The propagation mechanism of microcracks in nanocrystalline single crystal systems under uniaxial dynamic and static tension is investigated using the phase-field-crystal method.Both dynamic and static stretching resu...The propagation mechanism of microcracks in nanocrystalline single crystal systems under uniaxial dynamic and static tension is investigated using the phase-field-crystal method.Both dynamic and static stretching results show that different orientation angles can induce the crack propagation mode,microscopic morphology,the free energy,crack area change,and causing fracture failure.Crack propagation mode depends on the dislocation activity near the crack tip.Brittle propagation of the crack occurs due to dislocation always at crack tip.Dislocation is emitted at the front end of the crack tip and plastic deformation occurs,which belongs to ductile propagation.The orientation angles of 9°and 14°are brittleductile mixed propagation,while the orientation angles of 19°and 30°are brittle propagation and no dislocation is formed under dynamic tension.The vacancy and vacancy connectivity phenomenon would appear when the orientation angle is14°under static tension,and the crack would be ductile propagation.While the orientation angle is 19°and 30°,the crack propagates in a certain direction,which is a kind of brittle propagation.This work has some practical significance in preventing material fracture failure and improving material performance.展开更多
Orientation optimization plays an important role in the lay-up design of composite structures.Earlier orientation optimization methods face the main problem of huge number of design variables.Recently,a patch concept ...Orientation optimization plays an important role in the lay-up design of composite structures.Earlier orientation optimization methods face the main problem of huge number of design variables.Recently,a patch concept is proposed to reduce the number of design variables.However,the traditional stress-based method can not deal with patch orientation optimization of composite structures.In this paper,we propose an extended stress-based method to deal with such problems.The considered problems are to minimize the mean compliance under multiple load cases or to maximize the eigenvalues of a composite structure.Four numerical examples are solved to demonstrate the efficiency of the new method.It is shown that the new method has the ability to deal with constraints on orientation angle,such as symmetric,antisymmetric and discrete orientation angle constraints.The iteration is less time-consuming because no sensitivity analysis is needed and a quick convergence rate can be achieved.展开更多
The scattering-model-based(SMB)speckle filtering for polarimetric SAR(Pol SAR)data is reasonably effective in preserving dominant scattering mechanisms.However,the efficiency strongly depends on the accuracies of both...The scattering-model-based(SMB)speckle filtering for polarimetric SAR(Pol SAR)data is reasonably effective in preserving dominant scattering mechanisms.However,the efficiency strongly depends on the accuracies of both the decomposition and classification of the scattering properties.In addition,a relatively weak speckle reduction particularly in distributed media was reported in the related literatures.In this work,an improved SMB filtering strategy is proposed considering the aforementioned deficiencies.First,the orientation angle compensation is incorporated into the SMB filtering process to remedy the overestimation of the volume scattering contribution in the Freeman-Durden decomposition.In addition,an algorithm to select the homogenous pixels is developed based on the spatial majority rule for adaptive speckle reduction.We demonstrate the superiority of the proposed methods in terms of scattering property preservation and speckle noise reduction using L-band Pol SAR data sets of San Francisco that were acquired by the NASA/JPL airborne SAR(AIRSAR)system.展开更多
The orientation angle is an important parameter that reflects the structure of molecules at interfaces. In order to obtain this parameter, second order nonlinear spectroscopic techniques including second harmonic gene...The orientation angle is an important parameter that reflects the structure of molecules at interfaces. In order to obtain this parameter, second order nonlinear spectroscopic techniques including second harmonic generation （SHG） and sum frequency generation-vibrational spec- troscopy （SFG-VS） have been successfully applied through analysis of the nonlinear signal from various polarizations. In some SHG and SFG-VS experiments, total internal reflection （TIR） configuration has been adopted to get enhanced signals. However, the reports on the detailed procedure of the polarization analysis and the calculation of the orientation angle of interracial molecules under TIR configuration are still very few. In this paper, we mea- sured the orientation angles of two molecules at the hexadecane-water interface under TIR and Non-TIR experimental configurations. The results measured from polarization analysis in TIR configuration consist with those obtained from Non-TIR configuration. This work demonstrates the feasibility and accuracy of polarization analysis in the determination of the orientation angle of molecules at the interfaces under TIR-SHG configuration.展开更多
In this paper,DOA and subarray-interval estimation are considered and applied to arbitrarily distributed unmanned aerial vehicle(UAV)swarm system,in which multiple small UAVs containing uniform linear array(ULA)are di...In this paper,DOA and subarray-interval estimation are considered and applied to arbitrarily distributed unmanned aerial vehicle(UAV)swarm system,in which multiple small UAVs containing uniform linear array(ULA)are divided by unknown intervals because of dynamic moving.Three parameters are taken to indicate the steering vector,namely,the direction of arrivals(DOAs)of target users,the intervals of UAVs,and the orientation angles of UAVs.The orientation angles are first estimated with an auxiliary user and the DOAs are obtained through a search free rooting method,despite the intervals among the UAVs.Afterwards,the intervals among UAVs can also be calculated via exhaustive when the number of target users are no less than three.We further develop a low-complex method to reduce the computational complexity during subarray-interval estimation.The deterministic Cramér-Rao bound(CRB)of the DOA,orientation angle and subarray-interval can be inferred in a closed form.Eventually,numerical instances are cited to verify the research results.展开更多
The effect of pore morphology and regional distribution on liquid diffusion directionality in nonwoven fabrics was investigated in this study.Pore orientation angle(POA) and pore aspect ratio(PAR) were proposed to cha...The effect of pore morphology and regional distribution on liquid diffusion directionality in nonwoven fabrics was investigated in this study.Pore orientation angle(POA) and pore aspect ratio(PAR) were proposed to characterize the pore morphology,and α-region,β-region,and αβ-region were used to describe the characteristics of the pore regional distribution.The directional characteristics of macroscopic diffusion of liquid in nonwoven fabrics were characterized by the indicator of primary diffusion orientation angle(PDOA).Ten kinds of spunlaced nonwoven fabrics were selected.Firstly,the data of pore characteristic indices of each sample were obtained through scanning electron microscope(SEM) and the image processing technology as well,and the pore regional distribution map of each sample was further acquired.Then,the PDOA of each sample was obtained through the droplet method and image processing technology.Based on the data and statistical analysis,it was found that the PDOA of a certain volume of liquid in the nonwoven fabrics presented a significant linear relationship with the average POA of the nonwoven fabrics.And the characteristics of pore distribution affected the directionality of liquid diffusion in the nonwoven fabrics.The samples with a large proportion of α-region and good distribution had prominent liquid diffusion along the direction of laying-up,and the difference in liquid diffusion of the samples was more obvious between the directions of laying-up and vertical laying-up.展开更多
This paper presents a study on the concur- rent topology optimization of a structure and its material microstructure. A modified optimization model is proposed by introducing microstructure orientation angles as a new...This paper presents a study on the concur- rent topology optimization of a structure and its material microstructure. A modified optimization model is proposed by introducing microstructure orientation angles as a new type of design variable. The new model is based on the assumptions that a structure is made of a material with the same microstructure, and the material may have a different orientation within the design domain of the structure. The homogenization theory is applied to link the material and structure scales. An additional post-processing technique is developed for modifying the obtained design to avoid local optima caused by the use of orientation angle variables. Numerical examples are presented to illustrate the viabil- ity and effectiveness of the proposed model. It is found that significant improvement in structural performance can be achieved by optimizing the orientation of microstructures in concurrent topology optimization of structures and materials.展开更多
Over recent years, Convolutional Neural Networks (CNN) has improved performance on practically every image-based task, including Content-Based Image Retrieval (CBIR). Nevertheless, since features of CNN have altered o...Over recent years, Convolutional Neural Networks (CNN) has improved performance on practically every image-based task, including Content-Based Image Retrieval (CBIR). Nevertheless, since features of CNN have altered orientation, training a CBIR system to detect and correct the angle is complex. While it is possible to construct rotation-invariant features by hand, retrieval accuracy will be low because hand engineering only creates low-level features, while deep learning methods build high-level and low-level features simultaneously. This paper presents a novel approach that combines a deep learning orientation angle detection model with the CBIR feature extraction model to correct the rotation angle of any image. This offers a unique construction of a rotation-invariant CBIR system that handles the CNN features that are not rotation invariant. This research also proposes a further study on how a rotation-invariant deep CBIR can recover images from the dataset in real-time. The final results of this system show significant improvement as compared to a default CNN feature extraction model without the OAD.展开更多
A simplified analytical solution suitable for simple stacking sequences was developed using the Euler buck- ling theory, the structure＇s equations of equilibrium and laminate panel mathematical formulation. Comparing...A simplified analytical solution suitable for simple stacking sequences was developed using the Euler buck- ling theory, the structure＇s equations of equilibrium and laminate panel mathematical formulation. Comparing these results with numerical results reveals the accuracy of the method and even more, allows us to validate the nu- merical analysis. Therefore, two important results are obtained： a simplified analytical solution for the buckling problem and validation of the numerical results. Another important and novel finding is related to the influence of the angle ply orientation and of the cutouts, on the buckling load. Under symmetrical boundary conditions and loading case, rectangular panels with elliptical cutouts, give better results for 90~ oriented plies than for 0 oriented ones. With a compression load applied in the X direction, and with material properties 10 times better in X direction than in Y direction, the best results are obtained when the load is aligned with the Y direction associated to the ma- terial reference frame. Moreover, panels with cutouts seem to behave better than panels without cutouts under cer- tainply orientation angles.展开更多
Surfactants tend to adsorb on the surface/interface mostly in a directional manner.The alkyl chain orientation and conformation order for molecular monolayers of sodium dodecylbenzenesulfonate(SDBS)at low concentratio...Surfactants tend to adsorb on the surface/interface mostly in a directional manner.The alkyl chain orientation and conformation order for molecular monolayers of sodium dodecylbenzenesulfonate(SDBS)at low concentrations are studied by using the sum frequency generation vibrational spectroscopy(SFG-VS).The molecular arrangement of the surfactants adsorbed at the solid/liquid interface is further investigated.It is found that the arrangement of the SDBS at the interface becomes relatively ordered with increasing bulk concentration.Meanwhile,the orientation angle reduces gradually,and the molecules tend to be upright state.In addition,the effect of friction on the conformation order and orientation angle are also analyzed.The intensity of the SDBS vibrational contraction peak becomes lower after friction,which indicates that the anion has a reorientation process at the interface.The arrangement of molecules becomes more disordered due to friction.The orientation angle increases slightly,which indicates the monolayer has an inclined trend relative to the lateral direction on the interface.A modified adsorption model considering friction effect is proposed.This work may provide a reference for the further study of adsorption mechanism and application of surfactants.展开更多
Fiber-reinforced composite materials have excellent specific stiffness,specific strength,and other properties,and have been increasingly widely used in the field of advanced structures.However,the design space dimensi...Fiber-reinforced composite materials have excellent specific stiffness,specific strength,and other properties,and have been increasingly widely used in the field of advanced structures.However,the design space dimensions of fiber-reinforced composite materials will expand explosively,bringing challenges to the efficient analysis and optimal design of structures.In this paper,the authors propose an explicit topology optimization method based on the moving morphable components for designing the fiber-reinforced material.We constrain the intersection area between components to guarantee the independence of each component and avoid the situation that one component is cut by other components.Adding the fiber orientation angle as a design variable,the method can optimize the structural layout and the fiber orientation angle concurrently under the given number of fiber layers and layer thickness.We use two classical examples to verify the feasibility and accuracy of the proposed method.The optimized results are in good agreement with the designs obtained by the 99-line code.The authors also popularize the proposed method to engineering structure.The results manifest that the proposed method has great value in engineering application.展开更多
The damage critical curved surface is derived by considering the related effect of isotropic damage and degradation of cohesion and internal friction angle of Mohr-Coulomb strength law.The characteristics of stress-di...The damage critical curved surface is derived by considering the related effect of isotropic damage and degradation of cohesion and internal friction angle of Mohr-Coulomb strength law.The characteristics of stress-displacement curve and networks of shear bands with the change of degree of damage,confining pressure and Poisson's ratio are investigated numerically by monitoring the stress-displacement values in the process of deformation of samples under plane strain and different initial conditions.The dependence of elastic-plastic response of localization is discussed.The non-uniqueness of the solution of equation is given.The orientation angle of shear band is derived by considering the related effect of isotropic damage and degradation of cohesion and internal friction angle.The orientation angle of shear band obtained by numerical simulation is contrasted to the orientation angle by measuring Mohr circle.It is shown that peak strength and residual strength depend on confining pressure.The networks of shear bands begin to appear in phaseⅡof elasticity and develop in soften phase,and the shear band is formed in the phase of residual strength.As the degree of damage increases,axial displacement at the points of bifurcation and shear band decreases.The orientation angle of shear band increases with the increase of the damage degree.The orientation angle of shear band obtained by numerical simulation and measuring Mohr circle is not much difference when the damage degree is equivalent.The Mohr-Coulomb theory may predict the localized instability of sample by considering the degradation of cohesion and internal friction angle.展开更多
The preferred orientation of pyrolytic carbon coating is an important performance parameter for the safe use of artificial mechanical heart valve.In this paper,the selected area electron diffraction(SAED)analysis of p...The preferred orientation of pyrolytic carbon coating is an important performance parameter for the safe use of artificial mechanical heart valve.In this paper,the selected area electron diffraction(SAED)analysis of pyrolytic carbon coating samples of artificial heart valve was carried out by transmission electron microscopy(TEM),and the experimental method of characterizing the preferred orientation of pyrolytic carbon by electron diffraction spectrum,namely bacon anisotropy factor(BAF),was described,and the orientation angle and BAF corresponding to the electron diffraction spectrum were measured.The results show that the BAF value can directly reflect the anisotropy of pyrolytic carbon in the selected area.The BAF value range is from 1 to infinity,and the higher the preferred orientation is,the greater the value is.The BAF value decreases exponentially with the increase of orientation angle.When the pyrolytic carbon tends to be isotropic,the orientation angle tends to 180 and the BAF value tends to 1.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.52074246)。
文摘The propagation mechanism of microcracks in nanocrystalline single crystal systems under uniaxial dynamic and static tension is investigated using the phase-field-crystal method.Both dynamic and static stretching results show that different orientation angles can induce the crack propagation mode,microscopic morphology,the free energy,crack area change,and causing fracture failure.Crack propagation mode depends on the dislocation activity near the crack tip.Brittle propagation of the crack occurs due to dislocation always at crack tip.Dislocation is emitted at the front end of the crack tip and plastic deformation occurs,which belongs to ductile propagation.The orientation angles of 9°and 14°are brittleductile mixed propagation,while the orientation angles of 19°and 30°are brittle propagation and no dislocation is formed under dynamic tension.The vacancy and vacancy connectivity phenomenon would appear when the orientation angle is14°under static tension,and the crack would be ductile propagation.While the orientation angle is 19°and 30°,the crack propagates in a certain direction,which is a kind of brittle propagation.This work has some practical significance in preventing material fracture failure and improving material performance.
基金supported by the National Science Fund for Distinguished Young Scholars(10925212)the National Natural Science Foundation of China(11002113)the National Basic Research Program of China(2011CB610304)
文摘Orientation optimization plays an important role in the lay-up design of composite structures.Earlier orientation optimization methods face the main problem of huge number of design variables.Recently,a patch concept is proposed to reduce the number of design variables.However,the traditional stress-based method can not deal with patch orientation optimization of composite structures.In this paper,we propose an extended stress-based method to deal with such problems.The considered problems are to minimize the mean compliance under multiple load cases or to maximize the eigenvalues of a composite structure.Four numerical examples are solved to demonstrate the efficiency of the new method.It is shown that the new method has the ability to deal with constraints on orientation angle,such as symmetric,antisymmetric and discrete orientation angle constraints.The iteration is less time-consuming because no sensitivity analysis is needed and a quick convergence rate can be achieved.
基金Project(2012CB957702) supported by the National Basic Research Program of ChinaProjects(41590854,41431070,41274024,41321063) supported by the National Natural Science Foundation of ChinaProject(Y205771077) supported by the Hundred Talents Program of the Chinese Academy of Sciences
文摘The scattering-model-based(SMB)speckle filtering for polarimetric SAR(Pol SAR)data is reasonably effective in preserving dominant scattering mechanisms.However,the efficiency strongly depends on the accuracies of both the decomposition and classification of the scattering properties.In addition,a relatively weak speckle reduction particularly in distributed media was reported in the related literatures.In this work,an improved SMB filtering strategy is proposed considering the aforementioned deficiencies.First,the orientation angle compensation is incorporated into the SMB filtering process to remedy the overestimation of the volume scattering contribution in the Freeman-Durden decomposition.In addition,an algorithm to select the homogenous pixels is developed based on the spatial majority rule for adaptive speckle reduction.We demonstrate the superiority of the proposed methods in terms of scattering property preservation and speckle noise reduction using L-band Pol SAR data sets of San Francisco that were acquired by the NASA/JPL airborne SAR(AIRSAR)system.
文摘The orientation angle is an important parameter that reflects the structure of molecules at interfaces. In order to obtain this parameter, second order nonlinear spectroscopic techniques including second harmonic generation （SHG） and sum frequency generation-vibrational spec- troscopy （SFG-VS） have been successfully applied through analysis of the nonlinear signal from various polarizations. In some SHG and SFG-VS experiments, total internal reflection （TIR） configuration has been adopted to get enhanced signals. However, the reports on the detailed procedure of the polarization analysis and the calculation of the orientation angle of interracial molecules under TIR configuration are still very few. In this paper, we mea- sured the orientation angles of two molecules at the hexadecane-water interface under TIR and Non-TIR experimental configurations. The results measured from polarization analysis in TIR configuration consist with those obtained from Non-TIR configuration. This work demonstrates the feasibility and accuracy of polarization analysis in the determination of the orientation angle of molecules at the interfaces under TIR-SHG configuration.
基金supported by National Natural Science Foundation of China(No.62101601)。
文摘In this paper,DOA and subarray-interval estimation are considered and applied to arbitrarily distributed unmanned aerial vehicle(UAV)swarm system,in which multiple small UAVs containing uniform linear array(ULA)are divided by unknown intervals because of dynamic moving.Three parameters are taken to indicate the steering vector,namely,the direction of arrivals(DOAs)of target users,the intervals of UAVs,and the orientation angles of UAVs.The orientation angles are first estimated with an auxiliary user and the DOAs are obtained through a search free rooting method,despite the intervals among the UAVs.Afterwards,the intervals among UAVs can also be calculated via exhaustive when the number of target users are no less than three.We further develop a low-complex method to reduce the computational complexity during subarray-interval estimation.The deterministic Cramér-Rao bound(CRB)of the DOA,orientation angle and subarray-interval can be inferred in a closed form.Eventually,numerical instances are cited to verify the research results.
基金National Key R&D Program of China (No. 2017YFB0309100)。
文摘The effect of pore morphology and regional distribution on liquid diffusion directionality in nonwoven fabrics was investigated in this study.Pore orientation angle(POA) and pore aspect ratio(PAR) were proposed to characterize the pore morphology,and α-region,β-region,and αβ-region were used to describe the characteristics of the pore regional distribution.The directional characteristics of macroscopic diffusion of liquid in nonwoven fabrics were characterized by the indicator of primary diffusion orientation angle(PDOA).Ten kinds of spunlaced nonwoven fabrics were selected.Firstly,the data of pore characteristic indices of each sample were obtained through scanning electron microscope(SEM) and the image processing technology as well,and the pore regional distribution map of each sample was further acquired.Then,the PDOA of each sample was obtained through the droplet method and image processing technology.Based on the data and statistical analysis,it was found that the PDOA of a certain volume of liquid in the nonwoven fabrics presented a significant linear relationship with the average POA of the nonwoven fabrics.And the characteristics of pore distribution affected the directionality of liquid diffusion in the nonwoven fabrics.The samples with a large proportion of α-region and good distribution had prominent liquid diffusion along the direction of laying-up,and the difference in liquid diffusion of the samples was more obvious between the directions of laying-up and vertical laying-up.
基金supported by the State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, China (Grant GZ1305)
文摘This paper presents a study on the concur- rent topology optimization of a structure and its material microstructure. A modified optimization model is proposed by introducing microstructure orientation angles as a new type of design variable. The new model is based on the assumptions that a structure is made of a material with the same microstructure, and the material may have a different orientation within the design domain of the structure. The homogenization theory is applied to link the material and structure scales. An additional post-processing technique is developed for modifying the obtained design to avoid local optima caused by the use of orientation angle variables. Numerical examples are presented to illustrate the viabil- ity and effectiveness of the proposed model. It is found that significant improvement in structural performance can be achieved by optimizing the orientation of microstructures in concurrent topology optimization of structures and materials.
文摘Over recent years, Convolutional Neural Networks (CNN) has improved performance on practically every image-based task, including Content-Based Image Retrieval (CBIR). Nevertheless, since features of CNN have altered orientation, training a CBIR system to detect and correct the angle is complex. While it is possible to construct rotation-invariant features by hand, retrieval accuracy will be low because hand engineering only creates low-level features, while deep learning methods build high-level and low-level features simultaneously. This paper presents a novel approach that combines a deep learning orientation angle detection model with the CBIR feature extraction model to correct the rotation angle of any image. This offers a unique construction of a rotation-invariant CBIR system that handles the CNN features that are not rotation invariant. This research also proposes a further study on how a rotation-invariant deep CBIR can recover images from the dataset in real-time. The final results of this system show significant improvement as compared to a default CNN feature extraction model without the OAD.
文摘A simplified analytical solution suitable for simple stacking sequences was developed using the Euler buck- ling theory, the structure＇s equations of equilibrium and laminate panel mathematical formulation. Comparing these results with numerical results reveals the accuracy of the method and even more, allows us to validate the nu- merical analysis. Therefore, two important results are obtained： a simplified analytical solution for the buckling problem and validation of the numerical results. Another important and novel finding is related to the influence of the angle ply orientation and of the cutouts, on the buckling load. Under symmetrical boundary conditions and loading case, rectangular panels with elliptical cutouts, give better results for 90~ oriented plies than for 0 oriented ones. With a compression load applied in the X direction, and with material properties 10 times better in X direction than in Y direction, the best results are obtained when the load is aligned with the Y direction associated to the ma- terial reference frame. Moreover, panels with cutouts seem to behave better than panels without cutouts under cer- tainply orientation angles.
基金The work was financially supported by the National Natural Science Foundation of China(Nos.51675297 and 51527901).
文摘Surfactants tend to adsorb on the surface/interface mostly in a directional manner.The alkyl chain orientation and conformation order for molecular monolayers of sodium dodecylbenzenesulfonate(SDBS)at low concentrations are studied by using the sum frequency generation vibrational spectroscopy(SFG-VS).The molecular arrangement of the surfactants adsorbed at the solid/liquid interface is further investigated.It is found that the arrangement of the SDBS at the interface becomes relatively ordered with increasing bulk concentration.Meanwhile,the orientation angle reduces gradually,and the molecules tend to be upright state.In addition,the effect of friction on the conformation order and orientation angle are also analyzed.The intensity of the SDBS vibrational contraction peak becomes lower after friction,which indicates that the anion has a reorientation process at the interface.The arrangement of molecules becomes more disordered due to friction.The orientation angle increases slightly,which indicates the monolayer has an inclined trend relative to the lateral direction on the interface.A modified adsorption model considering friction effect is proposed.This work may provide a reference for the further study of adsorption mechanism and application of surfactants.
基金supports from the National Key Research and Development Plan(2020YFB1709401)the National Natural Science Foundation of China(11872138,11702048),Dalian Young TechStar Project(2019RQ045,2019RQ069)and the Scientific Research Fund Project of Education Department of Liaoning Province(JDL2020021).
文摘Fiber-reinforced composite materials have excellent specific stiffness,specific strength,and other properties,and have been increasingly widely used in the field of advanced structures.However,the design space dimensions of fiber-reinforced composite materials will expand explosively,bringing challenges to the efficient analysis and optimal design of structures.In this paper,the authors propose an explicit topology optimization method based on the moving morphable components for designing the fiber-reinforced material.We constrain the intersection area between components to guarantee the independence of each component and avoid the situation that one component is cut by other components.Adding the fiber orientation angle as a design variable,the method can optimize the structural layout and the fiber orientation angle concurrently under the given number of fiber layers and layer thickness.We use two classical examples to verify the feasibility and accuracy of the proposed method.The optimized results are in good agreement with the designs obtained by the 99-line code.The authors also popularize the proposed method to engineering structure.The results manifest that the proposed method has great value in engineering application.
基金the National Natural Science Foundation of China(No.51009015)the Education Foundation of Liaoning(No.L2010038)
文摘The damage critical curved surface is derived by considering the related effect of isotropic damage and degradation of cohesion and internal friction angle of Mohr-Coulomb strength law.The characteristics of stress-displacement curve and networks of shear bands with the change of degree of damage,confining pressure and Poisson's ratio are investigated numerically by monitoring the stress-displacement values in the process of deformation of samples under plane strain and different initial conditions.The dependence of elastic-plastic response of localization is discussed.The non-uniqueness of the solution of equation is given.The orientation angle of shear band is derived by considering the related effect of isotropic damage and degradation of cohesion and internal friction angle.The orientation angle of shear band obtained by numerical simulation is contrasted to the orientation angle by measuring Mohr circle.It is shown that peak strength and residual strength depend on confining pressure.The networks of shear bands begin to appear in phaseⅡof elasticity and develop in soften phase,and the shear band is formed in the phase of residual strength.As the degree of damage increases,axial displacement at the points of bifurcation and shear band decreases.The orientation angle of shear band increases with the increase of the damage degree.The orientation angle of shear band obtained by numerical simulation and measuring Mohr circle is not much difference when the damage degree is equivalent.The Mohr-Coulomb theory may predict the localized instability of sample by considering the degradation of cohesion and internal friction angle.
文摘The preferred orientation of pyrolytic carbon coating is an important performance parameter for the safe use of artificial mechanical heart valve.In this paper,the selected area electron diffraction(SAED)analysis of pyrolytic carbon coating samples of artificial heart valve was carried out by transmission electron microscopy(TEM),and the experimental method of characterizing the preferred orientation of pyrolytic carbon by electron diffraction spectrum,namely bacon anisotropy factor(BAF),was described,and the orientation angle and BAF corresponding to the electron diffraction spectrum were measured.The results show that the BAF value can directly reflect the anisotropy of pyrolytic carbon in the selected area.The BAF value range is from 1 to infinity,and the higher the preferred orientation is,the greater the value is.The BAF value decreases exponentially with the increase of orientation angle.When the pyrolytic carbon tends to be isotropic,the orientation angle tends to 180 and the BAF value tends to 1.
