniaxial compression experiments of three common rubber materials of packer are carried out combined with the function requirements of the rubber cylinder of packer. In addition, the sealing performance of the compression packer is studied in the setting stage by using the finite element software based on the investigation and analysis of the hyper elastic mechanical properties and constitutive models of rubber materials in this paper. It is found that contact deformation of the rubber cylinder begins to accelerate as the time increases through the analysis. When the packer completes sealing process, the upper rubber cylinder mainly plays a sealing role, and excessive stress will cause the shoulder of the upper rubber cylinder to be compressed and fatigue failure. The contact sealing performance of expanded rubber cylinder under different radius clearance and different pressure difference is studied. Under the given wall thickness and radius clearance, the limit pressure load is applied, the rubber cylinder is in a safe working state, and the sealing width is close to the contact length of the rubber cylinder, which ensures good sealing performance. Moreover, the rubber cylinder is in a good elastic deformation range without serious backlog.
查看更多>>摘要：? 2022 Elsevier LtdIn this paper, it is first time to study rideability of mechanical elastic wheel (MEW) in damaged conditions and discuss whether the wheel with local damage conditions will be failure during running. This paper is first time to propose a rideability evaluation method of damaged MEW. For getting the parameters about displacement acceleration of rings and tensile force of chains required from the evaluation method, a rigid-flexible coupling model ‘ring model’ of running MEW was established, the solution method of the model was also given by travelling mode superposition method. The ring model was compared with the experiment and finite element method to verify its accuracy. With using the verified ring model, the rideability simulation was analyzed under eight kinds of speeds and six kinds of damaged working conditions. The results show that: MEW with one or two damaged chains still has the receptible rideability and is not failure, and it provides security for the safe driving of vehicles in emergency situations; when damaging three chains, the wheel can be used to run at low speeds, the rideability of wheel at high speeds will deteriorate and the wheel will be failure; the rideability of MEW with axisymmetric chain damage is better than that with neighboring chain damage; it also finds that the simulation calculation time of ring model is much lower than that of finite element method, the time cost will be saved.
查看更多>>摘要：? 2022 Elsevier LtdPulse magnetic induction coil is the core component of electromagnetic riveting (EMR) equipment. Due to the multi-field coupling working environment, it was easy to fail. In this paper, multi-field coupled simulation was carried out to analyze the failure of pulse magnetic induction coil. The current, riveting force and damaged condition in experiment results demonstrated that the model was accurate and reliable. The simulation results showed that the current density was higher at the middle turns because of the eddy current. The Lorentz force, whose radial components concentrated in inner turns and axial components in middle turns, were unevenly distributed. The Lorentz force led to uneven deformation and this nonuniformity of stress deteriorated with the increase of the discharging voltage. The first turn of the coil suffered from greater stress and is more prone to deformation. Besides the Lorentz force, the higher temperature in the center of the coil also accelerated the breakdown of the insulator. In respect of the issues above, a new type of tower coil was proposed to improve the uneven distribution of Lorentz forces and stresses. The simulation results showed that the maximum stress of the coil decreases obviously under the same riveting force.
查看更多>>摘要：? 2022 Elsevier LtdThe failure investigation has been conducted on shot-piston used in injection system of squeeze casting equipment to clarify its failure mechanism. The macroscopic morphology of failed shot-piston showed there were many network cracks on its upper-end surface while the cylindrical surface was seriously worn. Further studies were carried out on the two surfaces respectively. Firstly, the shot-piston upper-end surface was sampled. And the crack distribution and depth were observed. Then, the crack micromorphology was investigated by scanning electron microscope (SEM), and the sampling points inside cracks were analyzed by energy dispersive spectrometer (EDS). The results show the shot-piston upper-end surface produces thermal stress cracks due to the high-temperature thermal cycle, and oxidation occurs in the cracks. The same method was also used for the cylindrical surface failure mechanism analysis. Above all, the cylindrical surface was sampled and the wear morphology was measured. Afterward, the material composition of the bulge on the cylinder surface and the micromorphology were confirmed by SEM and EDS. The results demonstrate the main failure forms are abrasive wear and adhesive wear. The inconsistent thermal deformation of the shot-piston and shot sleeve caused changes in the fit clearance and resulted in friction and wear. Simultaneously, the metal solution and oxygen erode the shot-piston matrix through the furrow, accelerating wear and failure. According to the failure mechanism of different surfaces, shot-piston service life can be extended by optimizing the squeeze casting process, controlling the temperature gradient, and selecting the appropriate fit clearance, which has important engineering significance.
查看更多>>摘要：? 2022 Elsevier LtdPitting corrosion often occurs in wire rope strands under harsh service environments, causes material removal and local stress concentration, and has been an important trigger for the failure of the strands. In this paper, the spatial parameter equations of wires in each layer of a three-layered wire rope strand with a corroded outermost wire are derived. Based on the equations, the high-precision finite element model of the corroded strand with varied corrosion direction into the wire is established with the consideration of the elasto-plasticity of the wire material. Then axial tensile simulations of the strand are performed to analyze the influence of the surface pit on the mechanical properties, including the contact characteristics, the stress-strain characteristics, the elastoplastic characteristics and the axial load-bearing characteristics, of the strand. The results show that the stress concentration is obvious in the corrosion area, and the maximum stress and plastic strain of the strand occur in the pit. The existence of corrosion pit decreases the bearing capacity of the strand, while increases the contact pressure, von Mises stress, and equivalent plastic strain of the strand significantly. The maximum von Mises stress, maximum plastic strain, stress concentration factor, maximum contact pressure and the decrement of bearing capacity increase with increasing circumferential inclined angle of the pit, while decrease with increasing axial inclined angle of the pit.
查看更多>>摘要：? 2022 Elsevier LtdThis study examines the magnetic signal and mechanism of 304 austenitic stainless steel under fatigue. Fluxgate sensor is used to detect the magnetic signal during fatigue. Scanning electron microscope (SEM), x-ray diffraction (XRD), and Lorentz transmission electron microscope (LTEM) are used to study the microstructure's evolution. On the basis of the microstructure results, a mechanism of magnetic characteristics is discussed and demonstrated. In this mechanism, martensite accumulated by phase transformation is magnetized by stress and enhances the magnetic signal. The magnetic signal's trend and mechanism vary in three fatigue stages. In the first stage, the magnetic signal increases rapidly due to the increased content of strain-induced martensite. In the second stage, the magnetic signal increases steadily, and the relative strain-induced martensite content is only 0.6%. The increase in magnetic signal is primarily caused by the accumulated martensite being magnetized by stress. In the third stage, the magnetic signal increases rapidly due to the rapid development of fatigue cracks. Lastly, a differential magnetic signal processing method for detecting fatigue damage failure in 304 austenitic stainless steel is proposed; the proposed method can distinguish each of the fatigue stages. A warning of fatigue failure can be obtained when the results of the differential increase exceed the corresponding threshold value.
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