查看更多>>摘要：When designing gear systems, it is crucial to select materials to meet functional requirements of the application. It is necessary to know characteristics of the materials that will be integrated into drive components of the entire system to ensure a precise calculation of the system. In gear applications, system performance does not depend on a single material, but on material pairs that form a gear system. Therefore, it is desirable to test gears of different polymer materials to obtain relevant information regarding material data which are integrated into advanced virtual models to optimize mechanical structure. Gears are usually exposed to cyclic fatigue spectrum load, which causes degradation of the tooth flanks shape, and consequently increased teeth flanks wear, which results in lower load-carrying capacity. In this paper, wear behavior of gear pairs POMPA66 and POM-PA66 reinforced with 30% of glass fibres with internal lubricants (PTFE and silicone oil) are analyzed and discussed considering load conditions. The results showed higher wear rate on the POM gears in comparison to PA66 based gears. It has been deduced that wear progression is nearly connected to more elastic material properties related with higher elongation and coefficient of linear thermal expansion for POM material in comparison to to PA based materials. Wear coefficients for POM and PA based materials imply that wear and deformation of gears are inversely proportional with durability. When observing materials at higher loads, it can be noticed that POM/PA66 GF30 TF15 Si has longer lifetime compared to POM/PA66 and vice versa at lower load. The authors concluded that lower wear and deformation of gear teeth have a decisive influence on good durability performance of gears.
查看更多>>摘要：The cutter ring of the TBM disc cutter is the main tool that directly contacts and cuts the rock. The cutter ring is prone to wear during the tunneling process, and the lower wear life will drastically reduce the tunneling efficiency and increase the construction cost. The working temperature of the cutter ring is an important factor affecting its wear resistance. TBM cutter cooling measures do not produce satisfactory results when tunneling in hard rock environments. When the cooling is not timely, the working temperature of the disc cutter ring will reach more than 400celcius. Therefore, this paper carried out the cutter ring and rock wear experiment with water and air as the cooling medium. After analyzing the influence of different cooling methods on the weight loss, the working temperature and the wear mechanism, the result is obtained as follows: (1) The working temperature under water mist cooling is the lowest, and its wear loss is reduced by 65.2% compared with the non-cooling state. Under 30 m/s air flow rate cooling condition, the weight loss dropped by 22.5%. (2) The hardness of the cutter ring material will gradually decrease as the temperature rises. As the working temperature increases, the ploughing wear mechanism with plastic characteristics will appear. (3) The lubrication of water and the drop in the vertical force load after the rock absorbs water are also important factors to reduce the wear of the cutter ring.
查看更多>>摘要：The influence of the decrease in environmental temperature on the wear and tribo-chemical behaviours of wheel-rail materials was studied. The results indicated that, at all tested temperatures, a tribo-film zone, oxidation zone and metallic zone were formed on the worn rail surfaces. The decrease in the temperature could decrease the content of 0 and Fe3+ ions both in the tribo-film zone and the oxidation zone. As the temperature was reduced below 0 degrees C, the tribo-film zone on the rail surface enlarged significantly, leading to a decline in the wear rate of the rail material. With the decrease in the temperature, the embedded wear debris spots on the wheel surface increased and the wear rate of wheel decreased gradually. As the temperature declined from 20 degrees C to -40 degrees C, the wear form of wheel-rail would transform from the severe wear to mild the wear.
查看更多>>摘要：Rail welded joint is one of weak links in high-speed railway, and its dynamic performance has important effects on the safety, stability, and comfort of the high-speed train. In this work, the dynamic mechanical responses at different regions of U75VG rail flash-butt welded joint were investigated. The results show that the base metal (BM), welding zone (WZ), and heat-affected zone (HAZ) of U75VG rail flash-butt welded joint has an obvious strain rate effect, i.e., the material strength increases with increasing the loading strain rate. The strength of WZ is similar to that of BM, but its toughness is much lower than that of BM. The toughness of HAZ is the same as that of WZ, but its strength is much lower than that of BM and WZ. Based on the experimental results, an improved dynamic constitutive model was established to reasonably simulate the stress-strain curves of different regions from quasi-static loading to dynamic loading. Finite element (FE) analysis of transient rolling contact between rail welded joint and wheel under different conditions was performed. Compared with the results from quasi-static wheel-rail contact simulation, the equivalent plastic strain at each region of rail welded joint increases significantly and presents non-uniform distribution after considering the dynamic effect. When the wheel contacts the junction between different regions, the impact will cause a significant stress concentration at the rail welded joints. The maximum wheel-rail load by the implicit dynamic analysis is about 4 similar to 12 times that obtained by the quasi-static analysis. Moreover, the maximum contact pressure, equivalent stress and equivalent plastic strain of each area of rail welded joints gradually increase with the increase in axle load and driving speed.
查看更多>>摘要：In this paper, the fatigue behavior of resistance spot welding in the ferrite-martensite dual-phase steel joints with one and three spot-welds and hybrid joints have been investigated. Experimental parameters are welding time, electric current's intensity, and the compressive force applied. Design of experiments were done by Taguchi statistical method and because of the number of studied parameters and factors. In order to predict the optimal parameters of the resistance spot welding, signal to noise ratio is used in Taguchi method. Also, scanning electron microscope (SEM) images of the fracture surfaces of specimens are investigated to evaluate the effect of studied parameters from a morphological viewpoint. The results show that the effect of electric current on the fatigue life of joints is more than other parameters but its effectiveness diminishes as it increases. The adhesive on the hybrid joints also has a significant effect on the increase of its fatigue life and fatigue strength.
查看更多>>摘要：Stamping die is prone to wear failure due to mechanical friction. In this work, high-hardness boride layers were obtained on ductile cast iron as stamping die, by a boronizing process at 800-950 degrees C for 2-6 h with the addition of rare-earth oxide La2O3. A sawtooth-like morphology of the boride layer was observed using scanning electron microscopy (SEM). The greatest boride layer micro-hardness of the boride layers of 1648 HV0.1 was obtained at 900 degrees C and 6 h with 4% La2O3, and X-ray diffraction (XRD) analysis showed that the boride layers were a component of Fe2B as adding La2O3. The tribological tests showed that the wear resistance of the boride layers was enhanced with increasing boronizing temperature and time, where the ductile cast iron substrate corresponding to 900 degrees C and 6 h exhibited the best wear resistance. Compared with that of the boride layer without La2O3, the thickness and wear resistance of the boride layer with 4% La2O3 was increased by 37.2% and 31%, respectively. The thickness of the boride with 6% La2O3 decreased by 27.6%, and the wear rate was highest, indicating that excessive La2O3 inhibited the enhancement effect. The wear mechanism of the boride layers transformed from mild adhesive wear to fatigue spalling as the normal load and sliding speed increased.
查看更多>>摘要：The mechanical behavior of high-viscosity coal gangue paste (CGP) has been studied, while computational fluid dynamics and discrete element coupling method (DEM-CFD) was employed for it. Through the bidirectional coupling of particles and fluid, the force among different particles in the pipe and the effect of collisions were analyzed. The particle-pipe or particle-wall collision force has been solved by coupling the finite element method with discrete element method (DEMFEM). The mechanical analysis of pipe's life is realized, which was based on the fracture and fatigue analysis software NCODE, in which the actual pipe material parameters used in engineering were considered. The numerical simulation results show that the erosion of the flow field in the pipe (inlet and elbow) is serious, and the life of the parts will be greatly shortened. The simulation results agree with the results of field test very well. Hence, this numerical simulation method can be used to simulate the pipe erosion and wear, estimate the pipe's life, and predict the positions of the failure.
查看更多>>摘要：In this paper, the failure mechanisms of environmentally degraded hybrid glass/carbon fiber reinforced epoxy composites that are subjected to tensile loading are examined. The test specimens are manufactured by vacuum bag molding and the hybrid laminates are exposed to 5 wt% nitric acid at room temperature. The study is carried out by using a combination of Acoustic Emission (AE) nondestructive testing and scanning electron microscopy. Matrix cracking, matrixfiber debonding, and fiber failure are found to be the main causes of reduction of mechanical properties of the exposed specimens. Unlike the control sample, the exposed specimens show an additional group of acoustic emission events that could be correlated to a delamination between glass and carbon fiber layers. It can be concluded that the synergistic effect of the corrosive environment and stress induced by ion exchange phenomenon has led to fiber scission; which in turn has reduced the load-bearing capabilities of the composite specimens.
查看更多>>摘要：Bearing is the most precautious element in rotating machinery. Defects produced in any part of the bearing may lead to a hazardous environment that increases the noise and vibration. It can be diminished with appropriate loading combinations. The selection of optimum loading conditions requires developing an algorithm. Multiple Attribute Decision Making (MADM) techniques are utilized to pick up a unique and ideal solution or ranking of choices from the available alternatives. The MADM techniques have not been used for bearing fault diagnosis so far. This paper offers a novel methodology for the Ranking and Selection of Optimum Alternative based on Linear Scale Transformation (RSOA-LST), having combined benefit and cost criteria that rank the choices and determine the percentage influence of various alternatives. This methodology has been performed with several experimental signals of cylindrical roller bearing, acquired from twenty-four bearing conditions having several speeds and loading combinations. The normalization of attributes (statistical features) considering combined benefit-cost criteria, mean of various parameters (speeds, attributes, and bearing conditions), and Percentage Influencing (PI) are intended simultaneously to obtain the ranking of alternatives (loading conditions). Local Defect Analysis (LDA) and Global Defect Analysis (GDA) are carried out in this research. In LDA, the ranking of alternatives based on the PI for each defect and the ranking of bearings based on fluctuation in PI of various alternatives are attained. In GDA, the sequence of alternatives is obtained globally. The effectiveness of the suggested methodology has been verified over other MADM techniques. The outcomes state that the suggested technique effectively bifurcates the influence of alternatives locally as well as globally over other techniques.
Masoudi, AghdasJazi, Mohammad DavarpanahNejad, Reza MasoudiMohrekesh, Majid...
12页
查看更多>>摘要：The purpose of controlling and detecting errors in transportation systems is to ensure the correct operation of the system. The purpose of this paper is to identify wear in rails by using statistical pattern recognition methods. Due to the low accuracy of some of the current methods designing and introducing an easy way to be used in this area is required. The data of this paper were obtained by the field observation and using image captions of without worn profile and worn profile of railway rails, then the wear phenomenon was identified using the image processing method. Comparing the results of wear identification using pattern recognition techniques is in accordance with field observations. The true positive rate (sensitivity) is calculated and the accuracy of the proposed method indicates the validity of the proposed model.
NSTL
Elsevier