一种新型陶瓷材料及其耐磨性

对新型Ａｌ２Ｏ３－ＴｉＣ－Ｃｏ陶瓷的磨粒磨损，冲蚀磨损及其在单颗粒作用下的摩擦磨损行为进行了研究。与ＡＴ３０（７０ｗｔ％Ａｌ２Ｏ３－３０ｗｔ％ＴｉＣ）陶瓷相比，Ａｌ２Ｏ３－ＴｉＣ－Ｃｏ陶瓷具有更为良好的耐磨性，金属钴的存在提高了基体的韧性，细化了晶粒，其综合力学性能得到了显著提高，ＡＴＣ陶瓷样品耐磨性与其强韧化水平和细致的组织结构有关。     

Identification of critical erosion prone areas in the small agricultural watershed using USLE,GIS and remote sensing

In the present study, Karso watershed of Hazaribagh, Jharkhand State, India was divided into 200 × 200 grid cells and average annual sediment yields were estimated for each grid cell of the watershed to identify the critical erosion prone areas of watershed for prioritization purpose. Average annual sediment yield data on grid basis was estimated using Universal Soil Loss Equation (USLE). In general, a major limitation in the use of hydrological models has been their inability to handle the large amounts of input data that describe the heterogeneity of the natural system. Remote sensing (RS) technology provides the vital spatial and temporal information on some of these parameters. A recent and emerging technology represented by Geographic Information System (GIS) was used as the tool to generate, manipulate and spatially organize disparate data for sediment yield modeling. Thus, the Arc Info 7.2 GIS software and RS (ERDAS IMAGINE 8.4 image processing software) provided spatial input data to the erosion model, while the USLE was used to predict the spatial distribution of the sediment yield on grid basis. The deviation of estimated sediment yield from the observed values in the range of 1.37 to 13.85 percent indicates accurate estimation of sediment yield from the watershed.     

Uncertainty of Predictions of Embankment Dam Breach Parameters

Risk assessment studies considering the failure of embankment dams often require the prediction of basic geometric and temporal parameters of a breach, or the estimation of peak breach outflows. Many of the relations most commonly used to make these predictions were developed from statistical analyses of data collected from historic dam failures. The prediction uncertainties of these methods are widely recognized to be very large, but have never been specifically quantified. This paper presents an analysis of the uncertainty of many of these breach parameter and peak flow prediction methods. Application of the methods and the uncertainty analysis are illustrated through a case study of a risk assessment recently performed by the Bureau of Reclamation for a large embankment dam in North Dakota.     

含微量元素铜焊锡丝的研制

在６０／４０的锡铅焊料中加入０．２％左右的铜，凝固后具有均匀细小的共晶组织，其熔点为１８３℃，焊点强度和扩展率均高于未加铜的６０／４０锡铅焊料，并且含铜的锡铅焊料在焊接时，对铜烙铁头和微细铜线了小的熔蚀性。     

Erosion rate correlations of a pipe protruded in an abrupt pipe contraction

Erosion is one of the most serious problems in various gas and liquid flow passages such as flow in pipes, pumps, turbines, compressors and many other devices. Sand presence causes loss of pipe wall thickness that can lead to pipe erosion, frequent failures and loss of expensive production time. The importance of this problem is mainly due to many related engineering applications, viz. heat exchangers. In order to reduce the frequency of such pipe erosions, caps in the form of replaceable pipes are protruded in the sudden contraction regions which are exposed to most of the serious erosion rates. In the present work, numerical investigation of the erosion of a pipe protruded in a sudden contraction is presented. The turbulent, steady, 2-D axi-symmetric flow inside an axi-symmetric abrupt contraction pipe with a pipe protrusion embedded in it was solved by steady-state time averaged conservation equations of mass and momentum along with two equation model for turbulence. Particles are tracked using Lagrangian particle tracking. An erosion model was employed to investigate the erosion phenomena for the given geometry. The influence of the different parameters such as the inlet flow velocity (3–10 m/s), the particle diameter (10–400 μm), the protruded pipe geometry (thickness T=1–5 mm and depth H=2–5 mm) and the pipe contraction ratio (Cr=0.25–0.5) on the erosion of pipe protrusion was investigated. Correlations for the influence of inlet flow velocity, depth and thickness of the protruded pipe on the erosion rate are presented.     

Erosion, corrosion and erosion–corrosion of EB PVD thermal barrier coatings

Electron beam (EB) physical vapour deposited (PVD) thermal barrier coatings (TBCs) have been used in gas turbine engines for a number of years. The primary mode of failure is attributed to oxidation of the bond coat and growth of the thermally grown oxide (TGO), the alumina scale that forms on the bond coat and to which the ceramic top coat adheres. Once the TGO reaches a critical thickness, the TBC tends to spall and expose the underlying substrate to the hot gases. Erosion is commonly accepted as a secondary failure mechanism, which thins the TBC thus reducing its insulation capability and increasing the TGO growth rate. In severe conditions, erosion can completely remove the TBC over time, again resulting in the exposure of the substrate, typically Ni-based superalloys. Since engine efficiency is related to turbine entry temperature (TET), there is a constant driving force to increase this temperature. With this drive for higher TETs comes corrosion problems for the yttria stabilised zirconia (YSZ) ceramic topcoat. YSZ is susceptible to attack from molten calcium–magnesium–alumina–silicates (CMAS) which degrades the YSZ both chemically and micro-structurally. CMAS has a melting point of around 1240 °C and since it is common in atmospheric dust it is easily deposited onto gas turbine blades. If the CMAS then melts and penetrates into the ceramic, the life of the TBC can be significantly reduced. This paper discusses the various failure mechanisms associated with the erosion, corrosion and erosion–corrosion of EB PVD TBCs. The concept of a dimensionless ratio D/d, where D is the contact footprint diameter and d is the column diameter, as a means of determining the erosion mechanism is introduced and discussed for EB PVD TBCs.     

Effect of Floodwater Extraction on Mountain Stream Morphology

Floodwater is often extracted for consumptive purposes from western mountain streams in the United States. The long-term extraction of floodwater may alter the morphological and ecological balance of such streams. Scale model experiments based on eight mountain gravel-bed streams in Idaho were conducted to test the effects of floodwater extraction on stream morphology. The model channel transported a poorly sorted mix of model “gravel,” as well as copious amounts of model “sand.” The channel had a discontinuous floodplain, developed its own bar morphology, and contained large model colluvium as well as a bedrock platform. A mobile-bed equilibrium was first developed using a repeated hydrograph. The experiment was then repeated using a sliding cutoff discharge. The discharges in the hydrograph that were below a given cutoff discharge were reduced to 30% of bankfull discharge. By raising the cutoff discharge, it was possible to study the effect of increasing severity of floodwater extraction on stream morphology. The experiments indicated an increase in sand content on the bed surface and a decrease in the standard deviation of fluctuations in bed elevation with increasing severity of floodwater extraction.     

Digital Yellow River Model

Soil erosion is one of the key concerns in land use management for the Loess Plateau of the Yellow River, where serious soil loss is the root cause of environmental and ecological degradation of the basin. In this paper, a physically-based, distributed-parameter, and continuous erosion prediction model at the river basin scale was developed with the aim of assisting in developing better land use management strategies. The framework, the major supporting techniques, and the typical erosion processes are described. The physical processes of sediment yield and transport in the Loess Plateau are divided into three sub-processes, including the runoff and sediment yield on hillslopes, gravitational erosion in gullies, and hyperconcentrated flow routing in channels. For each sub-process, a physically-based simulation model was developed and embedded into the whole model system. The model system was applied to simulate the runoff and sediment yield in several typical years in the coarse sediment source area of the Loess Plateau, and the simulated results were in reasonably good agreement with the measured values.     

TTI hydraulics and erosion control laboratory research field performance of erosion-control blankets

Storm water management issues facing the Texas Department of Transportation in the late 1980s led to the development of a coordinated research program with the Texas Transportation Institute. Researchers developed methodologies for evaluating the field performance of various erosion control technologies of the most widely used products within the Department's construction and maintenance operations. From these methodologies, the Hydraulics and Erosion Control Laboratory was designed and constructed. Currently, participants include private industry (manufacturers of erosion control products), transportation researchers (TTI), and the public sector (TxDOT).The results reported in this paper reflect 2 years of erosion-control blanket research. The study objectives were to determine the effectiveness of erosion-control blankets on the growth of warm-season perennial grasses and their ability to prevent sediment loss in a sloped condition.The laboratory simulates the highway environment with the sloped plots (6 m in width) located on an earthen embankment that is 300 m in length and 6.75 m in height (94 ft. by 22 ft., vertically). A randomized experimental design was replicated on two soil types (sand and clay) for each slope condition (3:1 or 2:1) with a control.In general, the results indicate better combined results relating to sediment retention and vegetation establishment performance for erosion-control blankets on sandy soils (noncohesive) regardless of slope condition (3:1 or 2:1) or material type. A minimum of 50% more sediment was retained on the sandy treatment plots and a 45% more vegetation coverage was achieved compared with the control plots. When analyzed by material type related to performance, excelsior, synthetic blends, and straw/coconut blends performed the best. For clay soils (cohesive), regardless of slope condition (3:1 or 2:1), the combined results indicate a minimum of 75% more sediment was retained and a minimum of 5% more vegetation establishment was achieved compared with the control plots. When analyzed by material type related to performance, excelsior, straw, and straw/coconut blends performed the best.