Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both t...Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.展开更多
In order to study deposited sediment settlement and consolidation mechanisms, sediment settlement experiments were conducted using a settlement column. Based on the experimental results, sediment settlement stage defi...In order to study deposited sediment settlement and consolidation mechanisms, sediment settlement experiments were conducted using a settlement column. Based on the experimental results, sediment settlement stage definition, excessive pore pressure （EPP） dissipation, and consolidation constitutive equations are discussed. Three stages, including the free settlement, hindered settlement, and self-weight consolidation settlement stages, are defined. The results of this study show that sediment settlement is mainly affected by the initial sediment concentration and initial settlement height, and the interface settlement rate is linearly attenuated with time on bilogarithmic scales during the hindered settlement and self-weight consolidation settlement stages. Moreover, the deposited sediment layer in the self-weight consolidation settlement stage experiences large strains, and the settlement amount in this stage is about 32% to 59% of the initial height of deposited sediment. EPP is nonlinearly distributed in the settlement direction, and consolidation settlement is faster than EPP dissipation in the self-weight consolidation settlement stage. Consolidation constitutive equations for the hydraulic conductivity and effective stress, applicable to large-strain consolidation calculation, were also determined and fitted in the power function form.展开更多
Large-strain deformations introduce several confounding factors that affect the application of the Mechanical Threshold Stress model. These include the decrease with the increasing stress of the normalized activation ...Large-strain deformations introduce several confounding factors that affect the application of the Mechanical Threshold Stress model. These include the decrease with the increasing stress of the normalized activation energy characterizing deformation kinetics, the tendency toward Stage IV hardening at high strains, and the influence of crystallographic texture. Minor additions to the Mechanical Threshold Stress model are introduced to account for variations of the activation energy and the addition of Stage IV hardening. Crystallographic texture cannot be modeled using an isotropic formulation, but some common trends when analyzing predominantly shear deformation followed by uniaxial deformation are described. Comparisons of model predictions with measurements in copper processed using Equal Channel Angular Pressing are described.展开更多
Ionic hydrogels,owing to the advantages of stretchability,conductivity and transparency,have attracted more attention for developing new soft sensors and artificial skins.Existing works on ionic-hydrogel based sensors...Ionic hydrogels,owing to the advantages of stretchability,conductivity and transparency,have attracted more attention for developing new soft sensors and artificial skins.Existing works on ionic-hydrogel based sensors mostly focus on material synthesis,structure design and functional integration,while few studies investigate the characterization of their sensing performances.In this paper,we present a method to characterize the performance(e.g.,sensitivity,linearity and repeatability)of a kind of ionic-hydrogel based strain sensors by varying the testing frequencies and the sensors’geometry(e.g.,length-width(L/W)ratio).To this end,we first develop an experimental testing platform and fabricate a series of strain sensors made of the polyacrylamide(PAAm)hydrogel containing ionic conductive medium.We establish an equivalent electrical model to represent the ionic-hydrogel based strain sensors,indicating the influence of the testing frequencies and L/W ratio of the ionic hydrogels on their sensing performances.These theoretical predictions are in agreement with results obtained through experimental measurements.We further demonstrate that(1)the sensitivity of the strain sensors,characterized by the gauge factor(GF),increases with the rise of testing frequencies but tends to be stable over the frequency of 5 kHz;(2)the sensitivity GF has a nonlinear relation with the L/W ratio of the strain sensors,but with a certain maximum value under the same testing frequency when the L/W ratio equals to 4.80.We verify the above experimental observations with two commonly used electrolytes,including lithium chloride and sodium chloride.With the optimum testing frequency and L/W ratio,we finally conduct various experiments to demonstrate the low hysteresis and good repeatability of our ionic-hydrogel based strain sensors.This work provides an approach to characterize the performance of the ionic-hydrogel based strain sensors,which may be an important step forward in further applications of ionic hydrogels in soft robotics.展开更多
Car manufacturing is always regarded as the key industry behind sheet metal forming, and thus, the requirements of and developments in car manufacturing play a decisive role in the development of sheet metal forming. ...Car manufacturing is always regarded as the key industry behind sheet metal forming, and thus, the requirements of and developments in car manufacturing play a decisive role in the development of sheet metal forming. The automotive industry is faced with contradictory demands and requirements： better performance with lower consumption and less harmful emissions, more safety and comfort; these are extremely difficult to supply simultaneously with conventional materials and conventional manufacturing processes. The fulfillment of these often contradictory requirements is one of the main driving forces in the automotive industry and thus in the material and process developments in sheet metal forming, as well. In recent years, significant developments can be observed in the application of high-strength steels. In this respect, the application of various dual-phase steels is one of the best examples. However, the application of these highstrength steels often leads to formability and manufacturing problems. One formability problem is the springback occurring after sheet metal forming. In the current research, we have dealt mainly with advanced high-strength steels, primarily with dual-phase steels. When applying them, the springback phenomenon is one of the most critical issues. To reduce the tremendous amount of experimental work needed, we also applied numerical simulation using isotropic–kinematic hardening rules. The isotropic–kinematic hardening behavior of a given material in the applied Auto Form numerical package may be characterized with three independent material parameters c, v and K（a detailed explanation of their meaning will be given in the main part of this paper）. However, we found that the material data included in simulation packages for these new high-strength steels are not fully adequate. For the determination of more reliable material parameters and to achieve better simulation results, a new testing device was developed. Numerical simulations were performed using the material parameters determined by the new device to show the sensitivity of springback behavior to these material parameters.展开更多
基金Projects(51109092,11272137)supported by the National Natural Science Foundation of ChinaProjects(2013M530237,2014T70479)supported by China Postdoctoral Science FoundationProject(SJLX15-0498)supported by Jiangsu Provincial Graduate Students Research and Innovation Program,China
文摘Geometrical nonlinearity of the soft soil and the deviation of water flow in the soft clay from Darcy's law have been well recognized in practice. However, the theory of consolidation, which can account for both the geometrical nonlinearity and the non-Darcian flow, has not been reported so far. In this contribution, a model for the consolidation of soft clay which can allow for these two factors simultaneously is proposed. Utilizing the finite difference method, the numerical model for this problem is developed. With the numerical model, the effects of the geometrical nonlinearity and the non-Darcian flow on the consolidation of the soft soil are investigated. The results show that when the self-weight stress is calculated by the same method, the rate of the non-Darcian consolidation for the large-strain case is larger than that for the small-strain case, but the difference between them is limited. However, the difference between the consolidation rates caused by the non-Darcian and Darcian flows is significant. Therefore, when the geometrical nonlinearity of the soft clay is considered in calculating the consolidation settlement, due to the complexity of the large-strain assumption, the small-strain assumption can be used to replace it if the self-weight stress for the small-strain assumption is calculated by considering its sedimentation. However, due to the aforementioned large difference between the consolidation rates with consideration of the non-Darcian flow in soft clay or not, it is better to consider the non-Darcian flow law for both the small and large stain assumptions.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.2009B13514)the Doctoral Fund of the Ministry of Education of China(Grant No.20100094110002)
文摘In order to study deposited sediment settlement and consolidation mechanisms, sediment settlement experiments were conducted using a settlement column. Based on the experimental results, sediment settlement stage definition, excessive pore pressure （EPP） dissipation, and consolidation constitutive equations are discussed. Three stages, including the free settlement, hindered settlement, and self-weight consolidation settlement stages, are defined. The results of this study show that sediment settlement is mainly affected by the initial sediment concentration and initial settlement height, and the interface settlement rate is linearly attenuated with time on bilogarithmic scales during the hindered settlement and self-weight consolidation settlement stages. Moreover, the deposited sediment layer in the self-weight consolidation settlement stage experiences large strains, and the settlement amount in this stage is about 32% to 59% of the initial height of deposited sediment. EPP is nonlinearly distributed in the settlement direction, and consolidation settlement is faster than EPP dissipation in the self-weight consolidation settlement stage. Consolidation constitutive equations for the hydraulic conductivity and effective stress, applicable to large-strain consolidation calculation, were also determined and fitted in the power function form.
文摘Large-strain deformations introduce several confounding factors that affect the application of the Mechanical Threshold Stress model. These include the decrease with the increasing stress of the normalized activation energy characterizing deformation kinetics, the tendency toward Stage IV hardening at high strains, and the influence of crystallographic texture. Minor additions to the Mechanical Threshold Stress model are introduced to account for variations of the activation energy and the addition of Stage IV hardening. Crystallographic texture cannot be modeled using an isotropic formulation, but some common trends when analyzing predominantly shear deformation followed by uniaxial deformation are described. Comparisons of model predictions with measurements in copper processed using Equal Channel Angular Pressing are described.
基金supported by the National Natural Science Foundation of China(Grant Nos.9184820451622506 and 91948302)the Shanghai Jiao Tong University Scientific and Technological Innovation Funds。
文摘Ionic hydrogels,owing to the advantages of stretchability,conductivity and transparency,have attracted more attention for developing new soft sensors and artificial skins.Existing works on ionic-hydrogel based sensors mostly focus on material synthesis,structure design and functional integration,while few studies investigate the characterization of their sensing performances.In this paper,we present a method to characterize the performance(e.g.,sensitivity,linearity and repeatability)of a kind of ionic-hydrogel based strain sensors by varying the testing frequencies and the sensors’geometry(e.g.,length-width(L/W)ratio).To this end,we first develop an experimental testing platform and fabricate a series of strain sensors made of the polyacrylamide(PAAm)hydrogel containing ionic conductive medium.We establish an equivalent electrical model to represent the ionic-hydrogel based strain sensors,indicating the influence of the testing frequencies and L/W ratio of the ionic hydrogels on their sensing performances.These theoretical predictions are in agreement with results obtained through experimental measurements.We further demonstrate that(1)the sensitivity of the strain sensors,characterized by the gauge factor(GF),increases with the rise of testing frequencies but tends to be stable over the frequency of 5 kHz;(2)the sensitivity GF has a nonlinear relation with the L/W ratio of the strain sensors,but with a certain maximum value under the same testing frequency when the L/W ratio equals to 4.80.We verify the above experimental observations with two commonly used electrolytes,including lithium chloride and sodium chloride.With the optimum testing frequency and L/W ratio,we finally conduct various experiments to demonstrate the low hysteresis and good repeatability of our ionic-hydrogel based strain sensors.This work provides an approach to characterize the performance of the ionic-hydrogel based strain sensors,which may be an important step forward in further applications of ionic hydrogels in soft robotics.
基金the New Hungarian Development Plan and jointly financed by the European Union and European Social Fund
文摘Car manufacturing is always regarded as the key industry behind sheet metal forming, and thus, the requirements of and developments in car manufacturing play a decisive role in the development of sheet metal forming. The automotive industry is faced with contradictory demands and requirements： better performance with lower consumption and less harmful emissions, more safety and comfort; these are extremely difficult to supply simultaneously with conventional materials and conventional manufacturing processes. The fulfillment of these often contradictory requirements is one of the main driving forces in the automotive industry and thus in the material and process developments in sheet metal forming, as well. In recent years, significant developments can be observed in the application of high-strength steels. In this respect, the application of various dual-phase steels is one of the best examples. However, the application of these highstrength steels often leads to formability and manufacturing problems. One formability problem is the springback occurring after sheet metal forming. In the current research, we have dealt mainly with advanced high-strength steels, primarily with dual-phase steels. When applying them, the springback phenomenon is one of the most critical issues. To reduce the tremendous amount of experimental work needed, we also applied numerical simulation using isotropic–kinematic hardening rules. The isotropic–kinematic hardening behavior of a given material in the applied Auto Form numerical package may be characterized with three independent material parameters c, v and K（a detailed explanation of their meaning will be given in the main part of this paper）. However, we found that the material data included in simulation packages for these new high-strength steels are not fully adequate. For the determination of more reliable material parameters and to achieve better simulation results, a new testing device was developed. Numerical simulations were performed using the material parameters determined by the new device to show the sensitivity of springback behavior to these material parameters.
