石灰改良膨胀土的基本特性

根据蚌明高速公路工程实例,就弱膨胀土石灰改良后路用基本性质进行室内试验研究,研究结果对工程实践具有一定的应用价值。

合肥北绕城高速公路石灰改良膨胀土的试验研究

膨胀土是一种吸水膨胀、失水收缩、胀缩变形显著的粘性土,其主要工程性质对公路有比较强的破坏作用,要减少膨胀土对路基路面的破坏,必须从设计上采取措施加以处理。

Variation in Grain Size Distribution in Debris Flow

Grain composition of debris flow varies considerably from fluid to deposit, making it uncertain to estimate flow properties （e.g., density, velocity and discharge） using deposit as done in practice. Tracing the variation of grain composition is thus more important than estimating some certain properties of flow because every debris flow event consists of a series of surges that are distinct in properties and flow regimes. We find that the materials of debris flows, both the fluid and the source soils, satisfy a universal grain size distribution （GSD） in a form of P （D） = CD-zexp（-D/Dc）, where the parameters C, p and De are determined by fitting the function to the grain size frequency. A small At implies a small porosity and possible high excess pore pressure in flow; and a large D~ means a wide range of grain composition and hence a high sediment concentration. Flow density increases as 11 decreases or Dc increases, in a power law form. A debris flow always achieves a state of certain mobility and density that can be well described by the coupling of p and Dc, which imposes a constraint on the fluctuations of flow surges. The GSD also describes the changes in grain composition in that it is always satisfied during the course of debris flow developing. Numerical simulation using the GSD can well illustrate the variation ofμ and Dc from source soils to deposits.

Comparison of microstructure and wear resistance of A356-SiC_p composites processed via compocasting and vibrating cooling slope

The influences of SiC content on the microstructure, porosity, hardness and wear resistance of A356？SiCp composites processed via two different methods of compocasting and vibrating cooling slope （VCS） were compared with each other. In the as-cast condition, the matrix of VCS and compocast processed composites exhibited globular and dendritric structures, respectively. While a more uniform distribution of SiC particulates in the matrix alloy as well as higher hardness values were obtained for the VCS processed samples, the composites produced via compocasting exhibited less porosity. The increased SiC content （up to 20% in volume fraction） resulted in a more uniform distribution of SiC particles within the matrix alloy and improved wear resistance for both the composite series. However, for the VCS processed composites, the increased SiC content, resulted in the decreased size and shape factor of globules as well as better tribological properties when compared with compocast composites. It was concluded that the improved properties of the VCS processed composites when compared with their compocast counterparts was a consequence of a more uniform distribution of SiC particulates in the matrix alloy as well as the globular microstructure generated during the VCS process.

Numerical simulation of powder effect on solidification in directed energy deposition additive manufacturing

An integrated simulation of powder effects on particle temperature and microstructural evolution in laser directed energy deposition additive manufacturing process was carried out.The spatial distribution of the flying powder particles was simulated by the discrete element method to calculate the energy for the flying powder particles under the laser−particle interaction with electromagnetic wave analysis.Combined with the phase field method,the influence of particle size on the microstructural evolution was studied.The microstructural evolution is validated through comparison with experimental observation.Results indicate that the narrow particle size distribution is beneficial to obtaining a more uniform temperature distribution on the deposited layers and forming smaller equiaxed grains near the side surfaces of the sample.Appropriate powder particle size is beneficial to the conversion of the electromagnetic energy into heat.Particles with small size are recommended to form equiaxed grains and to improve product quality.Appropriate powder flow rate improves the laser energy efficiency,and higher powder flow rate leads to more uniform equiaxed grains on both sides of the cross-section.

Origin of Quaternary Red Clay of Southern Anhui Province

The particle size distribution, heavy mineral constituents and rare earth elements (REE) characteristics of the Quaternary red clay of southern Anhui Province were studied to explore the origin of the clay. The results showed that the clay had some properties of areolian deposits, which could be compared with those of the loess in North China; and its chondrite normalized curves of REE were similar to those of the Xiashu loess, implying that they shared the same origin. It was concluded in combination with the results reported by other researchers that the Quaternary red clay of southern Anhui Province originated from aeolian deposits, and this could reveal the cycles of warm and cold climates in the area during the Quaternary period.

Preparation of Nano-sized Silica-alumina Support by Supersolubilizing Self-assembly Technique

Nano-sized silica-alumina particles were in-situ synthesized in supersolubilizing reverse micellae.Both the most probable pore diameters and the particle sizes were distributed in nano-scale SiO2-Al2O3 particulates.The influence of SiO2/Al2O3 mass ratio and the surfactant content on the particle size and morphology,pore structure,and acidity was characterized by the low temperature nitrogen adsorption/desorption (BET),SEM,TEM and NH3-TPD methods.The test results indicated that the most probable pore diameter of SiO2-Al2O3 nanoparticles was around 10 nm,the specific surface area was about 223-286 m2 /g,the pore volumes were about 0.48-0.63 cm 3 /g,and the particle sizes of porous SiO2-Al2O3 calcined at 550 ℃ were distributed always in the range between 10 nm to 50 nm.The calcined SiO2-Al2O3 nano-powders showed their acidity being stronger than the porous γ-Al2O3 support.

Numerical partitioning of components for four-modal sedimentary grain-size distribution based on gradient descent method

The gradient descent(GD)method is used to fit the measured data(i.e.,the laser grain-size distribution of the sediments)with a sum of four weighted lognormal functions.The method is calibrated by a series of ideal numerical experiments.The numerical results indicate that the GD method not only is easy to operate but also could effectively optimize the parameters of the fitting function with the error decreasing steadily.The method is applied to numerical partitioning of laser grain-size components of a series of Garzêloess samples and three bottom sedimentary samples of submarine turbidity currents modeled in an open channel laboratory flume.The overall fitting results are satisfactory.As a new approach of data fitting,the GD method could also be adapted to solve other optimization problems.

High frequency properties of Fe_(73.5)Cu_1Nb_3Si_(13.5)B_9/Zn_(0.5)Ni_(0.5)Fe_2O_4 soft magnetic composite with micro-cellular structure

Soft magnetic composite with micro-cellular structure was prepared by spark plasma sintering(SPS) process with Fe73.5Cu1Nb3Si13.5B9 micron-powders clad by 5wt% Zn0.5Ni0.5Fe2O4 nano-particles.The effect of SPS on the micro structure of the Finemet powder and the micro structure of the composite were studied.It has been found that the as-prepared composite consists of Fe73.5Cu1Nb3Si13.5B9 cells and the cell-wall composed of nano Zn0.5Ni0.5Fe2O4 particles distributing around Fe73.5Cu1Nb3Si13.5B9 cell-body.The composite exhibits low eddy-current loss which is to be resulted by high resistivity of the Zn0.5Ni0.5Fe2O4 cell-wall.The sintered samples were annealed at different temperature and the magnetic properties at different frequency of the annealed samples were measured.It shows that the Zn0.5Ni0.5Fe2O4 cell-wall possesses good thermostability.