查看更多>>摘要：Stringent requirements in emissions and the depletion of conventional fossil fuels drive the development of Gaseous Alternative Fuels (GAF). As a commonly used power source, compatibility issues of the internal combustion engines under the harsh conditions created by the fuels become a technical barrier to improving the safety, reliability, and power performance of real world engines' applications. This paper systematically reviewed the material performance affected by GAF from the perspective of crucial engine components. Issues related to the compatibility of crucial components with GAF were firstly summarized in corrosion, thermal damage, and wear. Experimental study progresses concerning these compatibility issues and the assessment criteria for the material performances were discussed. Feasible critical technologies for improving material performances were discussed from tribology. Finally, this review briefly discussed the characteristics and plausible future trends for these compatibility issues. This study provides technical assistance for the safe application of GAF on internal combustion engines.
Pacheco-Cherrez, JosueFortoul-Diaz, Jesus A.Cortes-Santacruz, FroylanAloso-Valerdi, Luz Maria...
15页
查看更多>>摘要：Despite the recent advances in supervised ML-based methods for fault bearing detection is that most published work uses only vibration data for damage detection. However, depending on the type of bearing failure and the frequencies of the signals, the combination of non-invasive techniques such as vibration signals and acoustic signals can be an alternative to increase the precision when detecting a failure. In this research, simulated faults were created in a healthy bearing. Most of the values from defect areas are between 0.007 and 0.014 in. of diameter. A database was generated from these bearing faults, so that the acoustic and vibratory signals of the same fault condition could be compared, and a better diagnosis could be made. For this, an experimental system was designed. The present work, therefore, describes and compares three different supervised Machine Learning-based methods based on acoustic and vibration data. So far, there have been two approaches to obtain data. For this work, acoustic and vibration data were obtained from an own experimental system, integrated by transducers (microphone and a tri-axial accelerometer), data system acquisition, and a signal recording system. The three different methods proposed in the present work achieved a fault classification above 96%, thus presenting a new versatile approach to enhance predictive maintenance methodology in a rotary machine with vibration and acoustic signals.
查看更多>>摘要：In the gear transmission system, tooth root crack often occurs due to the impact of machining technology and cyclic load. The appearance of tooth root cracks will affect its mesh stiffness and change the vibration characteristics of the system, thereby reducing system reliability and service life. In previous studies on the modeling of the mesh stiffness of cracked gears, the cracks were often supposed to be in a closed state, and the elastoplastic deflection of the fault gear teeth was also neglected, resulting in significant errors in the estimation of the mesh stiffness. When a tooth root crack occurs, the engaged gear teeth will deviate from the theoretical meshing position due to the elastoplastic deflection of the fault tooth. Therefore, an accurate mesh stiffness estimation model in view of the opening crack and elastoplastic deflection of the cracked tooth is put forward in this study. Firstly, the actual meshing position of the tooth pairs is derived considering the elastoplastic deformation in the crack opening state; Then, the improved potential energy method is adopted to calculate the mesh stiffness, and the finite element method (FEM) is applied to verify it. At last, the influence of failure severity and elastoplastic deflection degree on mesh stiffness and load sharing is analyzed. The results show that the severity of the crack failure and elastoplastic deflection has a significant impact on the mesh stiffness and load-bearing. This research can provide stiffness input for the study of fault dynamics of the gear transmission system.
查看更多>>摘要：The nonlinear stability control of surrounding rock with large deformation is the key issue in realizing rapid excavation of deep soft rock roadway. Combined with various research methods, this paper deeply analyzes the characteristics of instability. Through the modified DruckerPraeger criterion, the mechanism of roadway instability under the coupling actions of multiple factors is studied, and the control strategy of deep soft rock roadway is given. On this basis, the combined support scheme is optimized and verified by simulation, test and field application. The results show that: (1) Long aging, strong rheology and full section are the basic characteristics of deep soft rock roadway convergence. High resistance and yield are the inherent requirements of nonlinear large deformation roadway support. (2) The asymmetric support of roof and floor violates the objective law that the floor heave of deep soft rock roadway is larger. (3) Roadway instability is the result of comprehensive action of internal and external factors, which reflects the gradual deterioration process of the rock mass. The purpose of the support is to effectively improve the bearing capacity of the surrounding rock and avoid this process. (4) It is an effective measure to improve the support efficiency and an important way to realize the stability control of nonlinear large deformation roadway by combine the parts organically and coordinate their bearing performance.
查看更多>>摘要：As the core component of an internal mixer, the rotor is subjected to friction from rubber and its filler during the mixing process, which causes the surface of the rotor to wear and can also affect the gap between the rotor edges as well as the gap between the rotor and the mixing chamber wall. The more significant the rotor wear, the larger the gap between the rotor ribs and the wall of the mixing chamber, which results in weaker shearing effect of the rotor on the rubber and even leads to uneven dispersion of filler in the rubber, eventually affecting the mixing effect and mixing quality of the glue. In this study, based on the viscoelastic solid theory of the rubber mixing process and the friction mechanism between rubber and metal, combined with the discrete element method, a dynamic simulation model for the wear of the synchronous quadrilateral rotor of an internal mixer is established. The simulations are performed in the EDEM software, and the results are analyzed and compared under different mixing parameters. Further, a control experiment is established to verify the feasibility of the proposed dynamic model for rotor wear.
查看更多>>摘要：The coal mining process may make cracks in the floor to connect the confined aquifers, causing water inrush from the coal seam floor. Through the inclusion theory and compression failure criterion, the failure model of floor crack structures in deep mining is built by adding the additional water pressure. Under the compressive stresses, the additional water pressure in the cracks increases linearly as the mining-induced stress and the mining depth increase. As the confined water pressure rises, the failure strength of the floor crack structures decreases linearly, while the growth length increases nonlinearly. Yet, the failure strength first decreases and then increases as the angle of crack structures increases, and the dominant failure angles of crack structures in the floor range from 30 to 70 degrees. Thus, the various dynamic monitoring technologies of crack structures, such as water-rich area detection, hydrological and micro-seismic monitoring, and failure depth exploration in the floor, are improved on the mining site. And these technologies are combined to establish a reliable early warning system for floor water inrush, and provide a safe guarantee for deep mining under high confined water pressure.
查看更多>>摘要：During operation, various physical and mechanical processes occur in the metal of the rails under cyclic force action over time: plastic deformation of the rail rolling surface, the formation of internal and surface cracks, changes in residual stresses, etc. As a result, the mechanical characteristics degrade and the performance of the rails decreases. A microstructural analysis of the cross-section surface of six rails with internal cracks-longitudinal and transverse ones-has been performed. The rail samples were taken out of attendance after many years of service. Fractographic analysis of the crack surface and the surrounding material indicates a significant degradation of the physical and mechanical properties of the rail steel and intensive structure formation during long-term operation of the rails. The added value of this research is analysis of the fracture surfaces taken from components in service.
查看更多>>摘要：Surface coatings are used to change the characteristics of substrate material and improve its superficial properties based on materials and applications. This paper aimed to characterise and improve different Cu-GnPs coatings realised through electroplating on a copper substrate. Two different kinds of coatings GnPs were produced to realise a superficial self-lubricating effect for friction control applications. The realised coatings were characterised by using scanning electron microscopy (SEM) and profilometry to evaluate the differences between tribological and morphological properties, check the influence on the wear resistance, and scratch behaviour. The results were compared with the ones obtained with a coating with the same thickness of pure copper and as it is Cu substrate, and showed a higher wear performance of the reinforced coatings. The authors propose that between the friction pair, the GnP establishes a graphitic transfer film that protects the surface from wear with its lubricant effect.
查看更多>>摘要：High strength quenched and tempered alloys are used in the manufacture of leaf springs, and peening techniques are used to induce compressive residual stresses on the tension surface of the individual leaves to resist fatigue crack growth. However, the extent of such residual stresses is usually limited to around 0.1-0.2 mm deep. Their beneficial effect can therefore be negated by corrosion pitting, while high strength steels are known to also be susceptible to environmental embrittlement in high chloride environments. This case study deals with an interesting example of environmental embrittlement of multileaf springs reportedly made from 60Si2Mn steel, but actually manufactured from 51CrV4 steel. Multiple cracks initiated from corrosion pits and fatigue failures occurred within 6-9 months from service entry of the vehicles. The embrittlement was triggered by the disinfecting and cleaning regime that reflected the use of the trucks for conveying animal feed.
查看更多>>摘要：Reservoirs and dams often play critical roles in economics and politics. They are frequently considered as the primary targets during wartime or in terrorism attacks. In this study, the behaviors of concrete gravity dams subjected to underwater explosions are numerically investigated. Three-dimensional finite element models are developed according to the design drawings of a concrete gravity dam built in China. The effects of an underwater explosion, including the shock wave and bubble oscillations, are modeled based on the pressure time-histories. The water is modeled using the acoustic method, for which the propagation of the pressure histogram is well reproduced as an acoustic wave. The concrete dam is modeled using solid elements. The damage and failure of the concrete are reproduced by the damage-plasticity model with strain rate dependence. To investigate the influence of bedrocks, three types of numerical models are developed, which are validated by comparing the predictions with the centrifuge tests on a scale concrete gravity dam. Systematic numerical results indicate that the developed numerical model is capable of capturing the features of concrete gravity dams subjected to underwater explosions. Furthermore, the bedrocks play an important role in the dynamic responses of the dams. Thus, the bedrocks should be considered for the accurate modeling of the underwater explosion systems of concrete gravity dams.
NSTL
Elsevier