Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "c...Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "cloud-like" configuration, which brings difficulties in quantifying the effective performance of defected casting. In this paper, the influences of random shrinkage porosity on the equivalent elastic modulus of QT400-18 casting were studied by a numerical statistics approach. An improved random algorithm was applied into the lattice model to simulate the "cloud-like" morphology of shrinkage porosity. Then, a large number of numerical samples containing random levels of shrinkage were generated by the proposed algorithm. The stress concentration factor and equivalent elastic modulus of these numerical samples were calculated. Based on a statistical approach, the effects of shrinkage porosity's distribution characteristics, such as area fraction, shape, and relative location on the casting's equivalent mechanical properties were discussed respectively. It is shown that the approach with randomly distributed defects has better predictive capabilities than traditional methods. The following conclusions can be drawn from the statistical simulations:(1) the effective modulus decreases remarkably if the shrinkage porosity percent is greater than 1.5%;(2) the average Stress Concentration Factor(SCF) produced by shrinkage porosity is about 2.0;(3) the defect's length across the loading direction plays a more important role in the effective modulus than the length along the loading direction;(4) the surface defect perpendicular to loading direction reduces the mean modulus about 1.5% more than a defect of other position.展开更多
In order to eliminate displacement and elastic deformation between images of adjacent frames in course of 3D ultrasonic image reconstruction, elastic registration based on skeleton feature was adopt in this paper. A n...In order to eliminate displacement and elastic deformation between images of adjacent frames in course of 3D ultrasonic image reconstruction, elastic registration based on skeleton feature was adopt in this paper. A new automatically skeleton tracking extract algorithm is presented, which can extract connected skeleton to express figure feature. Feature points of connected skeleton are extracted automatically by accounting topical curvature extreme points several times. Initial registration is processed according to barycenter of skeleton. Whereafter, elastic registration based on radial basis function are processed according to feature points of skeleton. Result of example demonstrate that according to traditional rigid registration, elastic registration based on skeleton feature retain natural difference in shape for organ’s different part, and eliminate slight elastic deformation between frames caused by image obtained process simultaneously. This algorithm has a high practical value for image registration in course of 3D ultrasound image reconstruction.展开更多
Ultrasonic wave testing was applied to investigate the quality and weathering status of rock specimens obtained in two borings situated in the Xishan Buddha rock slope in Taiyuan, China. This paper pays special attent...Ultrasonic wave testing was applied to investigate the quality and weathering status of rock specimens obtained in two borings situated in the Xishan Buddha rock slope in Taiyuan, China. This paper pays special attention to the distribution of bulk density, dynamic parameters and static parameters of rock specimens as well as the relationship between static and dynamic parameters. The results illustrate that the distribution of both parameters is identical along the depth of two drilled holes in the rock slope. When the hole depth increases, the density of rock mass, saturated compression strength and static elastic modulus, dynamic elastic modulus and wave velocity also show increase tendency. The weathering degree in the rock mass ranging from the surface of cliff to the depth of 2.5 m is the highest while the rock mass is unsalted and more rigid when the depth is larger than 3.0 m. The relationship between dynamic elastic modulus, sonic wave velocity and horizontal depth indicates that dynamic elastic modulus is more sensitive than sonic wave velocity. Conversely, by comparing quantity relationship between static elastic modulus and sonic wave velocity, it is found that the composition of rock has a great influence on the relationship between static and dynamic parameters, that is, inequality of rock composition will lead to dispersion and abnormality of the distribution of static and dynamic parameters.展开更多
This paper presents an analytical layer-element method used to analyze the displacement of a multi-layered transversely isotropic elastic medium of arbitrary depth subjected to axisymmetric loading.Based on the basic ...This paper presents an analytical layer-element method used to analyze the displacement of a multi-layered transversely isotropic elastic medium of arbitrary depth subjected to axisymmetric loading.Based on the basic constitutive equations and the HU Hai-chang's solutions for transversely isotropic elastic media,the state vectors of a multi-layered transversely isotropic medium were deduced.From the state vectors,an analytical layer element for a single layer(i.e.,a symmetric and exact stiffness matrix) was acquired in the Hankel transformed domain,which not only simplified the calculation but also improved the numerical efficiency and stability due to the absence of positive exponential functions.The global stiffness matrix was obtained by assembling the interrelated layer elements based on the principle of the finite layer method.By solving the algebraic equations of the global stiffness matrix which satisfy the boundary conditions,the solutions for multi-layered transversely isotropic media in the Hankel transformed domain were obtained.The actual solutions of this problem in the physical domain were acquired by inverting the Hankel transform.This paper presents numerical examples to verify the proposed solutions and investigate the influence of the properties of the multi-layered medium on the load-displacement response.展开更多
In this paper,an automatic unstructured focused ion beam(FIB) and scanning electron microscopy(SEM) images induced representative volume element(RVE) finite element(FE) method is developed to predict submicron scale c...In this paper,an automatic unstructured focused ion beam(FIB) and scanning electron microscopy(SEM) images induced representative volume element(RVE) finite element(FE) method is developed to predict submicron scale carbonate rock effective Young's and bulk moduli and Poisson's ratio on parallel CPU-GPU platform.Based on high resolution-contrast surface morphology and internal fabnc-texture structure images from carbonate rock specimen(covered 0.12-64 μm^2 area and8000 μm^3 domain),the cubic RVE FE models are constructed from different sites through Avizo with user-defined parameters Matlab coding.The effective Young's and bulk moduli and Poisson's ratio of the different RVEs and porosity and pore size are computed by using periodic boundary condition in the well-known FE software Abaqus.FE mesh sensitivity analysis has been conducted where all moduli converge to a certain constant value at larger FE mesh density.The effect of fabric-texture(pore size,shape,and distribution) on the elastic properties is discussed.The correlations between the computed effective elastic properties and pore size,porosity,RVE size have been established.The simulation results show that the effective Young's and bulk moduli and Poisson's ratio have strong anisotropic behavior and depend on RVE size,porosity and pore size.The RVE size,porosity and pore size are three independent factors in affecting of the effective elastic moduli,the effect mechanism of porosity and pore size is same while the effect mechanism of RVE size is difference.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51305350)the Basic Research Foundation of NWPU(No.3102014JCQ01045)
文摘Shrinkage porosity is a type of random distribution defects and exists in most large castings. Different from the periodic symmetry defects or certain distribution defects, shrinkage porosity presents a random "cloud-like" configuration, which brings difficulties in quantifying the effective performance of defected casting. In this paper, the influences of random shrinkage porosity on the equivalent elastic modulus of QT400-18 casting were studied by a numerical statistics approach. An improved random algorithm was applied into the lattice model to simulate the "cloud-like" morphology of shrinkage porosity. Then, a large number of numerical samples containing random levels of shrinkage were generated by the proposed algorithm. The stress concentration factor and equivalent elastic modulus of these numerical samples were calculated. Based on a statistical approach, the effects of shrinkage porosity's distribution characteristics, such as area fraction, shape, and relative location on the casting's equivalent mechanical properties were discussed respectively. It is shown that the approach with randomly distributed defects has better predictive capabilities than traditional methods. The following conclusions can be drawn from the statistical simulations:(1) the effective modulus decreases remarkably if the shrinkage porosity percent is greater than 1.5%;(2) the average Stress Concentration Factor(SCF) produced by shrinkage porosity is about 2.0;(3) the defect's length across the loading direction plays a more important role in the effective modulus than the length along the loading direction;(4) the surface defect perpendicular to loading direction reduces the mean modulus about 1.5% more than a defect of other position.
文摘In order to eliminate displacement and elastic deformation between images of adjacent frames in course of 3D ultrasonic image reconstruction, elastic registration based on skeleton feature was adopt in this paper. A new automatically skeleton tracking extract algorithm is presented, which can extract connected skeleton to express figure feature. Feature points of connected skeleton are extracted automatically by accounting topical curvature extreme points several times. Initial registration is processed according to barycenter of skeleton. Whereafter, elastic registration based on radial basis function are processed according to feature points of skeleton. Result of example demonstrate that according to traditional rigid registration, elastic registration based on skeleton feature retain natural difference in shape for organ’s different part, and eliminate slight elastic deformation between frames caused by image obtained process simultaneously. This algorithm has a high practical value for image registration in course of 3D ultrasound image reconstruction.
文摘Ultrasonic wave testing was applied to investigate the quality and weathering status of rock specimens obtained in two borings situated in the Xishan Buddha rock slope in Taiyuan, China. This paper pays special attention to the distribution of bulk density, dynamic parameters and static parameters of rock specimens as well as the relationship between static and dynamic parameters. The results illustrate that the distribution of both parameters is identical along the depth of two drilled holes in the rock slope. When the hole depth increases, the density of rock mass, saturated compression strength and static elastic modulus, dynamic elastic modulus and wave velocity also show increase tendency. The weathering degree in the rock mass ranging from the surface of cliff to the depth of 2.5 m is the highest while the rock mass is unsalted and more rigid when the depth is larger than 3.0 m. The relationship between dynamic elastic modulus, sonic wave velocity and horizontal depth indicates that dynamic elastic modulus is more sensitive than sonic wave velocity. Conversely, by comparing quantity relationship between static elastic modulus and sonic wave velocity, it is found that the composition of rock has a great influence on the relationship between static and dynamic parameters, that is, inequality of rock composition will lead to dispersion and abnormality of the distribution of static and dynamic parameters.
基金Project (No.50578121) supported by the National Natural Science Foundation of China
文摘This paper presents an analytical layer-element method used to analyze the displacement of a multi-layered transversely isotropic elastic medium of arbitrary depth subjected to axisymmetric loading.Based on the basic constitutive equations and the HU Hai-chang's solutions for transversely isotropic elastic media,the state vectors of a multi-layered transversely isotropic medium were deduced.From the state vectors,an analytical layer element for a single layer(i.e.,a symmetric and exact stiffness matrix) was acquired in the Hankel transformed domain,which not only simplified the calculation but also improved the numerical efficiency and stability due to the absence of positive exponential functions.The global stiffness matrix was obtained by assembling the interrelated layer elements based on the principle of the finite layer method.By solving the algebraic equations of the global stiffness matrix which satisfy the boundary conditions,the solutions for multi-layered transversely isotropic media in the Hankel transformed domain were obtained.The actual solutions of this problem in the physical domain were acquired by inverting the Hankel transform.This paper presents numerical examples to verify the proposed solutions and investigate the influence of the properties of the multi-layered medium on the load-displacement response.
基金supported by the National Natural Science Foundation of China(Grant No.41404078)
文摘In this paper,an automatic unstructured focused ion beam(FIB) and scanning electron microscopy(SEM) images induced representative volume element(RVE) finite element(FE) method is developed to predict submicron scale carbonate rock effective Young's and bulk moduli and Poisson's ratio on parallel CPU-GPU platform.Based on high resolution-contrast surface morphology and internal fabnc-texture structure images from carbonate rock specimen(covered 0.12-64 μm^2 area and8000 μm^3 domain),the cubic RVE FE models are constructed from different sites through Avizo with user-defined parameters Matlab coding.The effective Young's and bulk moduli and Poisson's ratio of the different RVEs and porosity and pore size are computed by using periodic boundary condition in the well-known FE software Abaqus.FE mesh sensitivity analysis has been conducted where all moduli converge to a certain constant value at larger FE mesh density.The effect of fabric-texture(pore size,shape,and distribution) on the elastic properties is discussed.The correlations between the computed effective elastic properties and pore size,porosity,RVE size have been established.The simulation results show that the effective Young's and bulk moduli and Poisson's ratio have strong anisotropic behavior and depend on RVE size,porosity and pore size.The RVE size,porosity and pore size are three independent factors in affecting of the effective elastic moduli,the effect mechanism of porosity and pore size is same while the effect mechanism of RVE size is difference.
