查看更多>>摘要：In metro vehicle systems, the dynamic stress and vibration of the bogie frame have a significant impact on the safety and reliability of vehicles. This study presents a fracture failure analysis of the bogie frame for the metro vehicle. The analysis consists of a bogie frame dynamic stress test, a wheel out-of-roundness (OOR) measurement and a vibration transmissibility test of the vehicle which is also used for operational modal analysis of the bogie frame. The field test result shows that the bending of cross beam combined with torsion of side beams(49.5 Hz) which are aroused by the wheel OOR mainly contribute to the fatigue failure of the bogie frame. To investigate the effect of wheel OOR on the fatigue failure of the bogie frame, the multibody system (MBS) model of the metro vehicle was developed. The MBS model accounts for the flexibility of the bogie frame and the nonlinearity of wheel-rail contact. Furthermore, the modal stress recovery method was adopted to study the dynamic responses of the bogie frame. The measured wheel OOR data is used to validate the efficiency of the model and investigate the characteristics of dynamic stress in time histories as well as frequency spectra. Moreover, the dynamic stress of fracture site in the bogie frame with consideration of ideal polygonal wear in radial deviation including different orders and variable amplitudes was investigated. The phase shift of wheel OOR between different wheels proves to be influential in the bogie frame vibration and thus the characteristics of dynamic stress change accordingly. The recommended limit values of wheel OOR amplitude are shown based on numerical results.
查看更多>>摘要：The failure analysis of concrete gravity dams subjected to noncontact underwater explosions (UNDEXs) plays a significant role in evaluating the safety of dams. In this paper, two types of numerical models were developed to predict the failure behavior of a typical concrete gravity dam, i.e., the fully-coupled and semi-coupled model, which can provide a cross validation of the analysis results. The two models were verified by the experimental data and then adopted for the failure analysis. The results show that the shock wave can produce peak value in the blast responses and concentrated damage directly opposite to the explosive source. Even after the energy transmission at the fluid-structure interface, the UNDEX load still had influence on the failure behavior of the dam and can induce a total swelling in the velocity response.
查看更多>>摘要：During the extrusion of pure nickel N6 bar, the H13 steel die suffers huge wear, resulting in poor surface quality of the workpiece, short service life of the die, and high manufacturing cost. This paper uses field extrusion and finite element simulation to study the macro and micro morphological characteristics of the die surface, the subsurface metallographic structure and the composition characteristics. The results show that the wear mechanism at different positions of the die is different during the pure nickel N6 extrusion process, primarily oxidative wear, abrasive wear, and adhesive wear. A gradually thinning oxide layer is formed from the bearing inlet to the outlet surface. The wear is greatest at the exit of the bearing, and plastic deformation occurs, which brings great difficulties to accurately control the surface quality of the workpiece.
查看更多>>摘要：A surface wear prediction method is used to determine the wear rate of the tooth surface. This method employs the Archard's wear model together with the gear contact mechanics model. An equivalent calculation model based on Hertzian contact theory and fracture mechanics is used to investigate crack initiation and crack propagation. The virtual crack extension (VCE) method is employed to analyze the propagation process from the initial crack to occurrences of tooth surface pitting. A life prediction method on the wear-fatigue coupling is developed. The crack propagation process and pit shapes are determined by the iterative analysis. The relationship between service life and the remaining distance from the crack tips to the tooth surface is determined. The damage mechanism of wear-fatigue coupling is explored. The results of the comparative analysis show that the wear of tooth surface affects the cracks propagation characteristics, reduces the service life and even can change the failure mode. The simulated pit shapes and crack propagation process are in good agreement with the results of other literature. The analysis method of wearfatigue coupling damage can well simulate the damage process and predict service life in spur gear.
查看更多>>摘要：Various diseases failures inevitably appear in expressway tunnels in water-rich strata under the long-term erosion of water. In order to ensure the operation safety of Jizhao tunnel which is in Guizhou Province, China, the radar scanning, drilling and coring and laser scanning were employed to illuminate the diseases failures characteristics and the causes of the tunnel failures. Further, a complete set of solutions against cracks, water seepage and inverted uplift and other diseases was put forward innovatively and applied in the actual project. This case study seeks to examine the characteristics and causes of tunnel failure in water-rich strata. The results show that the water-rich strata, expansive soil and the development of surrounding rock joints are the main factors causing the failure of Jizhao tunnel. The cracking and damage of tunnel lining is dense and disorderly, the water leakage of lining is small but long-term, and only some sections have floor heave. The treatment of crack grouting, clay steel belt and low prestressed anchor bolt were adopted to ensure the integrity of secondary lining and rock mass. The method of adding inverted arch, foot locking bolt and bolt grouting taken in this tunnel is to improve the stability of the tunnel structure and alleviate the stress release in the later stage. Transverse drainage pipes and longitudinal drainage pipes were set to ensure smooth drainage. After the treatment scheme is adopted, the disease is effectively controlled and does not affect the normal operation of the tunnel, which can provide a certain reference for the failure treatment of similar tunnels projects.
查看更多>>摘要：Rib-to-deck connections are one of the most critical fatigue-prone locations in orthotropic steel decks. Initiated cracks in the root of a fillet weld in this location can propagate towards the deck plate due to the existence of transversal tension within the deck plate near the cracking area. Such cracks can put the structure in a very critical situation since they can reach their critical length without being inspected. The main goal of this paper, therefore, is to investigate the influence of the transversal tension on the crack propagation direction in this region. For that, one translates the loading and boundary conditions from a 3D model to a 2D model to avoid computational issues with 3D modelling. Then, a 2D crack propagation analysis is performed using XFEM method, enabling the comparison of several repair solutions. To illustrate the proposed concepts, this paper investigates the fatigue problem on a real bridge case study and characterizes the effectiveness of two possible repair solutions to cope with such fatigue issues.
查看更多>>摘要：The sealing system of the roller cone bit indirectly determines the overall service life of the bit. However, the sealing part is one of the most easily damaged components of the roller cone bit. It can improve the sealing performance and service life of the bit and reduce the times of tripping during drilling. According to the results of the sealing failure analysis and the end-face position of the cone, the function of the end-face groove structure is defined as expelling most of the rock debris particles from the end face of the cone. The end-face sand-discharge structure is designed through theoretical analysis. Simulations are performed to study the performance of the end-face sand-discharge structure, verify the feasibility of the end-face sand-discharge structure, and obtain the effects of the structural parameters of the end-face sand-discharge structure on the performance of the structure. In the process, a new method of discrete phase particle tracking using simulation software is explored.
Demeneghi, GabrielRodgers, KristinaSu, Ching HuaMedders, William M....
11页
查看更多>>摘要：Aluminum 2219-T62 and aluminum 2219-T87 plates were friction stir welded (FSW) together for a simulated service life test. The test specimen experienced a premature failure after being cycled an order of magnitude lower than expected, from over 30,000 cycles to 3226 cycles. The failed specimen was investigated through optical microscopy, scanning electron microscopy (SEM), micro-hardness, and differential scanning calorimetry (DSC) to pinpoint the origin of the weakness. It was observed that the failure occurred in the interface between the weld nugget and the aluminum T62, which corresponded to the lowest hardness throughout the weld. Additionally, through fractography of the fracture surface and microstructure investigation of the weld crosssection, it was concluded that a lack of bonding between the weld nugget zone (WNZ) and the base material (BM) coupled with stress concentrators originating from unconsumed material from the first weld pass were the primary factors contributing to the premature failure of the specimen.
查看更多>>摘要：Spur gears are the most common and simplest in the geometric visualization, and are used to transmit motion and torque from the engine to the desired locations at different transmission ratios. Since the gears work in high loading conditions over a long period, the study of the gear faults due to the high stresses becomes important. In this study, the stresses generated at the root of the gear teeth due to bending is determined using finite element method (FEM) and validated analytically using Lewis theory. Further a detailed crack propagation analysis has been conducted with two intermediate backup ratios of 0.8 and 1.5 and allowing the initial crack length to vary as 0.125, 0.4, 0.7 and 1 mm and check the behavior of the crack propagation paths in static as well as dynamic loading conditions. Also the crack propagation path of the initial crack is observed at the orientations of 180 degrees and 225 degrees from the positive x-axis. The analysis shows that as the initial crack length increases there is increase in the stresses been generated. Further for both backup ratios of 0.8 and 1.5 it has been observed that the crack propagation paths shows variation as the initial crack length increases for both static and dynamic loadings and causes a shift from propagating through the rim to propagation into the width of the rim and showing vertical as well as horizontal propagation in higher initial crack lengths.
查看更多>>摘要：The shape of spatial crack is more complex in practice and crack closure will occur due to deformation, which will result in partial contact of the crack surfaces. In previous researches, a simple linear plane assumption for the gear crack trajectory was usually made and the crack closure effect was ignored. Based on the principle of linear elastic fracture mechanics, a threedimensional numerical model of planetary gear train crack propagation considering the initial crack location, ring gear backup ratio and constraint mode is built in this study. Considering the crack closure effect and the obtained crack trajectory, the meshing characteristics (including the time varying meshing stiffness (TVMS) and contact pressure) are investigated. The results indicate that when considering the crack closure effect, the reduction in the TVMS of the cracked gear decreases and the influence of the foundation crack closure effect on TVMS is greater than that of tooth crack closure effect. Appropriately constraining the outer rim of the thinner ring gear can help avoid catastrophic foundation crack, but the TVMS is more sensitive to the change in the backup ratio when only the pin support is restrained. The uneven distribution trend of cracked tooth contact pressure depends on the nonpenetrating crack type.
NSTL
Elsevier