The natural clayey soils are usually structural and unsaturated,which makes their mechanical properties quite different from the remolded saturated soils.A structural constitutive model is proposed to simulate the bon...The natural clayey soils are usually structural and unsaturated,which makes their mechanical properties quite different from the remolded saturated soils.A structural constitutive model is proposed to simulate the bonding-breakage micro-mechanism.In this model,the unsaturated soil element is divided into a cementation element and a friction element according to the binary medium theory,and the stress-strain coordination for these two elements is obtained. The cementation element is regarded as elastic,whereas the friction element is regarded as elastoplastic which can be described with the Gallipoli＇s model.The theoretical formulation is verified with the comparative experiments of isotropic compressions on the saturated and unsaturated structural soils.Parametric analyses of the effects of damage variables on the model predictions are further carried out,which show that breakage deformation of natural clayey soils increases with the rising amount of initial defects.展开更多
A constitutive model for methane hydrate-bearing sediment(MHBS)is essential for the analysis of mechanical response of MHBS to the change of hydrate saturation caused by gas extraction. A new elasto-plastic constituti...A constitutive model for methane hydrate-bearing sediment(MHBS)is essential for the analysis of mechanical response of MHBS to the change of hydrate saturation caused by gas extraction. A new elasto-plastic constitutive model is built in order to simulate the mechanical behavior of MHBS in this paper. This model represents more significant mechanical properties of MHBS such as bonding, higher stiffness, softening and stress-strain nonlinear relationship. The bonding behavior can be described by use of a parameter related to mechanical hydrate saturation. Higher stiffness can be modeled by the introduction of hydrate saturation into traditional expression of soil stiffness. Softening can be controlled by a function describing the relationship between cohesion and bonding structure factor. Dilatancy can be estimated by establishing the relationship between the lateral strain and axial strain. Meanwhile, the hypothesis of isotropic expanding is applied to the calculation of the volumetric strain. The stress-strain curves under different hydrate saturation conditions predicted by the proposed model are in good agreement with the test data. All the coefficients can be easily obtained by the triaxial test of MHBS.展开更多
To establish bonding stress—slip constitutive model between bars and grout concrete,13 test specimens were employed to study the bonding behavior and the force transfer of bars adhered to grout concrete. The bonding ...To establish bonding stress—slip constitutive model between bars and grout concrete,13 test specimens were employed to study the bonding behavior and the force transfer of bars adhered to grout concrete. The bonding stress development of bars adhered to grout concrete was analyzed. The local bonding stress—slip curve was obtained. Based on the test results,a new bonding stress— slip constitutive model between bars and grout concrete was proposed. The results show that the maximum bonding stress is not influenced by the bar bond length,but it is strengthened when the splitting strength of grout concrete is increased. The model matches the experimental results well,and the regressing coefficient equals 1.7.展开更多
Ten specimens were tested in this paper in order to study the bond behavior and the process of force transfer when bars adhered to mortar. The development of the bond stress between bars and mortar was calculated. Tes...Ten specimens were tested in this paper in order to study the bond behavior and the process of force transfer when bars adhered to mortar. The development of the bond stress between bars and mortar was calculated. Test results show that the maximum bond-stress is not influenced by the bar bond length and increases as the increased splitting strength of mortar for block. The local bond stress-slip curve was obtained. Then,based on the regressive analysis of test data,two bond shearing stress-slip constitutive models between bars and mortar were proposed. The models can be used in the numerical simulation or finite element analysis and provide references for the improvement of the corresponding design codes.展开更多
In this work,two-stage diffusion bonding of micro-duplex TC4 titanium alloy was car-ried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling du...In this work,two-stage diffusion bonding of micro-duplex TC4 titanium alloy was car-ried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling during the hot forming process.Microstructure and mechanical properties test were used to verify the good quality of the equiaxed fine grain diffusion-welded TC4 alloy.Quasi-static tensile experiment was carried out at temperatures ranging from 750–900℃and strain rates of 0.0001–0.1 s^(-1).The joint showed the weak dynamic recovery at strain rates of 0.01–0.1 s^(-1)and temperatures of 750–850℃.At strain rates of 0.0001–0.001 s^(-1)and tempera-tures of 850–900℃,the flow stress of joint presented steady-state characteristics.Different defor-mation conditions lead to the remarkable difference of dynamic softening performance between the joint and heat-treated base metal,but the flow stress in elastic and strain hardening stages exhibited similar behavior.The strain compensated Arrhenius-type constitutive models of TC4 joint and heat-treated base metal were developed respectively.The fifth-order polynomial functions between the material property correlation coefficients and strain were obtained.The models have shown good correlation,with correlation coefficient values of 0.984 and 0.99.The percentage average absolute relative error for the models were found to be 10%and 9.46%,respectively.展开更多
To effectively simulate the fracture propagation in shale,the bedding plane(BP)effect is incorporated into the augmented virtual internal bond(AVIB)constitutive relation through BP tensor.Comparing the BP-embedded AVI...To effectively simulate the fracture propagation in shale,the bedding plane(BP)effect is incorporated into the augmented virtual internal bond(AVIB)constitutive relation through BP tensor.Comparing the BP-embedded AVIB with the theory of transverse isotropy,it is found the approach can represent the anisotropic properties induced by parallel BPs.Through the simulation example,it is found that this method can simulate the stiffness anisotropy of shale and can represent the effect of BPs on hydraulic fracture propagation direction.Compared with the BP-embedded virtual internal bond(VIB),this method can account for the various Poisson’s ratio.It provides a feasible approach to simulate the fracture propagation in shale.展开更多
基金supported by the National Natural Science Foundation of China(50778013)the National Basic Research Program of China(973 Program)(2010CB732100)Beijing Municipal Natural Science Foundation(8082020).
文摘The natural clayey soils are usually structural and unsaturated,which makes their mechanical properties quite different from the remolded saturated soils.A structural constitutive model is proposed to simulate the bonding-breakage micro-mechanism.In this model,the unsaturated soil element is divided into a cementation element and a friction element according to the binary medium theory,and the stress-strain coordination for these two elements is obtained. The cementation element is regarded as elastic,whereas the friction element is regarded as elastoplastic which can be described with the Gallipoli＇s model.The theoretical formulation is verified with the comparative experiments of isotropic compressions on the saturated and unsaturated structural soils.Parametric analyses of the effects of damage variables on the model predictions are further carried out,which show that breakage deformation of natural clayey soils increases with the rising amount of initial defects.
基金Supported by the National Science and Technology Major Project of China(No.2011ZX05026-004)the National Natural Science Foundation of China(No.51309047 and No.51509032)
文摘A constitutive model for methane hydrate-bearing sediment(MHBS)is essential for the analysis of mechanical response of MHBS to the change of hydrate saturation caused by gas extraction. A new elasto-plastic constitutive model is built in order to simulate the mechanical behavior of MHBS in this paper. This model represents more significant mechanical properties of MHBS such as bonding, higher stiffness, softening and stress-strain nonlinear relationship. The bonding behavior can be described by use of a parameter related to mechanical hydrate saturation. Higher stiffness can be modeled by the introduction of hydrate saturation into traditional expression of soil stiffness. Softening can be controlled by a function describing the relationship between cohesion and bonding structure factor. Dilatancy can be estimated by establishing the relationship between the lateral strain and axial strain. Meanwhile, the hypothesis of isotropic expanding is applied to the calculation of the volumetric strain. The stress-strain curves under different hydrate saturation conditions predicted by the proposed model are in good agreement with the test data. All the coefficients can be easily obtained by the triaxial test of MHBS.
基金Project(2006BAJ03A01-05) supported by National Science and Technology Pillar Program during the 11th Five-Year Plan Period of ChinaProject (JG200705) supported by Key Laboratory of Structural Engineering of Shenyang Jianzhu University, China
文摘To establish bonding stress—slip constitutive model between bars and grout concrete,13 test specimens were employed to study the bonding behavior and the force transfer of bars adhered to grout concrete. The bonding stress development of bars adhered to grout concrete was analyzed. The local bonding stress—slip curve was obtained. Based on the test results,a new bonding stress— slip constitutive model between bars and grout concrete was proposed. The results show that the maximum bonding stress is not influenced by the bar bond length,but it is strengthened when the splitting strength of grout concrete is increased. The model matches the experimental results well,and the regressing coefficient equals 1.7.
基金Sponsored by the National Science and Technology Pillar Program during the 11th Five-Year Plan Period of China(Grant No. 2009BAK58B03-03 and 2006BAJ03A01-05)the Key Laboratory of Structural Engineering of Shenyang Jianzhu University,China(Grant No. JG200705)the Science & Re-search Program of Shenyang,China(Grant No. 1091064-A-00)
文摘Ten specimens were tested in this paper in order to study the bond behavior and the process of force transfer when bars adhered to mortar. The development of the bond stress between bars and mortar was calculated. Test results show that the maximum bond-stress is not influenced by the bar bond length and increases as the increased splitting strength of mortar for block. The local bond stress-slip curve was obtained. Then,based on the regressive analysis of test data,two bond shearing stress-slip constitutive models between bars and mortar were proposed. The models can be used in the numerical simulation or finite element analysis and provide references for the improvement of the corresponding design codes.
基金supported by the National Natural Science Foundation of China(No.51675029).
文摘In this work,two-stage diffusion bonding of micro-duplex TC4 titanium alloy was car-ried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling during the hot forming process.Microstructure and mechanical properties test were used to verify the good quality of the equiaxed fine grain diffusion-welded TC4 alloy.Quasi-static tensile experiment was carried out at temperatures ranging from 750–900℃and strain rates of 0.0001–0.1 s^(-1).The joint showed the weak dynamic recovery at strain rates of 0.01–0.1 s^(-1)and temperatures of 750–850℃.At strain rates of 0.0001–0.001 s^(-1)and tempera-tures of 850–900℃,the flow stress of joint presented steady-state characteristics.Different defor-mation conditions lead to the remarkable difference of dynamic softening performance between the joint and heat-treated base metal,but the flow stress in elastic and strain hardening stages exhibited similar behavior.The strain compensated Arrhenius-type constitutive models of TC4 joint and heat-treated base metal were developed respectively.The fifth-order polynomial functions between the material property correlation coefficients and strain were obtained.The models have shown good correlation,with correlation coefficient values of 0.984 and 0.99.The percentage average absolute relative error for the models were found to be 10%and 9.46%,respectively.
基金This work is supported by the National Natural Science Foundation of China(Grant 11772190),which is gratefully acknowledged.
文摘To effectively simulate the fracture propagation in shale,the bedding plane(BP)effect is incorporated into the augmented virtual internal bond(AVIB)constitutive relation through BP tensor.Comparing the BP-embedded AVIB with the theory of transverse isotropy,it is found the approach can represent the anisotropic properties induced by parallel BPs.Through the simulation example,it is found that this method can simulate the stiffness anisotropy of shale and can represent the effect of BPs on hydraulic fracture propagation direction.Compared with the BP-embedded virtual internal bond(VIB),this method can account for the various Poisson’s ratio.It provides a feasible approach to simulate the fracture propagation in shale.
