ABSTRACT
To investigate the relationship between surface microstructure and wear mechanism in D2/U71Mn wheel-rail material under different contact stress conditions, rolling wear tests using a GPM-40 wear machine to simulate the wheel-rail operation was performed. After wear tests, an optical microscope (OM), scanning electron microscope (SEM) and micro-hardness testers were used to characterize the microstructure and fatigue wear cracks. The results show that the thickness of the plastic deformation layer and surface hardness is increased with the increase of contact stress. Under high contact stress condition (1200 MPa), the severe plastic deformation layer led to the formation of fatigue wear of wheel-rail samples. Under a contact stress of 700 MPa, the wear mechanism of samples is adhesive wear and wear rate is low. With the increase of contact stress, the fatigue cracks are gradually severe. Under a contact stress of 1200 MPa, the wear mechanism of samples becomes fatigue wear and the fatigue wear cracks cause the increase of wear rate. The fatigue wear can accelerate the wear failure of wheel-rail samples. The fatigue wear cracks of wheel samples are severer than that of rail samples due to both the rate of plastic strain and the content of proeutectoid ferrite.
ABSTRACT
By using wavelet transform and remote sensing techniques, the influence of climate change on the unique mosaic landscape of sand land-wetland in middle-east Inner Mongolia in 1961 -2005 was studied. The results showed that in 1961-2005, the annual air temperature in study area had an increment of 0.32 degrees C x (10 a)(-1), the annual precipitation fluctuated with a cycle of 30 years and of 15 years, and the annual average wind speed decreased by 0.26 m x s(-1) x (10 a)(-1). In the southeast part of study area, which located in the places between Hunshandake sand land and Keerqin Deserts, there was a district, in which, the climatic characteristics did not change evidently. Until 2010, the study area would still have an increasing air temperature, lesser precipitation, and decreasing wind speed. Under the influence of warming and drying, the total area of Hunshandake sand land and the wetland around reduced year after year, and, with the vegetation degradation on sand land, wetland shrunk and lake dried up, moving sand land enlarged ceaselessly, while immovable and semi-moving sand lands reduced obviously.
