Mechanism Analysis of Landslide of a Layered Slope Induced by Drawdown of Water Level

The frequent drawdown of water level of Yangtze River will greatly influence the stability of the widely existing slopes in the Three Gorges reservoir zone, especially those layered ones. Apart from the fluctuating speed of water level, the different geological materials will also play important roles in the failure of slopes. Thus, it must be first to study the mechanism of such a landslide caused by drawdown of water level.A new experimental setup is designed to study the performance of a layered slope under the drawdown of water level. The pattern of landslide of a layered slope induced by drawdown of water level has been explored by means of simulating experiments. The influence of fluctuating speed of water level on the stability of the layered slope is probed,especially the whole process of deformation and development of landslide of the slope versus time. The experimental results show that the slope is stable during the water level rising, and the sliding body occurs in the upper layer of the slope under a certain drawdown speed of water level. In the process of slope failure, some new small sliding body will develop on the main sliding body, and the result is that they speed up the disassembly of the whole slope.Based on the simulating experiment on landslide of a layered slope induced by drawdown of water level, the stress and displacement field of the slope are calculated.The seepage velocity, the pore water pressure, and the gradient of pore water head are also calculated for the whole process of drawdown of water level. The computing results are in good agreement with the experimental results. Accordingly, the mechanism of deformation and landslide of the layered slope induced by drawdown of water level is analyzed. It may provide basis for treating this kind of layered slopes in practical engineering.

Temperature Dependence of the Tribological Properties of Laser Re-Melted Al-Cu-Fe Quasicrystalline Plasma Sprayed Coatings

The aim of this study was to investigate the effect of temperature on tribological properties of plasma-sprayed Al-Cu-Fe quasicrystal (QC) coating after laser re-melting treatment. The laser treatment resulted in a more uniform, denser and harder microstructure than that of the as-sprayed coatings. Tribological experiments on the coatings were conducted under reciprocating motion at high frequency in the temperature range from 25 to 650 degreesC. Remarkable influence of temperature on the friction behavior of the coating was recorded and analyzed. Microstructural analysis indicated that the wear mechanisms of the re-melted QC coatings changed from abrasive wear at room temperature, to adhesive wear at 400 degreesC and severe adhesive wear at 650 degreesC owing to the material transfer of the counterpart ball. It was also observed that the ratio of the icosahedral (i)-phase to beta-Al-50(Fe,CU)(50) phase in the coating was higher after test at 400 'C than that at 650 'C. The variation of the ratio UP of coating and of the property of the counterpart ball and coating with the temperature are the two main factors influencing the wear mechanisms and value of the friction coefficient.

Microstructure Study Of Laser Welding Cast Nickel-Based Superalloy K418

Experiments of laser welding cast nickel-based superalloy K418 were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness. The corresponding mechanisms were discussed in detail. Results show that the laser welded seam have non-equilibrium solidified microstructures consisting of Cr-Ni-Fe-C austenite solid solution dendrites as the dominant and some fine and dispersed Ni-3(Al,Ti) gamma' phase as well as little amount of MC needle carbides and particles enriched in Nb, Ti and Mo distributed in the interdendritic regions, cracks originated from the liquation of the low melting points eutectics in the HAZ grain boundary are observed, the average microhardness of the welded seam and HAZ is higher than that of the base metal due to alloy elements' redistribution of the strengthening phase gamma'. (C) 2008 Elsevier B.V. All rights reserved.

Research on laser welding of cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft

Exploratory experiments of laser welding cast Ni-based superalloy K418 turbo disk and alloy steel 42CrMo shaft were conducted. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. The corresponding mechanisms were discussed in detail. Results showed that the laser-welded seam had non-equilibrium solidified microstructures consisting of FeCr0.29Ni0.16C0.06 austenite solid solution dendrites as the dominant and some fine and dispersed Ni3Al gamma' phase and Laves particles as well as little amount of MC short stick or particle-like carbides distributed in the interdendritic regions. The average microhardness of the welded seam was relatively uniform and lower than that of the base metal due to partial dissolution and suppression of the strengthening phase gamma' to some extent. About 88.5% tensile strength of the base metal was achieved in the welded joint because of a non-full penetration welding and the fracture mechanism was a mixture of ductility and brittleness. The existence of some Laves particles in the welded seam also facilitated the initiation and propagation of the microcracks and microvoids and hence, the detrimental effects of the tensile strength of the welded joint. The present results stimulate further investigation on this field. (c) 2006 Elsevier B.V. All rights reserved.

Experimental Study Of Vortex-Induced Vibrations Of A Pipeline Near An Erodible Sandy Seabed

Based on similarity analyses, a series of experiments have been conducted with a newly established hydro-elastic facility to investigate the transverse vortex-induced vibrations (VIVs) of a submarine pipeline near an erodible sandy seabed under the influence of ocean currents. Typical characteristics of coupling processes between pipe vibration and soil scour in the currents have been summarized for Case 1: pipe is laid above seabed and Case 11: pipe is partially embedded in seabed on the basis of the experimental observations. Pipe vibration and the corresponding local scour are usually two coupled physical processes leading to an equilibrium state. The influence of initial gap-to-diameter ratio (e(0)/D) on the interaction between pipe vibration and local scour has been studied. Experimental results show that the critical values of V-r for the initiation of VIVs of the pipe near an erodible sand bed get bigger with decreasing initial gap-to-diameter ratio within the examined range of e(0)/D (-0.25 < e(0)/D < 0.75). The comparison of the pipe vibrations near an erodible soil with those near a rigid boundary and under wall-free conditions indicates that the vibration amplitudes of the pipe near an erodible sand bed are close to the curve fit under wall-free conditions; nevertheless, for the same stability parameter, the maximum amplitudes for the VIV coupled with local scour increase with the increase of initial gap-to-diameter ratio. (c) 2007 Elsevier Ltd. All rights reserved.

Effects of Mach number on turbulent separation behaviours induced by blunt fin

An experimental study of the interaction between shock wave and turbulent boundary layer induced by blunt fin has been carried out at M-infinity = 7.8 using oil flow visualization and simultaneous measurements of fluctuating wall pressure and heat transfer. This paper presents the effects of Mach number on turbulent separation behaviours induced by blunt fin.

An experimental study for wave-induced instability of pipelines: the breakout of pipelines

In this paper, a series of experiments have been conducted in a U-shaped oscillatory flow tunnel, which provides a more realistic simulation than the previous actuator loading methods. Based on the experimental data of pipe displacement with two different constraint conditions (freely laid pipelines and anti-rolling pipelines), three characteristic times in the process of pipeline losing stability are identified. The effects of sand size on the pipeline lateral stability are examined for freely laid pipelines. The empirical relationships between non-dimensional pipeline weight (G) and Fronde number (Fr-b) are established for different constraint conditions, which will provide a guide for engineering practice. (C) 2002 Elsevier Science Ltd. All rights reserved.

Surface-induced melting of metal nanoclusters

We investigate the size effect on melting of metal nanoclusters by molecular dynamics simulation and thermo dynamic theory based on Kofman's melt model. By the minimization of the free energy of metal nanoclusters with respect to the thickness of the surface liquid layer, it has been found that the nanoclusters of the same metal have the same premelting temperature T-pre = T-0 - T-0(gamma(su) - gamma(lv) - gamma(sl))/(rhoLxi) (T-0 is the melting point of bulk metal, gamma(sv) the solid-vapour interfacial free energy, gamma(sl) the liquid-vapour interfacial free energy, gamma(sl),l the solid-liquid interfacial free energy, p the density of metal, L the latent heat of bulk metal, and xi the characteristic length of surface-interface interaction) to be independent of the size of nanoclusters, so that the characteristic length of a metal can be obtained easily by T-pre, which can be obtained by experiments or molecular dynamics (MD) simulations. The premelting temperature T-pre of Cu is obtained by AID simulations, then xi is obtained. The melting point T-cm is further predicted by free energy analysis and is in good agreement with the result of our MD simulations. We also predict the maximum premelting-liquid width of Cu nanoclusters with various sizes and the critical size, below which there is no premelting.

Dissimilar autogenous full penetration welding of superalloy K418 and 42CrMo steel by a high power CWNd : YAG laser

Experiments of autogenous laser full penetration welding between dissimilar cast Ni-based superalloy K418 and alloy steel 42CrMo flat plates with 3.5 mm thickness were conducted using a 3 kW continuous wave (CW) Nd:YAG laser. The influences of laser welding velocity, flow rate of side-blow shielding gas, defocusing distance were investigated. Microstructure of the welded seam was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Mechanical properties of the welded seam were evaluated by microhardness and tensile strength testing. Results show that high quality full penetration laser-welded joint can be obtained by optimizing the welding velocity, flow rate of shielding gas and defocusing distance. The laser-welded seam have non-equilibrium solidified microstructures consisting of gamma-FeCr0.29Ni0.16C0.06 austenite solid solution dendrites as the dominant and very small amount of super-fine dispersed Ni3Al gamma' phase and Laves particles as well as MC needle-like carbides distributed in the interdendritic regions. Although the microhardness of the laser-welded seam was lower than that of the base metal, the strength of the joint was equal to that of the base metal and the fracture mechanism showed fine ductility. (c) 2007 Elsevier B.V. All rights reserved.

Embryo-damage induced nucleation of microcracks in an aluminum-alloy under impact loading

The nucleation of microdamage under dynamic loading was investigated through planar impact experiments accomplished with a light gas gun. The microscopic observation of recovered and sectioned specimens showed that microcracks were nucleated only by cracking of brittle particles inside material. However, for comparison the in situ static tensile tests on the same material conducted with a scanning electron microscope showed that the microcracks were nucleated by many forms those were fracture of ductile matrix, debonding particles from matrix and cracking of brittle particles. The quantitative metallographic observations of the specimens subjected to impact loading showed that most of the cracked particles were situated on grain boundaries of the aluminium matrix. These facts suggested the concept of critical size and incubation time of submicroscopic cavities in the dynamic case and the mechanism of embryo-damage induced nucleation by fracture of brittle particles in the aluminium alloy under impact loading was proposed.

Numerical simulation of evolution-induced catastrophe

A numerical simulation of damage evolution in a two-dimensional system of micocracks is presented. It reveals that the failure is induced by a cascade of coalescences of microcracks, and the fracture surface appears fractal. A model of evolution-induced catastrophe is introduced. The fractal dimension is found to be a function of evolution rule only. This result could qualitatively explain the correlation of fractal dimension and fracture toughness discovered in experiments.

Path Planner for Intelligent Laser Surface Modification

An optimal algorithm of manufacturing path planner for intelligent laser surface modification is presented. Elements included in the optimal objective have been analyzed. A 6-D manufacture trace that satisfies the requirements of special craft and 5-axis laser processing robot system has been generated from the path planner by method of parallel section in which combinations of modification spots size with curvature of processing surfaces and modification craft parameters are considered. Related experiments have been successfully carried out with the computer integrated multifunctional laser manufacturing system.

Numerical Simulation of Pulsed Laser Transformation Hardening

A novel pulsed laser surface processing technology is introduced, which can make use of the spatial and temporal profile of laser pulse to obtain ideal hardening parameters. The intensity distribution of laser pulse is spatially and temporally controlled by using laser shape transformation technology. A 3D numerical model including multi-phase transformations is established to explore material microstructure evolution induced by temperature field evolution. The influences of laser spatial-temporal profiles on hardening parameters are investigated. Different from the continuous laser processing technology, results indicate that spatial and temporal profiles are important factors in determining processing quality during pulsed laser processing method.

Nonlinear Fluid Damping In Structure-Wake Oscillators In Modeling Vortex-Induced Vibrations

A Nonlinear Fluid Damping (NFD) in the form of the square-velocity is applied in the response analysis of Vortex-induced Vibrations (VIV). Its nonlinear hydrodynamic effects oil the coupled wake and structure oscillators are investigated. A comparison between the coupled systems with the linear and nonlinear fluid dampings and experiments shows that the NFD model can well describe response characteristics, such as the amplification of body displacement at lock-in and frequency lock-ill, both at high and low mass ratios. Particularly, the predicted peak amplitude of the body in the Griffin plot is ill good agreement with experimental data and empirical equation, indicating the significant effect of the NFD on the structure motion.

Mechanisms in fs-laser ablation in fused silica

A theoretical model is proposed to describe the microscopic processes involved in the ablation in fused silica induced by femtosecond-laser pulse. Conduction-band electron (CBE) can absorb laser energy, the rate is calculated by quantum mechanical method and classical method. CBE is produced via photoionization (PI) and impact ionization (II). The PI and II rates are calculated by using the Keldysh theory and double-flux model, respectively. Besides the CBE production, we investigate laser energy deposition and its distribution. The equation of energy diffusion in physical space is resolved numerically. Taking energy density E-dep=54 kJ/cm(3) as the criterion, we calculate damage threshold, ablation depth, and ablation volumes. It is found that if energy diffusion is considered, energy density near sample surface is reduced to 1/10, damage threshold is enhanced more than 30%, ablation depth is increased by a factor of 10. Our theoretical results agree well with experimental measurements. Several ultrafast phenomena in fused silica are also discussed. (C) 2004 American Institute of Physics.