In the freight railway bridge, the increase of the train running speed and train axle loads can enlarge dynamic response (DR) of the railway bridges, which leads to excessive vibration of bridges and endangers the structural safety. In this paper, a three-dimensional coupled finite element (FE) model of a heavy-haul freight train-track-bridge (HHFTTB) is established using multibody dynamics theory and FE method, and the DR for the coupled system of HHFTTB are solved by ABAQUS/Explicit dynamic analysis method. The field-measured data for a 32 m simply supported prestressed concrete beam of a heavy-haul railway in China are analyzed, and the validity of the FE model is verified. Finally, the effects of train formation number, train running speed, and train axle loads on DR of the heavy-haul railway bridge structures are studied. The results show that increasing the train formation number only has an influence on DR duration of the bridge structure, rather than the peak value of DR, when the train formation number exceeds a certain number; besides, the train axle loads and train running speed have significant influence on DR of the bridge structure. The results of this study can be used as reference for the design of heavy-haul railway bridges and the reinforcement transformation of existing railway bridges.
The microstructure and tribological properties of space copper-based friction material fabricated by Powder Metallurgy technology were studied using optical metallographic microscope and MM-1000-type tribo-tester, respectively. The results are shown as follows: The lubricant MoS2 was resolved during sintering, resulting in the loss of S element. MoS2 and its resolvents reacted with other components into some new compounds which contribute to the tribological properties of friction material. The lubrication mechanism of these new compounds showed essential difference in comparison to that for MoS2; the friction coefficient was higher under atmospheric condition than that under vacuum conditions, but almost the same under low and high vacuum conditions. It decreased under both atmospheric and low vacuum conditions with the increase of load. The environmental temperature had insignificant effect on the friction coefficient; under atmospheric condition as load increased, the mass loss of material decreased linearly, then increased. With regard to low vacuum condition as load increased, the mass loss of material increased, then decreased; the stable coefficient of friction material under vacuum condition was higher than that under atmospheric condition.
The microstructures and tribological properties of materials for friction pairs used to space docking were investigated by optical metallographic microscope and a special home-made tribo-tester, respectively. The results demonstrate that friction material appears homogeneous and compact microstructure. Counterpart material presents temper sorbite which keeps martensite morphology and residues a small amount of blocky undissolved ferrite; the porosity of friction material is about 3.7%. Materials for space docking show favorable rigidity; during running-in, friction torque of friction pairs can be enhanced obviously; under different operation conditions, friction pairs for space docking possesses different friction coefficient.
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