Strain hardening in austenitic stainless steels is modeled according to an internal state variable constitutive model. Derivation of model constants from published stress-strain curves over a range of test temperature...Strain hardening in austenitic stainless steels is modeled according to an internal state variable constitutive model. Derivation of model constants from published stress-strain curves over a range of test temperatures and strain rates is reviewed. Model constants for this material system published previously are revised to make them more consistent with model constants in other material systems.展开更多
As a model bee metal, tantalum and its alloys have wide applications in defense-related fields. The KHL （Khan, Huang, Liang, 1999） model and the constitutive model proposed by Nemat-Nasser et al （Nemat-Nasser and K...As a model bee metal, tantalum and its alloys have wide applications in defense-related fields. The KHL （Khan, Huang, Liang, 1999） model and the constitutive model proposed by Nemat-Nasser et al （Nemat-Nasser and Kapoor, 2001） for tantalum and its alloys were analyzed and compared with each other. A set of published data recorded during elastic-plastic deformations of tantalum, tantalum alloy containing tungsten of 2.5% （Ta-2.5W）, over a wide range of strains, strain rates, and temperatures were used to correlate the two models. Overall, it can be concluded that KHL model correlates much better with the data than the model used by Nemat-Nasser et al.展开更多
The nano-carbon powders are often used as fillers to endow the shape memory polymers(SMPs)with electroconductivity.It has been found that the shape memory effects(SMEs)of SMPs filled with nano-carbon powder can be tri...The nano-carbon powders are often used as fillers to endow the shape memory polymers(SMPs)with electroconductivity.It has been found that the shape memory effects(SMEs)of SMPs filled with nano-carbon powder can be triggered both by temperature and by water.To reveal the driving mechanism of SMEs,a constitutive model for describing the thermally activated and moisture activated SMEs of these shape memory polymer composite(SMPCs)is developed here.Because both of the SMEs share the same driving mechanism,the variable moisture is incorporated into the framework of a thermo-mechanical modeling approach to disclose the effect of moisture on the thermoviscoelastic properties.The SMPCs are regarded as isotropic materials and the effect of carbon powder on the mechanical properties of the matrix is also considered in the paper.Because the complete recovery may not be reached even they are exposed to the stimulus environment long enough,the blocking mechanism is also considered here.This is the mainly new contribution compared to the early work.Using the method of parameter determination presented here,the effectiveness of the proposed hygro-thermo-mechanical constitutive model is confirmed by comparing the model results with the test data of uniaxial deformation from the literature.展开更多
Previous constitutive models of granite shear creep have two limitations：（1） although moisture greatly affects granite shear creep behavior, currently there are no constitutive models that include this factor;（2）...Previous constitutive models of granite shear creep have two limitations：（1） although moisture greatly affects granite shear creep behavior, currently there are no constitutive models that include this factor;（2） there are also no models that include an acceleration stage. This paper presents an improved Burgers constitutive model with the addition of a damage parameter to characterize the moisture effect and uses a nonlinear relation equation between stress and strain for inclusion as the acceleration stage. The damage parameter is determined from granite creep experiment under four different moisture contents（0%, 0.22%, 0.49%, and 0.79%）. The nonlinear relation equation is obtained by fitting a dataset of stain versus time under five different loading stages. To verify the presented model, a creep experiment was conducted on other granite samples and the results show that the model agrees well with the experimental observation data.展开更多
An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model （original B-P） to improve the modeling of rate-dependent plasticity and cyclic hardening beha...An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model （original B-P） to improve the modeling of rate-dependent plasticity and cyclic hardening behaviors of metals. The extended model （new B-P） contains two isotropic internal variables： one plays the role of representing the fast hardening in smaller inelastic strain range, while the other evolutes at slower speed accompanied by larger accumulated inelastic deformation, such as cyclic hardening. To examine the validity of the extended constitutive model, the rate-dependent plasticity of a Ni-base superalloy Udimet 720Li at 650℃ and 700℃ are characterized using both models. Not only numerical simulations are conducted for various loading conditions by implementing both models into ABAOUS using a user material subroutine, also a systematic comparison between two models is completed. Numerical results show that the extended material constants in the new model provide more flexible capability in modeling the inelastic behavior of the material with sound accuracy.展开更多
文摘Strain hardening in austenitic stainless steels is modeled according to an internal state variable constitutive model. Derivation of model constants from published stress-strain curves over a range of test temperatures and strain rates is reviewed. Model constants for this material system published previously are revised to make them more consistent with model constants in other material systems.
文摘As a model bee metal, tantalum and its alloys have wide applications in defense-related fields. The KHL （Khan, Huang, Liang, 1999） model and the constitutive model proposed by Nemat-Nasser et al （Nemat-Nasser and Kapoor, 2001） for tantalum and its alloys were analyzed and compared with each other. A set of published data recorded during elastic-plastic deformations of tantalum, tantalum alloy containing tungsten of 2.5% （Ta-2.5W）, over a wide range of strains, strain rates, and temperatures were used to correlate the two models. Overall, it can be concluded that KHL model correlates much better with the data than the model used by Nemat-Nasser et al.
基金This work was supported by the Natural Science Foundation of Jiangsu Province[BK20170759].
文摘The nano-carbon powders are often used as fillers to endow the shape memory polymers(SMPs)with electroconductivity.It has been found that the shape memory effects(SMEs)of SMPs filled with nano-carbon powder can be triggered both by temperature and by water.To reveal the driving mechanism of SMEs,a constitutive model for describing the thermally activated and moisture activated SMEs of these shape memory polymer composite(SMPCs)is developed here.Because both of the SMEs share the same driving mechanism,the variable moisture is incorporated into the framework of a thermo-mechanical modeling approach to disclose the effect of moisture on the thermoviscoelastic properties.The SMPCs are regarded as isotropic materials and the effect of carbon powder on the mechanical properties of the matrix is also considered in the paper.Because the complete recovery may not be reached even they are exposed to the stimulus environment long enough,the blocking mechanism is also considered here.This is the mainly new contribution compared to the early work.Using the method of parameter determination presented here,the effectiveness of the proposed hygro-thermo-mechanical constitutive model is confirmed by comparing the model results with the test data of uniaxial deformation from the literature.
基金supported by the National Natural Science Foundation of China (No. 41172281)the National Basic Research Program of China (No. 2011CB710604)the Opening Foundation of the State Key Laboratory of Continental Dynamics, Northwest University (No. 201210126)
文摘Previous constitutive models of granite shear creep have two limitations：（1） although moisture greatly affects granite shear creep behavior, currently there are no constitutive models that include this factor;（2） there are also no models that include an acceleration stage. This paper presents an improved Burgers constitutive model with the addition of a damage parameter to characterize the moisture effect and uses a nonlinear relation equation between stress and strain for inclusion as the acceleration stage. The damage parameter is determined from granite creep experiment under four different moisture contents（0%, 0.22%, 0.49%, and 0.79%）. The nonlinear relation equation is obtained by fitting a dataset of stain versus time under five different loading stages. To verify the presented model, a creep experiment was conducted on other granite samples and the results show that the model agrees well with the experimental observation data.
文摘An additional isotropic internal variable is utilized to extend the Bodner-Partom unified viscoplastic constitutive model （original B-P） to improve the modeling of rate-dependent plasticity and cyclic hardening behaviors of metals. The extended model （new B-P） contains two isotropic internal variables： one plays the role of representing the fast hardening in smaller inelastic strain range, while the other evolutes at slower speed accompanied by larger accumulated inelastic deformation, such as cyclic hardening. To examine the validity of the extended constitutive model, the rate-dependent plasticity of a Ni-base superalloy Udimet 720Li at 650℃ and 700℃ are characterized using both models. Not only numerical simulations are conducted for various loading conditions by implementing both models into ABAOUS using a user material subroutine, also a systematic comparison between two models is completed. Numerical results show that the extended material constants in the new model provide more flexible capability in modeling the inelastic behavior of the material with sound accuracy.
