查看更多>>摘要：For the current traditional vehicle, reliability test specification is difficult to effectively cover the actual service load intensity of the electric drive system (EDS), the existing specification has the problems of insufficient evaluation of extreme operating conditions, the inaccurate definition of the whole life cycle damage target, and weak user relevance. Therefore, this paper proposes a method to construct an accelerated reliability test cycle for EDS based on 300 users' one-year operation data. By extracting the running fragments and constructing the characteristic parameters associated with the dominant failure load of the EDS. Principal component analysis and clustering algorithms identify the running fragments and obtain five typical operating conditions. Based on the unit damage intensity distribution model, the accelerated testing condition for simultaneous assessment of multiple components is selected, and each component's whole life cycle damage target is determined. To further consider the loading sequence of the fragments, a state transfer probability matrix for each condition is established based on the Markov chain model, which implements the condition combination. Using the multi-objective optimization algorithm determines the number of cycles for each condition and eventually compiles the accelerated reliability test cycle of the EDS. In addition, by conducting rig tests to verify the validity of the accelerated test load spectrum and determine the accelerated factor by the testing data. This study provides specific references and technical support for developing and validating the EDS.
查看更多>>摘要：The grounding grid on the outside of the epoxy insulator breaks under the long-term oxidative corrosion of moisture, fails prematurely, and may eventually develop into a breakdown failure. However, the impact of this process has not yet been discovered. In this paper, a 110 kV combined prefabricated cable joint breakdown fault is discussed. Through the inspection and comparative analysis of the faulty joint, it is speculated that the premature failure of the grounding grid causes the breakdown of the epoxy insulator. The fault process can be divided into the grounding failure stage and the insulation damage stage. In this paper, the corresponding two-dimensional electric field simulation calculation model is estab-lished, the fault development process is restored, and the possible effects of different stages is analyzed. The results show that due to the corrosive effect of moisture, when the grounding grid is broken, a floating potential will be generated on the surface of the epoxy insulator. With the expansion of the grounding failure range, the local field strength on the surface of the epoxy insulator is distorted, which will cause partial discharge. When the failure range is 220 mm, the electric field distortion of the joint reaches the maximum value of 23.3MV/m, which will destroy the insulation strength of the epoxy insulator and cause insulation breakdown, eventually leading to an accident. The research results point out the importance of the continuity of the grounding grid, and the improvement measure is proposed to reduce the occurrence of such accidents. The analysis method for cable joint failure case can provide a reference for dealing with similar accidents.
查看更多>>摘要：As a key component of a wind turbine, the pitch bearing suffers from harsh operating conditions and have to endure complex loads. Due to a large contact angle or load, harmful elliptical truncation may result in stress concentration. However, the influence of elliptical truncation on the performance of the raceway has been rarely studied. This paper investigates the effects of elliptical truncation rates on the raceway surface and subsurface stresses under various loads in a four-point contact pitch bearing. A raceway-ball contact finite element model (FEM) considering raceway hardening is established. The results of a raceway contact experiment which utilizes pressure sensitive films demonstrates the correctness of the FEM. The weakening effect of elliptical truncation on raceway fatigue life is analyzed through three methods. The findings provide an insight for controlling elliptical truncation rate in bearing design and fatigue life assessment to help avoiding raceway crushing and early fatigue failure.
查看更多>>摘要：The Locati method for accelerated fatigue testing can be successfully applied in preliminary fa-tigue testing of components and in production quality control. The method uses only one test sample and assumes that the slope of the S-N curve is known a priori. In this paper, a modified Locati method is presented in which the initial approximation of the S-N curve is based on the tensile strength and pseudo-fatigue limit of aluminum alloy 2618-T851. The first natural fre-quency is likely to be excited during the operation of an axial compressor, according to finite element (FE) modal analysis. A total of five axial compressor blades were tested by vibration exciter. The blade was excited at its first natural frequency until it failed due to a fatigue crack. After the natural frequency of the damaged blade dropped by more than 10%, failure was assumed. The fractured blade surface showed two fatigue crack areas, which occurred at the trailing edge of the blade and at the center of the convex blade surface as predicted by FE har-monic response analysis. The proposed method was successfully applied to the quality control of axial compressor blades in production.
查看更多>>摘要：A demountable 'lockbolt' shear connector (LB-DSC), consisting of a short partially threaded bolt that is locked on a steel flange to eliminate tolerance and initial slip issues and a compatible machined tube that can be fastened/unfastened over the bolt to facilitate the easy and fast disassembly process for reuse of all components, was proposed for use in composite floors or decks of buildings or bridges. This paper focuses on the numerical investigation of the structural behaviour of the LB-DSC under combined tension and shear loading. A detailed finite element method (FEM) model considering material and contact nonlinearity was built and calibrated based on previous standard pushout tests on the LB-DSC. The calibrated FEM model was used to investigate the effects of various parameters on tensile and shear behaviour of the LB-DSC, including the concrete strength of slab, the bolt diameter and strength, the steel tube thickness, and the presence and strength of infill grout. The shear resistance of the connector is significantly reduced when a tensile force more than 20% of the tensile resistance of the connector is applied. Design equations for predicting the tension resistance and tension-shear interaction are proposed to expand the application of the LB-DSCs in sustainable steel-concrete composite construction.
查看更多>>摘要：The phenomenon of surface cracks in steering shaft gear after carburizing and quenching was analyzed by combining experimental research, theoretical analysis, and numerical simulation. The chemical composition, crack morphology, non-metallic inclusions, microstructure, microhardness, and forging process were analyzed and studied by means of directly reading spectrometer, metallographic microscope, scanning electron microscope, energy dispersive spectrometer, and micro hardness tester. The evolution process of surface crack morphology was numerically simulated and reproduced with the help of Deform 3D point tracking technology. The results show that linear surface cracks are formed on the surface of the round steel because of Alumina-type non-metallic inclusions, which destroy the continuity of the steel matrix during the rolling process. Surface cracks become arc-shaped due to the regular plastic flow direction of the material and propagate in the depth direction during the forging process. Crack provide a channel for the diffusion of C atoms during carburizing and quenching process, therefore carburized layer with gradient distribution is formed on both sides of the crack. The carburized layer reacts with oxygen during quenching and subsequent tempering, resulting in a certain degree of oxidation on both sides of the crack and the crack tail. Therefore, the surface cracks found in the steering shaft gear after carburizing and quenching are originated from the rolling cracks formed by nonmetallic inclusions of steel. The rolling cracks have undergone further evolution in the subsequent forging and carburizing quenching process.
查看更多>>摘要：Successful application of Cr-Mo steel depends crucially on behaviour of all zones in welded joints, i.e. base metal (BM), heat-affected-zone (HAZ) and weld metal (WM), both at room and working temperature. Different amplitude loadings were applied for testing of specimens without a crack, made of welded joint as a whole and of BM, in order to obtain Woehler's curves and compare their dynamic strength. Amplitude loading was also applied for testing of specimens cracked in BM, HAZ and WM, in order to get fatigue crack growth curves and parameters C and m in Paris law. Results are analysed to get deeper insight into behaviour of welded joints, made of steel SA 387 Gr. 91, under amplitude loading both for room and working temperature.
查看更多>>摘要：This work investigates the effect of manufacturing defects induced by thread rolling on the high -cycle fatigue life of M30 class 10.9 stud bolts. High-cycle fatigue tests of two batches of nominally identical bolts show significant differences in fatigue performance between the batches. Scanning electron microscopy characterisation of defects in the form of rolling-induced microcracks in the thread root reveals a clear correlation between the defect size and the fatigue life of the investigated bolts. It is demonstrated that initial cracks present in the stud threads have a considerable effect on the slope of S-N curves. Numerical fatigue analysis shows good agreement with the experimental data. Electron backscatter diffraction is used to establish a characteristic length of microstructurally short defects in the tempered martensite microstructure. The obtained results shed light on the definition of critical manufacturing defect sizes in bolts as an essential parameter for quality control in manufacturing process.
Samadi, FarzanehMourya, JeetendraWheatley, GregKhan, Mohammed Nizam...
11页
查看更多>>摘要：This paper aims to quantitatively evaluate the residual stress and fatigue life of T-type welded joints with a multi-pass weld in different direction. The main research objectives of the experi-mental test were to test the residual stress by changing direction along with multiple wielding passes and determine the fatigue life of the welded joints. The result shows that compressive residual stress increases in the sample gradually from single-pass weld to double and triple-pass weld. Moreover, the fatigue life of the specimen also gradually improves with an increasing number of welding passes. Performing multi-pass welding in different directions affects the ma-terial's residual stress and fatigue life, which is an essential factor to consider for assuring the strength of the welded joint.
NSTL
Elsevier