Separated specimens of Ti-6Al-4V alloy were dynamically loaded at a strain rate of 3 900 s-1 using a split Hopkinson pressure bar（SHPB） apparatus.The fracture features of the separated specimens were investigated by...Separated specimens of Ti-6Al-4V alloy were dynamically loaded at a strain rate of 3 900 s-1 using a split Hopkinson pressure bar（SHPB） apparatus.The fracture features of the separated specimens were investigated by a scanning electron microscope.The results show that adiabatic shear failure occurs in the tested specimens,and two typical areas（dimple and smooth areas） with different features are alternatively distributed on the whole fracture surface.The dimple areas originate from voids generation and coalescence,exhibiting ductile fracture characteristics.Simultaneously,ultrafine grains（UFGs） and microcracks among grains are observed on the smooth areas,indicating that the emergence of UFG areas is caused by the propagation of microcracks along grain boundaries and exhibits brittle fracture characteristics.Fracture occurring in adiabatic shear bands is not uniform and ultimate rupture is resulted from ductile and brittle fracture modes.展开更多
According to the coal or rock cutting theory, a mechanical model and computing formula for a pick and the drum load fluctuation model were established in order to obtain relationships between pick arrangements and dru...According to the coal or rock cutting theory, a mechanical model and computing formula for a pick and the drum load fluctuation model were established in order to obtain relationships between pick arrangements and drum fluctuation loads, drum rotary speeds and haulage speeds. Based on a minimum load fluctuation, an optimal mathematical model was established for drum pick arrangements. The effects of pick arrangements （including punnett square, sequence, aberrance Ⅰ and Ⅱ） on the drum load fluctuation coefficient are discussed. The relationships between the pick arrangements of the drum with different start vanes and the cutting load fluctuation coefficient, the drum rotary speed and haulage speed were also studied. The results indicate that the punnett square arrangement has a smaller cutting load fluctuation coefficient than other forms of arrangement and the drum with the 4-start vanes has the smallest coefficient. The drum rotary speed and haulage speed are affected not only by pick arrangements, but also by the number of vanes.展开更多
A coaxial mixer meeting the actual demand of a system with high and variable viscosity is investigated. It has an outer wall-scraping frame and a double inner impeller consisting of a four-pitched-blade turbine and Ru...A coaxial mixer meeting the actual demand of a system with high and variable viscosity is investigated. It has an outer wall-scraping frame and a double inner impeller consisting of a four-pitched-blade turbine and Rushton turbine. The power consumption and flow field characteristics of the coaxial mixer in laminar and transitional flow are simulated numerically, and then the distribution of velocity field, shear rate and mass flow rate are analyzed. The simulation results indicate that the outer frame has little effect on the power consumption of the double inner impeller whether in laminar or transitional flow, whereas the inner combined impeller has a great effect on the power consumption of the outer frame. Compared with the single rotation mode, the power consumption of the outer frame will decrease in co-rotation mode and increase in counter-rotation mode. The velocity, shear rate and mass flow rate are relatively high near the inner impeller in all operating modes, and only under double-shaft agitation will the mixing performance near the free surface be improved.In addition, these distributions in the co-rotation and counter-rotation modes show little difference, but the co-rotation mode is recommended for the advantage of low power consumption.展开更多
The pressure signal in the lifting cylinder of the shearer is selected as feature signal, its mean-square deviation is extracted as the feature variable in this paper. The authors put forward a new method of recognizi...The pressure signal in the lifting cylinder of the shearer is selected as feature signal, its mean-square deviation is extracted as the feature variable in this paper. The authors put forward a new method of recognizing the shearer’s cutting state based on pattern recognition. According to this, the completed controI software produced a satisfactory experiment result on the artificial longwall face in the laboratory, Finally the authors look forward to the prospect of the introduction of the artificial neural network theory into this field.展开更多
Metamorphic core complex(MCC) is characterized by the exhumation of lower crust over a large-scale detachment fault, providing natural records for tectonic extension. MCCs are widely identified in the North China Crat...Metamorphic core complex(MCC) is characterized by the exhumation of lower crust over a large-scale detachment fault, providing natural records for tectonic extension. MCCs are widely identified in the North China Craton(NCC), which have been intensively studied on their structural and geological characteristics. Yet, the condition for the formation of MCCs and their link with NCC destruction are still in debate. In this study, we perform numerical simulations to investigate MCC formation under extension, with a focus on the effect of crustal rheologies. Results indicate that three end-member modes of deformation may occur: the metamorphic core complex mode, the detachment fault-uplifting mode and the pure shear mode. Weaker lower crust and stronger upper crust may promote the formation of MCC. In contrast, stronger lower crust(>1.3×1021 Pa s) may prohibit the exhumation of lower crust(detachment fault-uplifting mode), while weaker upper crust(<7.8×1021 Pa s) may fail to develop detachment faults(pure shear mode). Given that cratons typically have a strong crust, we suggest that the lower crust of NCC was weakened prior to extension, which promoted the formation of MCC in a later stage under the back-arc extension.展开更多
文摘Separated specimens of Ti-6Al-4V alloy were dynamically loaded at a strain rate of 3 900 s-1 using a split Hopkinson pressure bar（SHPB） apparatus.The fracture features of the separated specimens were investigated by a scanning electron microscope.The results show that adiabatic shear failure occurs in the tested specimens,and two typical areas（dimple and smooth areas） with different features are alternatively distributed on the whole fracture surface.The dimple areas originate from voids generation and coalescence,exhibiting ductile fracture characteristics.Simultaneously,ultrafine grains（UFGs） and microcracks among grains are observed on the smooth areas,indicating that the emergence of UFG areas is caused by the propagation of microcracks along grain boundaries and exhibits brittle fracture characteristics.Fracture occurring in adiabatic shear bands is not uniform and ultimate rupture is resulted from ductile and brittle fracture modes.
文摘According to the coal or rock cutting theory, a mechanical model and computing formula for a pick and the drum load fluctuation model were established in order to obtain relationships between pick arrangements and drum fluctuation loads, drum rotary speeds and haulage speeds. Based on a minimum load fluctuation, an optimal mathematical model was established for drum pick arrangements. The effects of pick arrangements （including punnett square, sequence, aberrance Ⅰ and Ⅱ） on the drum load fluctuation coefficient are discussed. The relationships between the pick arrangements of the drum with different start vanes and the cutting load fluctuation coefficient, the drum rotary speed and haulage speed were also studied. The results indicate that the punnett square arrangement has a smaller cutting load fluctuation coefficient than other forms of arrangement and the drum with the 4-start vanes has the smallest coefficient. The drum rotary speed and haulage speed are affected not only by pick arrangements, but also by the number of vanes.
基金Supported by the Fundamental Research Funds for the Central Universities(2012QNA4018)the National Natural Science foundation of China(21206144)the Program for Zhejiang Leading Team of S&T Innovation(2011R50005)
文摘A coaxial mixer meeting the actual demand of a system with high and variable viscosity is investigated. It has an outer wall-scraping frame and a double inner impeller consisting of a four-pitched-blade turbine and Rushton turbine. The power consumption and flow field characteristics of the coaxial mixer in laminar and transitional flow are simulated numerically, and then the distribution of velocity field, shear rate and mass flow rate are analyzed. The simulation results indicate that the outer frame has little effect on the power consumption of the double inner impeller whether in laminar or transitional flow, whereas the inner combined impeller has a great effect on the power consumption of the outer frame. Compared with the single rotation mode, the power consumption of the outer frame will decrease in co-rotation mode and increase in counter-rotation mode. The velocity, shear rate and mass flow rate are relatively high near the inner impeller in all operating modes, and only under double-shaft agitation will the mixing performance near the free surface be improved.In addition, these distributions in the co-rotation and counter-rotation modes show little difference, but the co-rotation mode is recommended for the advantage of low power consumption.
文摘The pressure signal in the lifting cylinder of the shearer is selected as feature signal, its mean-square deviation is extracted as the feature variable in this paper. The authors put forward a new method of recognizing the shearer’s cutting state based on pattern recognition. According to this, the completed controI software produced a satisfactory experiment result on the artificial longwall face in the laboratory, Finally the authors look forward to the prospect of the introduction of the artificial neural network theory into this field.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 41304074, 91014006 & 91414301)
文摘Metamorphic core complex(MCC) is characterized by the exhumation of lower crust over a large-scale detachment fault, providing natural records for tectonic extension. MCCs are widely identified in the North China Craton(NCC), which have been intensively studied on their structural and geological characteristics. Yet, the condition for the formation of MCCs and their link with NCC destruction are still in debate. In this study, we perform numerical simulations to investigate MCC formation under extension, with a focus on the effect of crustal rheologies. Results indicate that three end-member modes of deformation may occur: the metamorphic core complex mode, the detachment fault-uplifting mode and the pure shear mode. Weaker lower crust and stronger upper crust may promote the formation of MCC. In contrast, stronger lower crust(>1.3×1021 Pa s) may prohibit the exhumation of lower crust(detachment fault-uplifting mode), while weaker upper crust(<7.8×1021 Pa s) may fail to develop detachment faults(pure shear mode). Given that cratons typically have a strong crust, we suggest that the lower crust of NCC was weakened prior to extension, which promoted the formation of MCC in a later stage under the back-arc extension.
