查看更多>>摘要：An adaptive finite element method linked with user-defined subroutine UMESHMOTION is developed for simulating the tangential fretting wear of PVDF piezoelectric thin films. The three-dimensional (3D) sphere-onflat contact model is established for the fretting wear simulation by using commercial software ABAQUS, where the Si3N4 ceramic ball is used as the punch in contact with PVDF piezoelectric thin films. The variable friction coefficient obtained from experiments is taking into consideration. The calculation of wear is based on the Archard's wear model. The tangential fretting motion with different loads and variable friction coefficients are applied in the finite element simulation. The fretting wear test are carried out to verify the numerical results under the same conditions. The results indicate that the present adaptive finite element model has a certain accuracy comparable to the experiment results for the fretting wear of PVDF piezoelectric thin films.
查看更多>>摘要：Recently, field measurements show that corrugations are generated on curved tracks and that its wavelength varies with fasteners. The phenomenon that corrugations are generated on curved tracks can be explained with the assumption that corrugation is generated by the torsional vibration of wheelset. This assumption, however, has not been investigated in details yet. In this research, a finite element model including the nonlinear friction-creepage characteristics is developed to analyse the unstable vibration of a wheelset negotiating a curved track, and the results show that the friction induced torsional vibration between inner wheel and rail is most likely to be generated, which can verify the assumption. Furthermore, a mathematical model is developed to illustrate the forming process of rail corrugation, and the results indicate that the corrugation generated on curved track can be attributed to the periodical fluctuation of frictional power due to torsional vibration. Based on the results above, a forming process model of rail corrugation is formulated, which can be applied to explain why wave-length of corrugation varies with fasteners: the vertical dynamics affected by fasteners determine the frequency of torsional vibration and further affect the wavelength of corrugation, indicating the reliability and effectiveness of this forming process model.
查看更多>>摘要：Tribofilms and microcracks developed on a carburized SCM420 steel through a two-roller-type pitting test were characterized. Tribofilms composed mainly of calcium phosphate, iron phosphate, and iron oxide were generated on the contact surface. The tribofilms were homogeneously distributed on the contact surfaces that exhibited a longer life, suggesting that the tribofilm distribution affects the rolling sliding contact fatigue (RCF) life. Compounds including the elements from the lubricant were also generated on the surfaces of microcracks formed on the contact surface, suggesting that lubricant flowed into the surface microcracks during the test. The martensitic microstructure at the specimen subsurface was dynamically reconstructed to an ultrafine-grained microstructure during RCF, which resulted in the residual stress relief, especially on the contact surface. After the residual stress release, the fluid pressurization accelerated the formation of a mixed-mode microcrack of mode I and mode II with a high angle to the surface in the later stage, while a shallow microcrack in mode II developed during the early stage.
查看更多>>摘要：With the increasing concern of vehicle safety, higher requirements are put forward for the stability of friction performance of brake linings and clutch surface materials. This work introduces a feasible method to prepare boron phenolic resin (BPR) matrix friction composites with improved heat fade resistance by using recycled polyimide (PI) powders as tribological modifier fillers. The friction and wear behavior of the BPR matrix composites during dry sliding with GCr15 at 100 degrees C, a heating process of 100-350 degrees C, and a temperature of 350 degrees C were investigated. Experimental results showed that recycled PI powders could improve the stability of friction coefficient at high temperatures and reduce the heat fade rate of composites since PI powders could effectively reduce the generation of friction debris under high temperatures peeling. SEM showed that the PI powders could be well embedded in the matrix, and they were tightly and continuously bonded. The wear rate of modified composites was reduced by 61.1% at 350 degrees C, mainly due to the formation of a lubricating film on the contact surfaces, which protected the polymer matrix from severe wear during sliding. When the PI powders content was 10 wt%, the heat fade rate was only about 4.69% for enlarging the applications in the brake linings.
NSTL
Elsevier