A user-defined micromechanical model was developed to investigate the fracture mechanism of asphalt concrete （AC） using the discrete element method （DEM）. A three-dimensional （3D） AC beam was built using the ＂F...A user-defined micromechanical model was developed to investigate the fracture mechanism of asphalt concrete （AC） using the discrete element method （DEM）. A three-dimensional （3D） AC beam was built using the ＂Fish＂ language provided by PFC3D and was employed to simulate the three-point bending beam test at two temperature levels： -10 ℃ and 15℃. The AC beam was modeled with the consideration of the microstructural features of asphalt mixtures. Uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. The 3D predictions were validated using laboratory experimental measurements of AC beams prepared by the same mixture design. Effects of mastic stiffness, cohesive and adhesive strength on AC fracture behavior were investigated using the DEM model. The results show that the 3D DEM fracture model can accurately predict the fracture patterns of asphalt concrete. The ratio of stress at interfaces to the stress in mastics increases as the mastic stiffness decreases; however, the increase in the cohesive strength or adhesive strength shows no significant influence on the tensile strength.展开更多
A precise friction model is essential for the prediction of tyre wet grip performance and optimization of pavement surface texture design.A mechanical system for predicting the wet grip potential of asphalt pavement w...A precise friction model is essential for the prediction of tyre wet grip performance and optimization of pavement surface texture design.A mechanical system for predicting the wet grip potential of asphalt pavement was systematically presented using an extended rubber material model by a time step integration scheme.This analytical approach was transferred to a 2D numerical multi-body system consisting of interconnected masses,coupling spring and elementary rubber element of a generalized Maxwell model of rubber tyre tread.The system consists of two basic modules with the same program structure and algorithm,considering the frequency-,temperature-,and strain-dependency behaviors of the complex dynamic modulus of rubber element.The dependence of penetration depth and friction coefficient on the velocity was simulated and validated.It can be concluded that this system can be used for predicting the wet grip potential of asphalt pavements.展开更多
By using petrological,isotope chronological,and geochemical methods,the authors studied the volcanic rocks in the studied area,mainly including dacites and trachytes. The results show that they formed during the late ...By using petrological,isotope chronological,and geochemical methods,the authors studied the volcanic rocks in the studied area,mainly including dacites and trachytes. The results show that they formed during the late Early Cretaceous. Geochemically,the volcanic rocks are relatively enriched in large-ion lithophile elements( Rb,K,and Th) and depleted in high field strength elements( Nb,Ta,and Ti),and rich in light rare earth elements,and depleted in heavy rare earth elements. The fact indicates that the main body of the volcanic rocks in the Qushenla Formation was derived from the partial melting of lower crust. The lithological assemblages are characterized by continental high-K calc-alkaline and shoshonitic series,suggesting that the southward-subducting oceanic slab in southern Bangong Lake had break off and that the Bangong Lake-Nujiang Ocean had closed before 107 Ma. The main dynamic mechanisms for the genesis of this set of intermediate-acidic volcanic rocks were upwelling of the asthenosphere and partial melting of the lower crust caused by slab break-off.展开更多
The varicoloured Fenghuoshan Group occurs widely in the Qiangtang-Hoh Xil region of the northern Qinghai-Xizang Plateau. Few fossils have been found to date in this sedimentary succession because lithological conditio...The varicoloured Fenghuoshan Group occurs widely in the Qiangtang-Hoh Xil region of the northern Qinghai-Xizang Plateau. Few fossils have been found to date in this sedimentary succession because lithological conditions are not conducive to their preservation. As a result, there has been a long-term disagreement among geologists about its age. Despite a few lists of fossil names in individual publi- cations, no detailed research on the palaeontology, including palynology, has been reported previously. In this study, we recovered many pollen grains and spores from two samples that were collected on the northern slope of Fenghuo Moun- tain. They indicate an age no younger than Maastrichtian for the upper part of the Fenghuoshan Group. It is considered likely that the entire Fenghuoshan Group represents deposi- tion between the late Early Cretaceous （possibly Albian） and the Maastrichtian. The palynoflora consists mainly of angio- sperm pollen, gymnosperm pollen and fern and bryophyte spores being subordinate. Pollen grains referable to the Ephedrales and the Taxaceae-Cupressaceae groups dominate the assemblage, implying a warm, arid climate and subtropical forest-shrub vegetation at the time of deposition.展开更多
基金Project(51208178)supported by the National Natural Science Foundation of ChinaProject(2012M520991)supported by China Postdoctoral Science Foundation
文摘A user-defined micromechanical model was developed to investigate the fracture mechanism of asphalt concrete （AC） using the discrete element method （DEM）. A three-dimensional （3D） AC beam was built using the ＂Fish＂ language provided by PFC3D and was employed to simulate the three-point bending beam test at two temperature levels： -10 ℃ and 15℃. The AC beam was modeled with the consideration of the microstructural features of asphalt mixtures. Uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. The 3D predictions were validated using laboratory experimental measurements of AC beams prepared by the same mixture design. Effects of mastic stiffness, cohesive and adhesive strength on AC fracture behavior were investigated using the DEM model. The results show that the 3D DEM fracture model can accurately predict the fracture patterns of asphalt concrete. The ratio of stress at interfaces to the stress in mastics increases as the mastic stiffness decreases; however, the increase in the cohesive strength or adhesive strength shows no significant influence on the tensile strength.
基金Project(FP6-PL-0506437) supported by European CommissionProject(50908053) supported by the National Natural Science Foundation of China
文摘A precise friction model is essential for the prediction of tyre wet grip performance and optimization of pavement surface texture design.A mechanical system for predicting the wet grip potential of asphalt pavement was systematically presented using an extended rubber material model by a time step integration scheme.This analytical approach was transferred to a 2D numerical multi-body system consisting of interconnected masses,coupling spring and elementary rubber element of a generalized Maxwell model of rubber tyre tread.The system consists of two basic modules with the same program structure and algorithm,considering the frequency-,temperature-,and strain-dependency behaviors of the complex dynamic modulus of rubber element.The dependence of penetration depth and friction coefficient on the velocity was simulated and validated.It can be concluded that this system can be used for predicting the wet grip potential of asphalt pavements.
基金Supported by project of National Natural Science Foundation of China(No.41172056)
文摘By using petrological,isotope chronological,and geochemical methods,the authors studied the volcanic rocks in the studied area,mainly including dacites and trachytes. The results show that they formed during the late Early Cretaceous. Geochemically,the volcanic rocks are relatively enriched in large-ion lithophile elements( Rb,K,and Th) and depleted in high field strength elements( Nb,Ta,and Ti),and rich in light rare earth elements,and depleted in heavy rare earth elements. The fact indicates that the main body of the volcanic rocks in the Qushenla Formation was derived from the partial melting of lower crust. The lithological assemblages are characterized by continental high-K calc-alkaline and shoshonitic series,suggesting that the southward-subducting oceanic slab in southern Bangong Lake had break off and that the Bangong Lake-Nujiang Ocean had closed before 107 Ma. The main dynamic mechanisms for the genesis of this set of intermediate-acidic volcanic rocks were upwelling of the asthenosphere and partial melting of the lower crust caused by slab break-off.
基金supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences(XDB03010103)the National Basic Research Program of China(2012CB822004)the National Natural Science Foundation of China(41172011)
文摘The varicoloured Fenghuoshan Group occurs widely in the Qiangtang-Hoh Xil region of the northern Qinghai-Xizang Plateau. Few fossils have been found to date in this sedimentary succession because lithological conditions are not conducive to their preservation. As a result, there has been a long-term disagreement among geologists about its age. Despite a few lists of fossil names in individual publi- cations, no detailed research on the palaeontology, including palynology, has been reported previously. In this study, we recovered many pollen grains and spores from two samples that were collected on the northern slope of Fenghuo Moun- tain. They indicate an age no younger than Maastrichtian for the upper part of the Fenghuoshan Group. It is considered likely that the entire Fenghuoshan Group represents deposi- tion between the late Early Cretaceous （possibly Albian） and the Maastrichtian. The palynoflora consists mainly of angio- sperm pollen, gymnosperm pollen and fern and bryophyte spores being subordinate. Pollen grains referable to the Ephedrales and the Taxaceae-Cupressaceae groups dominate the assemblage, implying a warm, arid climate and subtropical forest-shrub vegetation at the time of deposition.
