In debris flow modelling,the viscosity and yield stress of fine-grained sediments should be determined in order to better characterize sediment flow.In particular,it is important to understand the effect of grain size...In debris flow modelling,the viscosity and yield stress of fine-grained sediments should be determined in order to better characterize sediment flow.In particular,it is important to understand the effect of grain size on the rheology of fine-grained sediments associated with yielding.When looking at the relationship between shear stress and shear rate before yielding,a high-viscosity zone(called pseudoNewtonian viscosity) towards the apparent yield stress exists.After yielding,plastic viscosity(called Bingham viscosity) governs the flow.To examine the effect of grain size on the rheological characteristics of fine-grained sediments,clay-rich materials(from the Adriatic Sea,Italy; Cambridge Fjord,Canada; and the Mediterranean Sea,Spain),silt-rich debris flow materials(from La Valette,France) and silt-rich materials(iron tailings from Canada) were compared.Rheological characteristics were examined using a modified Bingham model.The materials examined,including the Canadian inorganic and sensitive clays,exhibit typical shear thinning behavior and strong thixotropy.In the relationships between the liquidity index and rheological values(viscosity and apparent yield stress),the effect of grain size on viscosity and yield stress is significant at a given liquidity index.The viscosity and yield stress of debris flow materials are higher than those of low-activity clays at the same liquid state.However the viscosity and yield stress of the tailings,which are mainly composed of silt-sized particles,are slightly lower than those of low-activity clays.展开更多
Fine-grained ZK60 magnesium alloy sheets of 2.0 mm in thickness were successfully joined by laser beam welding （LBW）. The effects of welding parameters including laser power and welding speed on the microstructures ...Fine-grained ZK60 magnesium alloy sheets of 2.0 mm in thickness were successfully joined by laser beam welding （LBW）. The effects of welding parameters including laser power and welding speed on the microstructures and mechanical properties of the joints were investigated. A sound bead, with the ultimate tensile strength （UTS） of 300 MPa and elongation of 12.0%, up to 92.5% and 65% of those of the base metal, respectively, is obtained with the optimized welding parameters. No liquation cracking is visible in the partially melted zone （PMZ） owing to the inhibitory action of the fine dispersed precipitates and the fine-grained microstructure in the as-rolled magnesium alloy sheets. The fusion zone （FZ） is featured with the equiaxed dendritic grains of the average grain size about 8 μm, which are similar to those in the heat affected zone （HAZ）, and this contributes to the relatively high joint efficiency.展开更多
The temperature field and thermal cycling curve in the heat-affected zone during welding 400 MPa ultra fine grained steel by plasma arc were simulated using finite element method. The principle of grain growth kinetic...The temperature field and thermal cycling curve in the heat-affected zone during welding 400 MPa ultra fine grained steel by plasma arc were simulated using finite element method. The principle of grain growth kinetics was used to predict the grain size in the heat-affected zone under different welding parameters. The simulation results show that the growing tendency of HAZ grain could be controlled by adjusting the welding parameters, but the growth of HAZ grain could not be eliminated at all. The HAZ grain size became small with increasing of the cooling rate and added with increasing of welding current, arc voltage and welding speed.展开更多
基金funded by the Natural Sciences and Engineering Research Council,Canada,via the COSTA(Continental Slope Stability)-Canada projectsupported by the Public Welfare & Safety Research Program through the National Research Foundation of Korea(NRF)+1 种基金funded by the Ministry of Science,ICT&Future Planning(Grant No.2012M3A2A1050983)the Research Project (11-7622,13-3212)of the Korea Institute of Geoscience and Mineral Resources(KIGAM)
文摘In debris flow modelling,the viscosity and yield stress of fine-grained sediments should be determined in order to better characterize sediment flow.In particular,it is important to understand the effect of grain size on the rheology of fine-grained sediments associated with yielding.When looking at the relationship between shear stress and shear rate before yielding,a high-viscosity zone(called pseudoNewtonian viscosity) towards the apparent yield stress exists.After yielding,plastic viscosity(called Bingham viscosity) governs the flow.To examine the effect of grain size on the rheological characteristics of fine-grained sediments,clay-rich materials(from the Adriatic Sea,Italy; Cambridge Fjord,Canada; and the Mediterranean Sea,Spain),silt-rich debris flow materials(from La Valette,France) and silt-rich materials(iron tailings from Canada) were compared.Rheological characteristics were examined using a modified Bingham model.The materials examined,including the Canadian inorganic and sensitive clays,exhibit typical shear thinning behavior and strong thixotropy.In the relationships between the liquidity index and rheological values(viscosity and apparent yield stress),the effect of grain size on viscosity and yield stress is significant at a given liquidity index.The viscosity and yield stress of debris flow materials are higher than those of low-activity clays at the same liquid state.However the viscosity and yield stress of the tailings,which are mainly composed of silt-sized particles,are slightly lower than those of low-activity clays.
基金Project(51274092)supported by the National Natural Science Foundation of ChinaProject(20120161110040)supported by the Doctoral Program of Higher Education of China
文摘Fine-grained ZK60 magnesium alloy sheets of 2.0 mm in thickness were successfully joined by laser beam welding （LBW）. The effects of welding parameters including laser power and welding speed on the microstructures and mechanical properties of the joints were investigated. A sound bead, with the ultimate tensile strength （UTS） of 300 MPa and elongation of 12.0%, up to 92.5% and 65% of those of the base metal, respectively, is obtained with the optimized welding parameters. No liquation cracking is visible in the partially melted zone （PMZ） owing to the inhibitory action of the fine dispersed precipitates and the fine-grained microstructure in the as-rolled magnesium alloy sheets. The fusion zone （FZ） is featured with the equiaxed dendritic grains of the average grain size about 8 μm, which are similar to those in the heat affected zone （HAZ）, and this contributes to the relatively high joint efficiency.
文摘The temperature field and thermal cycling curve in the heat-affected zone during welding 400 MPa ultra fine grained steel by plasma arc were simulated using finite element method. The principle of grain growth kinetics was used to predict the grain size in the heat-affected zone under different welding parameters. The simulation results show that the growing tendency of HAZ grain could be controlled by adjusting the welding parameters, but the growth of HAZ grain could not be eliminated at all. The HAZ grain size became small with increasing of the cooling rate and added with increasing of welding current, arc voltage and welding speed.
