Numerical simulations are performed to examine the packing behavior of human red blood cells(RBCs). A combined ?nite-discrete element method(FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhes...Numerical simulations are performed to examine the packing behavior of human red blood cells(RBCs). A combined ?nite-discrete element method(FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhesion solid bodies. The packed volume and the void ratio of a large number of randomly packed RBCs are clari?ed,and the effects of the RBC shape, the mesh size, the cell number, and the container size are investigated. The results show that the packed human RBCs with normal shape have a void ratio of 28.45%, which is slightly higher than that of the ?at or thick cells used in this study. Such information is bene?cial to the further understanding on the geometric features of human RBCs and the research on RBC simulations.展开更多
The aim of this study is to investigate the asphalt mixture anisotropy of both the modulus and Poisson＇s ratio due to air voids using a discrete element modeling simulation method. Three three-dimensional cubic digit...The aim of this study is to investigate the asphalt mixture anisotropy of both the modulus and Poisson＇s ratio due to air voids using a discrete element modeling simulation method. Three three-dimensional cubic digital samples of asphalt mixture with different shapes of single air void were built using discrete element software PFC^（3D）. The aggregate gradation, air voids and mastic included in the digital samples were modeled using different contact models, with due consideration of the volumetric fractions of the different phases. Laboratory uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. Simulation of the uniaxial cyclic compressive tests was performed on the three cubic samples loaded in three different directions. Dynamic modulus in three directions and Poisson＇s ratio in six directions were calculated from the compression stress-strain responses. Results show that both the modulus and Poisson＇s ratio are dependent on the preferential orientation of air voids. The anisotropy of the modulus and Poisson＇s ratio increases as the pressure loading on the asphalt mixture increases. Compared to the modulus, Poisson＇s ratio due to air voids has been shown to be more anisotropic. The maximum of Poisson＇s ratio and modulus is shown to be up to 80% and 11% higher than the minimum, respectively.展开更多
The influence of crystallographic orientation on the void growth in FCC crystals was numerically simulated with 3D crystal plasticity finite element by using a 3D unit cell including a spherical void,and the rate-depe...The influence of crystallographic orientation on the void growth in FCC crystals was numerically simulated with 3D crystal plasticity finite element by using a 3D unit cell including a spherical void,and the rate-dependent crystal plasticity theory was implemented as a user material subroutine.The results of the simulations show that crystallographic orientation has significant influence on the growth behavior of the void.Different active slip systems of the regions around the void cause the discontinuity in lattice rotation around the void,and the corner-like region is formed.In the case of the void located at grain boundary,large heterogeneous deformation occurs between the two grains,and the equivalent plastic deformation along grain boundary near the void in the case of θ=45°(θ is the angle between grain boundary direction and X-axis) is larger than the others.Large difference of orientation factor of the two grains leads to large equivalent plastic deformation along grain boundary,and the unit cell is more likely to fail by intergranular fracture.展开更多
空腔嵌入绝缘体上硅(void embedded silicon on insulator,VESOI)衬底是一种面向新型互补金属氧化物半导体(complementary metal oxide semiconductor,CMOS)器件及集成技术的新型SOI衬底材料.当采用离子剥离技术制备该衬底时,由氢气形...空腔嵌入绝缘体上硅(void embedded silicon on insulator,VESOI)衬底是一种面向新型互补金属氧化物半导体(complementary metal oxide semiconductor,CMOS)器件及集成技术的新型SOI衬底材料.当采用离子剥离技术制备该衬底时,由氢气形成的板状气泡会聚集在衬底剥离界面,对空腔结构产生挤压作用,并有可能造成空腔结构的破损,因而有必要对VESOI衬底制备过程中的应力机制和工艺稳定性进行深入研究.本文以单个矩形空腔结构为研究对象,借助固支梁理论分析了其在工艺制备过程中的力学状态,并利用有限元工具构建了其三维几何模型.通过应力仿真,找到了该空腔结构的破裂失效原因,并确认了其脆弱位点.结果表明,矩形空腔结构短边长度w、顶硅薄膜厚度t以及氢气泡压力是影响顶硅薄膜应力状态的主要因素.当w/t值超过4—5时,硅薄膜将因应力过大而破裂,破裂位点分布于空腔结构长边方向.通过优化顶层硅厚度t,以及内嵌空腔结构、尺寸,本工作成功制备了符合CMOS产线要求的高质量8 in(1 in=2.54 cm)VESOI衬底.该工作对基于VESOI衬底的集成技术具有较好参考价值.展开更多
基金Project supported by the Engineering and Physical Sciences Research Council(EPSRC)Turbulence Consortium Grant(No.EP/G069581/1)the Marie Curie International Incoming Fellowship(No.PIIF-GA-253453)
文摘Numerical simulations are performed to examine the packing behavior of human red blood cells(RBCs). A combined ?nite-discrete element method(FDEM) is utilized, in which the RBCs are modeled as no-friction and no-adhesion solid bodies. The packed volume and the void ratio of a large number of randomly packed RBCs are clari?ed,and the effects of the RBC shape, the mesh size, the cell number, and the container size are investigated. The results show that the packed human RBCs with normal shape have a void ratio of 28.45%, which is slightly higher than that of the ?at or thick cells used in this study. Such information is bene?cial to the further understanding on the geometric features of human RBCs and the research on RBC simulations.
基金Funded by the National Natural Science Foundation of China(No.51208178)the Fundamental Research Funds for the Central Universities(No.2015B17014)
文摘The aim of this study is to investigate the asphalt mixture anisotropy of both the modulus and Poisson＇s ratio due to air voids using a discrete element modeling simulation method. Three three-dimensional cubic digital samples of asphalt mixture with different shapes of single air void were built using discrete element software PFC^（3D）. The aggregate gradation, air voids and mastic included in the digital samples were modeled using different contact models, with due consideration of the volumetric fractions of the different phases. Laboratory uniaxial complex modulus test and indirect tensile strength test were conducted to obtain material input parameters for numerical modeling. Simulation of the uniaxial cyclic compressive tests was performed on the three cubic samples loaded in three different directions. Dynamic modulus in three directions and Poisson＇s ratio in six directions were calculated from the compression stress-strain responses. Results show that both the modulus and Poisson＇s ratio are dependent on the preferential orientation of air voids. The anisotropy of the modulus and Poisson＇s ratio increases as the pressure loading on the asphalt mixture increases. Compared to the modulus, Poisson＇s ratio due to air voids has been shown to be more anisotropic. The maximum of Poisson＇s ratio and modulus is shown to be up to 80% and 11% higher than the minimum, respectively.
基金Project(2005CB623706) supported by the Major State Basic Research Development Program of China
文摘The influence of crystallographic orientation on the void growth in FCC crystals was numerically simulated with 3D crystal plasticity finite element by using a 3D unit cell including a spherical void,and the rate-dependent crystal plasticity theory was implemented as a user material subroutine.The results of the simulations show that crystallographic orientation has significant influence on the growth behavior of the void.Different active slip systems of the regions around the void cause the discontinuity in lattice rotation around the void,and the corner-like region is formed.In the case of the void located at grain boundary,large heterogeneous deformation occurs between the two grains,and the equivalent plastic deformation along grain boundary near the void in the case of θ=45°(θ is the angle between grain boundary direction and X-axis) is larger than the others.Large difference of orientation factor of the two grains leads to large equivalent plastic deformation along grain boundary,and the unit cell is more likely to fail by intergranular fracture.
