Journal of Engineering Materials and Technology-transactions of The Asme, Aug 4, 2023
Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combi... more Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combinations of temperatures and strain rates. Despite the phenomenon being reported in several other studies, the literature still lacks a specific constitutive model that can physically interpret its effect. Therefore, this work proposes a modification based on physical parameters to the Voyiadjis and Abed (VA) model to account for the effect of DSA in C45 steel. The resulting modified model is then coupled with an energy-based damage model to further capture the effect of material softening. Previously, in VA model, it was assumed that the total activation energy for overcoming the obstacles without external work remains the same which works well in the absence of DSA. However, during DSA, the mobile dislocations are pinned by the diffusing solute atoms. This results in an increase in the total activation free energy needed by the dislocations to overcome the obstacle. Thus, an increase in strength is observed. It is shown in the current work that utilizing the concept of increased solute concentrations at local obstacles, in conjunction with the physical description that the VA model is based upon, successfully captures the phenomenon of DSA in C45 steel. In addition, the metal experiencing softening after reaching its ultimate strength is due to the significant growth of voids and cracks within the microstructure. To capture this behavior, an energy-based damage parameter is incorporated into the proposed model. The coupled plasticity-damage model shows a good comparison with the experimental results.
International Journal for Multiscale Computational Engineering, 2007
ABSTRACT In general, metal structures display a strong rate and temperature dependence when defor... more ABSTRACT In general, metal structures display a strong rate and temperature dependence when deformed nonuniformly into the inelastic range. This effect has important implications for an increasing number of applications in structural and engineering mechanics. The mechanical behavior of these applications cannot be characterized by classical (rate-independent) continuum theories because they incorporate no material length scales. It is therefore necessary to develop a rate-dependent (viscoplasticity) continuum theory bridging the gap between the classical continuum theories and the microstructure simulations. A finite strain hypoelastoviscoplastic framework is developed for body-centered cubic metals using the corotational formulation approach. Material length scales are implicitly introduced into the governing equations through material rate dependency (viscosity). An implicit objective stress update, which is an efficient algorithm for the type of nonlinear problems considered here, is employed. The effectiveness of the present approach is tested by studying strain localizations in a simple tensile plane strain problem and in a cylindrical hat-shaped sample over a wide range of initial temperatures and strain rates. The finite element simulations of material instability problems converge to meaningful results on further refinement of the finite element mesh. Comparisons of the simulation results of adiabatic shear localizations are also made, with experimental results conducted by different authors. Results indicate an excellent performance of the present framework in describing the strain localization problem for niobium, vanadium, and tantalum.
Mechanics of Time-dependent Materials, Mar 11, 2010
... inconsistencies, in fact, are attributed to certain assumptions used in the ZA model formulat... more ... inconsistencies, in fact, are attributed to certain assumptions used in the ZA model formulation that cause the model parameters to be inaccurately re-lated to the microstructural physical quantities (see, for more details, Abed and Voyiadjis 2005b). Nemat-Nasser and Isaacs ...
A coupled temperature and strain rate microstructure physically based yield function is proposed ... more A coupled temperature and strain rate microstructure physically based yield function is proposed in this work. It is incorporated along with the Clausius–Duhem inequality and an appropriate free energy definition in a general thermodynamic framework for deriving a three-dimensional kinematical model for thermo-viscoplastic deformations of body centered cubic (bcc) metals. The evolution equations are expressed in terms of the material
... Combination of physically based constitutive models for body centered cubic (bcc) and face ce... more ... Combination of physically based constitutive models for body centered cubic (bcc) and face centered cubic (fcc) metals developed recently by the authors [Voyiadjis, GZ, Abed, FH, 2005. ... In addition, the experimental observations of AL-6XN conducted by Nemat-Nasser et al. ...
Journal of Engineering Materials and Technology-transactions of The Asme, Mar 27, 2012
This study investigates and compares several available plasticity models used to describe the the... more This study investigates and compares several available plasticity models used to describe the thermomechanical behavior of structural steel subjected to complex loadings. The main purpose of this comparison is to select a proper constitutive model that can later be implemented into a finite element code to capture localizations (e.g., shear bands and necking) in steel and steel structures subjected to low- and high-velocity impact. Four well-known constitutive models for viscoplastic deformation of metals, i.e., Johnson–Cook (JC), Zerilli–Armstrong (ZA), Rusinek–Klepaczko (RK), and Voyiadjis–Abed (VA), have been investigated and compared with reference to existing deformation data of HSLA-65 and DH-36 steel conducted at low and high strain rates and various initial temperatures. The JC, ZA, and RK models reasonably describe the flow stress and the strain hardening behavior only in the certain ranges of strain, strain rate, and temperature for which the models were developed. This was attributed to the inaccurate assumptions used in developing these models. In contrast, the VA model most effectively describes the flow stress and strain hardening in which very good predictions are observed for the constitutive behavior of high strength steel over a wide range of strains, strain rates, and temperatures.
Modelling and Simulation in Materials Science and Engineering, Dec 6, 2006
Page 1. Transient localizations in metals using microstructure-based yield surfaces This article ... more Page 1. Transient localizations in metals using microstructure-based yield surfaces This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2007 Modelling Simul. Mater. Sci. Eng. 15 S83 (http://iopscience.iop.org/0965-0393/15/1/S08) ...
Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combi... more Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combinations of temperatures and strain rates. Despite the phenomenon being reported in several other studies, the literature still lacks a specific constitutive model that can physically interpret its effect. Therefore, this work proposes a modification based on physical parameters to the Voyiadjis and Abed (VA) model to account for the effect of DSA in C45 steel. The resulting modified model is then coupled with an energy-based damage model to further capture the effect of material softening. Previously, in VA model, it was assumed that the total activation energy for overcoming the obstacles without external work remains the same which works well in the absence of DSA. However, during DSA, the mobile dislocations are pinned by the diffusing solute atoms. This results in an increase in the total activation free energy needed by the dislocations to overcome the obstacle. Thus, an increase in...
This paper aims at investigating the efficiency of strengthening pre‐damaged circular reinforced ... more This paper aims at investigating the efficiency of strengthening pre‐damaged circular reinforced concrete (RC) columns with Polyparaphenylene Benzobisoxazole fabric‐reinforced cementitious matrix (PBO‐FRCM). The investigated parameters were the degree of pre‐damage (non‐damaged, damaged monotonically up to yielding, or fatigue damaged), the number of PBO‐FRCM layers (0, 2, or 4), and the tie spacing (180 or 90 mm). The experimental results of testing 12 short columns under axial compression showed that PBO‐FRCM systems enhanced the capacity of the non‐damaged columns and successfully restored and further enhanced the capacity of the pre‐damaged columns. Columns strengthened with two and four PBO‐FRCM layers showed a gain in the capacity of up to 40% and 75%, respectively. Furthermore, PBO‐FRCM wrapping enhanced the ductility of both the non‐damaged and the pre‐damaged columns, in which ductility improvement was more noticeable in columns with the larger tie spacing. Finally, the the...
Journal of Engineering Materials and Technology-transactions of The Asme, Aug 4, 2023
Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combi... more Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combinations of temperatures and strain rates. Despite the phenomenon being reported in several other studies, the literature still lacks a specific constitutive model that can physically interpret its effect. Therefore, this work proposes a modification based on physical parameters to the Voyiadjis and Abed (VA) model to account for the effect of DSA in C45 steel. The resulting modified model is then coupled with an energy-based damage model to further capture the effect of material softening. Previously, in VA model, it was assumed that the total activation energy for overcoming the obstacles without external work remains the same which works well in the absence of DSA. However, during DSA, the mobile dislocations are pinned by the diffusing solute atoms. This results in an increase in the total activation free energy needed by the dislocations to overcome the obstacle. Thus, an increase in strength is observed. It is shown in the current work that utilizing the concept of increased solute concentrations at local obstacles, in conjunction with the physical description that the VA model is based upon, successfully captures the phenomenon of DSA in C45 steel. In addition, the metal experiencing softening after reaching its ultimate strength is due to the significant growth of voids and cracks within the microstructure. To capture this behavior, an energy-based damage parameter is incorporated into the proposed model. The coupled plasticity-damage model shows a good comparison with the experimental results.
International Journal for Multiscale Computational Engineering, 2007
ABSTRACT In general, metal structures display a strong rate and temperature dependence when defor... more ABSTRACT In general, metal structures display a strong rate and temperature dependence when deformed nonuniformly into the inelastic range. This effect has important implications for an increasing number of applications in structural and engineering mechanics. The mechanical behavior of these applications cannot be characterized by classical (rate-independent) continuum theories because they incorporate no material length scales. It is therefore necessary to develop a rate-dependent (viscoplasticity) continuum theory bridging the gap between the classical continuum theories and the microstructure simulations. A finite strain hypoelastoviscoplastic framework is developed for body-centered cubic metals using the corotational formulation approach. Material length scales are implicitly introduced into the governing equations through material rate dependency (viscosity). An implicit objective stress update, which is an efficient algorithm for the type of nonlinear problems considered here, is employed. The effectiveness of the present approach is tested by studying strain localizations in a simple tensile plane strain problem and in a cylindrical hat-shaped sample over a wide range of initial temperatures and strain rates. The finite element simulations of material instability problems converge to meaningful results on further refinement of the finite element mesh. Comparisons of the simulation results of adiabatic shear localizations are also made, with experimental results conducted by different authors. Results indicate an excellent performance of the present framework in describing the strain localization problem for niobium, vanadium, and tantalum.
Mechanics of Time-dependent Materials, Mar 11, 2010
... inconsistencies, in fact, are attributed to certain assumptions used in the ZA model formulat... more ... inconsistencies, in fact, are attributed to certain assumptions used in the ZA model formulation that cause the model parameters to be inaccurately re-lated to the microstructural physical quantities (see, for more details, Abed and Voyiadjis 2005b). Nemat-Nasser and Isaacs ...
A coupled temperature and strain rate microstructure physically based yield function is proposed ... more A coupled temperature and strain rate microstructure physically based yield function is proposed in this work. It is incorporated along with the Clausius–Duhem inequality and an appropriate free energy definition in a general thermodynamic framework for deriving a three-dimensional kinematical model for thermo-viscoplastic deformations of body centered cubic (bcc) metals. The evolution equations are expressed in terms of the material
... Combination of physically based constitutive models for body centered cubic (bcc) and face ce... more ... Combination of physically based constitutive models for body centered cubic (bcc) and face centered cubic (fcc) metals developed recently by the authors [Voyiadjis, GZ, Abed, FH, 2005. ... In addition, the experimental observations of AL-6XN conducted by Nemat-Nasser et al. ...
Journal of Engineering Materials and Technology-transactions of The Asme, Mar 27, 2012
This study investigates and compares several available plasticity models used to describe the the... more This study investigates and compares several available plasticity models used to describe the thermomechanical behavior of structural steel subjected to complex loadings. The main purpose of this comparison is to select a proper constitutive model that can later be implemented into a finite element code to capture localizations (e.g., shear bands and necking) in steel and steel structures subjected to low- and high-velocity impact. Four well-known constitutive models for viscoplastic deformation of metals, i.e., Johnson–Cook (JC), Zerilli–Armstrong (ZA), Rusinek–Klepaczko (RK), and Voyiadjis–Abed (VA), have been investigated and compared with reference to existing deformation data of HSLA-65 and DH-36 steel conducted at low and high strain rates and various initial temperatures. The JC, ZA, and RK models reasonably describe the flow stress and the strain hardening behavior only in the certain ranges of strain, strain rate, and temperature for which the models were developed. This was attributed to the inaccurate assumptions used in developing these models. In contrast, the VA model most effectively describes the flow stress and strain hardening in which very good predictions are observed for the constitutive behavior of high strength steel over a wide range of strains, strain rates, and temperatures.
Modelling and Simulation in Materials Science and Engineering, Dec 6, 2006
Page 1. Transient localizations in metals using microstructure-based yield surfaces This article ... more Page 1. Transient localizations in metals using microstructure-based yield surfaces This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2007 Modelling Simul. Mater. Sci. Eng. 15 S83 (http://iopscience.iop.org/0965-0393/15/1/S08) ...
Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combi... more Dynamic strain aging (DSA) is a sudden increase in the strength of a material under certain combinations of temperatures and strain rates. Despite the phenomenon being reported in several other studies, the literature still lacks a specific constitutive model that can physically interpret its effect. Therefore, this work proposes a modification based on physical parameters to the Voyiadjis and Abed (VA) model to account for the effect of DSA in C45 steel. The resulting modified model is then coupled with an energy-based damage model to further capture the effect of material softening. Previously, in VA model, it was assumed that the total activation energy for overcoming the obstacles without external work remains the same which works well in the absence of DSA. However, during DSA, the mobile dislocations are pinned by the diffusing solute atoms. This results in an increase in the total activation free energy needed by the dislocations to overcome the obstacle. Thus, an increase in...
This paper aims at investigating the efficiency of strengthening pre‐damaged circular reinforced ... more This paper aims at investigating the efficiency of strengthening pre‐damaged circular reinforced concrete (RC) columns with Polyparaphenylene Benzobisoxazole fabric‐reinforced cementitious matrix (PBO‐FRCM). The investigated parameters were the degree of pre‐damage (non‐damaged, damaged monotonically up to yielding, or fatigue damaged), the number of PBO‐FRCM layers (0, 2, or 4), and the tie spacing (180 or 90 mm). The experimental results of testing 12 short columns under axial compression showed that PBO‐FRCM systems enhanced the capacity of the non‐damaged columns and successfully restored and further enhanced the capacity of the pre‐damaged columns. Columns strengthened with two and four PBO‐FRCM layers showed a gain in the capacity of up to 40% and 75%, respectively. Furthermore, PBO‐FRCM wrapping enhanced the ductility of both the non‐damaged and the pre‐damaged columns, in which ductility improvement was more noticeable in columns with the larger tie spacing. Finally, the the...
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