Avraham Dorogoy - Academia.edu (original) (raw)
Papers by Avraham Dorogoy
Engineering Fracture Mechanics, 1989
Journal of Sound and Vibration, 2009
ABSTRACT An experimental and numerical study of a non-uniform impact excitation of a circular bar... more ABSTRACT An experimental and numerical study of a non-uniform impact excitation of a circular bar is reported. In experiments, nine strikers with different contact area were accelerated against a circular bar. Axial surface strain of the impacted bar was measured at several distances from the impinged end to include the near and the far fields. The same experimental conditions were solved numerically using a commercial finite element code. It was demonstrated that the far-field response is insensitive to both the size and the form of the striker's colliding end. The distance at which such insensitivity is set is estimated to be approximately one and a half bar diameters.
Experimental Mechanics
This paper introduces a double shear axisymmetric specimen (Shear Compression Disk) and the metho... more This paper introduces a double shear axisymmetric specimen (Shear Compression Disk) and the methodology to extract flow and fracture properties of ductile materials, under various stress triaxiality levels. A thorough numerical investigation of the experimental set-up is performed, which reveals that the stresses are quite uniformly distributed in the gauge section during all the stages of the test. The attainable level of stress triaxiality (with pressures of up to 1.9 GPa) ranges from −0.1 to 1, which can be adjusted by a proper choice of geometrical parameters of the specimen. The methodology is implemented to quasi-static experiments on 4340 Steel and Aluminum 7075-T651 specimens. The flow properties are compared to those obtained by upsetting cylinders and show a very good agreement. For these materials it is observed that, contrary to the fracture strain, the flow properties are quite insensitive to the level of stress triaxiality. The fracture strain of the aluminum alloy increases with triaxiality and may be fitted with an exponential polynomial of the type suggested by [27]. These examples demonstrate the potential of the new specimen to obtain flow and fracture properties of ductile materials under controlled triaxiality.
International Journal of Impact Engineering, 2011
The penetration and perforation of a thick polycarbonate (PC) plate (one and 3 stacked) by an arm... more The penetration and perforation of a thick polycarbonate (PC) plate (one and 3 stacked) by an armor piercing 7.62 mm projectile is investigated experimentally and numerically. The characteristic structure of the projectile's trajectory in the PC plates is studied. It is observed that the trajectory consist of a cavity and a circumferential cracked zone attached to it, which is fully embedded within a cylindrical plastic zone. The size of the plastic zone is approximately twice that of the cavity zone and can be clearly observed due to the change of the refractive properties of the material. Strong local recovery of the PC is shown as well.
Experimental Mechanics, 2009
This note addresses the determination of the Johnson-Cook material parameters using the shear com... more This note addresses the determination of the Johnson-Cook material parameters using the shear compression specimen (SCS). This includes the identification of the thermal softening effect in quasi static and dynamic loading as well as and the strain rate hardening effect in dynamic loading. A hybrid experimental–numerical (finite element) procedure is presented to identify the constitutive parameters, with an application to Ti6Al4V alloy. The present results demonstrate the suitability of the SCS for constitutive testing.
International Journal of Impact Engineering, 2008
This work addresses the effect of small geometrical imperfections on adiabatic shear band (ASB) f... more This work addresses the effect of small geometrical imperfections on adiabatic shear band (ASB) formation. The separate effect of the length and radius of short notches is systematically investigated in AM50 and Ti6Al4V alloys, using shear compression specimens. It is observed that the length of the imperfection does not influence ASB formation in these experiments. By contrast, the notch-root radius appears to be the dominant parameter for the two materials, in perfect agreement with the analytical predictions of . The distribution of deformation energy over the gauge length is modeled numerically. The calculated average dynamic deformation energy levels are quite similar to those that are measured for the two investigated alloys. It is concluded that the global measure of the dynamic deformation energy provides valuable information about ASB failure from geometrical imperfections.
Journal of The Mechanics and Physics of Solids, 2010
The numerical simulation of dynamic structural failure by localized shear is quite complex in ter... more The numerical simulation of dynamic structural failure by localized shear is quite complex in terms of constitutive models and choice of adequate failure criteria, along with a pronounced mesh-sensitivity. As a result, the existing numerical procedures are usually quite sophisticated, so that their application for design purposes is still limited. This study is based on the implementation of a simple energy-based criterion which was developed on experimental considerations , and uses a minimal number of adjustable parameters. According to this criterion, a material point starts to fail when the total strain energy density reaches a critical value. Thereafter, the strength of the element decreases gradually to zero to mimic the actual structural behavior. The criterion was embedded into commercial finite element software, and tested by simulating numerically four typical high-rate experiments. The first is the dynamic torsion test of a tubular specimen. The second concerns the failure mode transition in mode II fracture of an edge crack in plain strain. The last two involve dynamic shear localization under high rate compression of a cylindrical and a shear compression specimen. A very good adequation was found both qualitatively and quantitatively. Qualitatively, in terms of failure path selection, and quantitatively in terms of local strains, temperatures and critical impact velocity. The proposed approach is enticing from an engineering perspective aimed at predicting the onset and propagation of dynamic shear localization in actual structures.
International Journal of Impact Engineering, 2010
The penetration and perforation of a polymethylmethacrylate (PMMA) plate is investigated experime... more The penetration and perforation of a polymethylmethacrylate (PMMA) plate is investigated experimentally and numerically. Two combined failure criteria are used in the numerical analyses: ductile failure with damage evolution and tensile failure. The measured mechanical properties of PMMA are input to the analysis. The determination of the damage evolution parameter in this material is calibrated by simulating and replicating shear localization results obtained in confined PMMA cylinders. The numerical simulation based on these parameters is tested by comparing the numerical trajectory prediction to actual trajectories of inclined impacts of projectiles. The first comparison is qualitative and shows that the numerical simulation predicts ricochet of a projectile impacting at an angle of inclination 30 as reported by [1]. Additional successful comparison with experimental results of inclined impact of a 0.5 00 AP projectile on 3 PMMA plates is reported. The contribution of each failure criterion to the projectile trajectory is studied, showing that the ductile failure criterion enforces a straight trajectory in the initial velocity direction while the tensile failure criterion controls the deflection and ricochet phenomenon. The numerical analyses are further used to study the effect of the angle of inclination on the trajectory and kinetic energy of the projectile. The effect of the projectile mass and impact velocity on the depth of penetration (DOP) was investigated too. It is found that the ricochet phenomenon happens for angles of inclination of 0 < a 30 . The projectile perforates the plate for 50 a 90 , thus defining a failure envelope for this experimental configuration. For normal impact (a ¼ 90 ) the DOP scales linearly with the projectile's mass and can be fitted by a square polynomial with the impact velocity.
Experimental Mechanics, 2005
The shear compression specimen (SCS), which is used for large strain testing, is thoroughly inves... more The shear compression specimen (SCS), which is used for large strain testing, is thoroughly investigated numerically using three-dimensional elastoplastic finite element simulations. In this first part of the study we address quasi-static loading. A bi-linear material model is assumed. We investigate the effect of geometrical parameters, such as gage height and root radius, on the stress and strain distribution and concentration. The analyses show that the stresses and strains are reasonably uniform on a typical gage mid-section, and their average values reflect accurately the prescribed material model. We derive accurate correlations between the averaged von Mises stress and strain and the applied experimental load and displacement. These relations depend on the specimen geometry and the material properties. Numerical results are compared to experimental data, and an excellent agreement is observed. This study confirms the potential of the SCS for large strain testing of material.
International Journal of Impact Engineering, 2008
A combined experimental-numerical analysis was performed to model transverse impact of free-free ... more A combined experimental-numerical analysis was performed to model transverse impact of free-free square aluminum beams loaded at different locations along their length. The applied impact load was obtained from tests carried out on a single Hopkinson pressure bar. The 3D elastic-plastic numerical simulations show that the plastic deformation, adjacent to the impact location, is due to combined dominant bending and stretching modes. Most of the plastic deformation is confined to the impact zone but some partial additional plastic hinges are observed to develop. The plastic strain magnitude and distribution near the impact zone is similar for all tested impact locations, but higher for the more symmetrical impacts. The conversion of impact energy into kinetic, elastic strain energy and plastic dissipation work is characterized for various impact locations along the beam. It is observed that symmetrical impact results in higher plastic dissipation and lower kinetic energy as opposed to unsymmetrical impact. Between 50% and 72% of the applied energy is converted into plastic dissipation energy.
Experimental Mechanics, 2005
The shear compression specimen (SCS), which is used for large strain testing, is thoroughly inves... more The shear compression specimen (SCS), which is used for large strain testing, is thoroughly investigated numerically using three-dimensional elastoplastic finite element simulations. In this first part of the study we address quasi-static loading. A bi-linear material model is assumed. We investigate the effect of geometrical parameters, such as gage height and root radius, on the stress and strain distribution and concentration. The analyses show that the stresses and strains are reasonably uniform on a typical gage mid-section, and their average values reflect accurately the prescribed material model. We derive accurate correlations between the averaged von Mises stress and strain and the applied experimental load and displacement. These relations depend on the specimen geometry and the material properties. Numerical results are compared to experimental data, and an excellent agreement is observed. This study confirms the potential of the SCS for large strain testing of material.
Engineering Fracture Mechanics, 2008
Keywords: 15
Experimental Mechanics, 2005
The shear compression specimen (SCS), which is used for large strain testing, is thoroughly inves... more The shear compression specimen (SCS), which is used for large strain testing, is thoroughly investigated numerically using three-dimensional elastoplastic finite element simulations. In this first part of the study we address quasi-static loading. A bi-linear material model is assumed. We investigate the effect of geometrical parameters, such as gage height and root radius, on the stress and strain distribution and concentration. The analyses show that the stresses and strains are reasonably uniform on a typical gage mid-section, and their average values reflect accurately the prescribed material model. We derive accurate correlations between the averaged von Mises stress and strain and the applied experimental load and displacement. These relations depend on the specimen geometry and the material properties. Numerical results are compared to experimental data, and an excellent agreement is observed. This study confirms the potential of the SCS for large strain testing of material.
Journal of The Mechanics and Physics of Solids, 2008
This paper details a methodology to test the mechanical response of soft, pressure sensitive mate... more This paper details a methodology to test the mechanical response of soft, pressure sensitive materials, over a wide range of strain rates. A hybrid experimental-numerical procedure is used to assess the constitutive parameters. The experimental phase involves axial compression of a cylindrical specimen which is confined by a tightly-fit sleeve that is allowed to yield plastically, thus applying a constant confining pressure. The usually neglected frictional effects between the specimen and the sleeve are fully accounted for and characterized in detail. With commercial polycarbonate as a typical example, it is shown that pressure-sensitivity and rate-sensitivity are not coupled, thus reducing the number of tests needed to characterize a material. The results of numerical simulations indicate that the pressure sensitivity index (angle β in the Drucker-Prager material model) has little influence on the hydrostatic and confining pressures, whereas the equivalent stress sustained by the specimen increases with β, which for commercial polycarbonate is found to be 0 15 β = .
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2004
The quasi-static and dynamic mechanical and failure properties of a swaged tungsten-base heavy al... more The quasi-static and dynamic mechanical and failure properties of a swaged tungsten-base heavy alloy rod have been investigated, with emphasis on the orientation of the specimens in the rod. Three orientations were considered, 0, 45, and 90 deg, with respect to the longitudinal axis of the rod. Compression, tension, and dominant shear tests were carried out. With the exception of the 0 deg orientation, all the orientations displayed quite similar mechanical characteristics in tension and compression. Dynamic shear revealed a critical strain for adiabatic shear failure of ɛ c ≈0.13, independent of the orientation and quite inferior to the quasi-static ductility. The present study confirms previous results obtained for one (generally unspecified) orientation and extends them to three orientations. Failure mechanisms were thoroughly characterized and it appears that significant damage does not develop prior to final failure. It is concluded that, for practical purposes, the swaged heavy alloy considered here can be regarded as isotropic from a mechanical and failure point of view, in spite of its microstructural anisotropy resulting from the swaging process.
Experimental Mechanics, 2006
This paper addresses quasi-static loading of the shear compression specimen (SCS), that has been ... more This paper addresses quasi-static loading of the shear compression specimen (SCS), that has been especially developed to investigate the shear response of materials at various strain rates. Previous work [4, 5] addressed bi-linear hardening materials, whereas the present work concerns parabolic hardening materials. The investigation is done numerically using three-dimensional elastoplastic finite element simulations. The analyses show that the averaged von Mises stress ( \(\widehat{\sigma }_{{eq}} \) ) and strain ( \(\widehat{\varepsilon }_{{{\text{eq}}}} \) ) on a mid-section of the gauge reflect accurately the prescribed parabolic hardening model. A method for finding the parabolic hardening coefficients and reducing the measured load, P, and displacement, d, into equivalent stress \(\widehat{\sigma }_{{eq}} \) and strain \(\widehat{\varepsilon }_{{{\text{eq}}}} \) is introduced and tested. A very good agreement is observed, thus confirming the potential of the technique for large strain testing of parabolic hardening materials.
Engineering Fracture Mechanics, 2005
... Avraham Dorogoy 1 , E-mail The Corresponding Author and Leslie Banks-Sills Corresponding Auth... more ... Avraham Dorogoy 1 , E-mail The Corresponding Author and Leslie Banks-Sills Corresponding Author Contact Information , E-mail The Corresponding Author. ... One of the formulations described by Matos et al. [20] for M is followed, here. ...
International Journal for Numerical Methods in Engineering, 2004
Formulation of the elastic two-dimensional problem of contact with friction is presented. Two-dim... more Formulation of the elastic two-dimensional problem of contact with friction is presented. Two-dimensional equilibrium equations and boundary conditions in an orthogonal curvilinear co-ordinate system are written explicitly. The above formulation is solved with the aid of the finite difference technique. An iterative algorithm which does not require load increments is employed for solving interface fracture problems with contact and friction subjected to a monotonically increasing load. The J-integral is extended for problems in which there is friction along the crack faces. Stress intensity factors are calculated by means of the J-integral, as well as an asymptotic expansion of the tangential shift. Two problems are analysed: (1) a crack in homogeneous material in the presence of friction involving stationary contact; and (2) an interface crack in the presence of friction involving receding contact. Results are compared to those found by analytical and semi-analytical methods which are presented in the literature, as well as to those obtained by means of the finite element method. The accuracy of the results establishes the reliability of the finite difference analysis, as well as the post-processors. In addition, a problem involving stick conditions is considered. It is observed that with increasing friction, the normal gaps and tangential shifts decrease. The size of the contact zone increases and values of the stress intensity factor decrease. Copyright © 2004 John Wiley & Sons, Ltd.
ABSTRACT Formulation of the elastic two-dimensional problem of contact with friction is presented... more ABSTRACT Formulation of the elastic two-dimensional problem of contact with friction is presented. Two-dimensional equilibrium equations and boundary conditions in an orthogonal curvilinear co-ordinate system are written explicitly. The above formulation is solved with the aid of the finite difference technique. An iterative algorithm which does not require load increments is employed for solving interface fracture problems with contact and friction subjected to a monotonically increasing load. The J-integral is extended for problems in which there is friction along the crack faces. Stress intensity factors are calculated by means of the J-integral, as well as an asymptotic expansion of the tangential shift. Two problems are analysed: (1) a crack in homogeneous material in the presence of friction involving stationary contact; and (2) an interface crack in the presence of friction involving receding contact. Results are compared to those found by analytical and semi-analytical methods which are presented in the literature, as well as to those obtained by means of the finite element method. The accuracy of the results establishes the reliability of the finite difference analysis, as well as the post-processors. In addition, a problem involving stick conditions is considered. It is observed that with increasing friction, the normal gaps and tangential shifts decrease. The size of the contact zone increases and values of the stress intensity factor decrease. Copyright © 2004 John Wiley & Sons, Ltd.
Engineering Fracture Mechanics, 1989
Journal of Sound and Vibration, 2009
ABSTRACT An experimental and numerical study of a non-uniform impact excitation of a circular bar... more ABSTRACT An experimental and numerical study of a non-uniform impact excitation of a circular bar is reported. In experiments, nine strikers with different contact area were accelerated against a circular bar. Axial surface strain of the impacted bar was measured at several distances from the impinged end to include the near and the far fields. The same experimental conditions were solved numerically using a commercial finite element code. It was demonstrated that the far-field response is insensitive to both the size and the form of the striker's colliding end. The distance at which such insensitivity is set is estimated to be approximately one and a half bar diameters.
Experimental Mechanics
This paper introduces a double shear axisymmetric specimen (Shear Compression Disk) and the metho... more This paper introduces a double shear axisymmetric specimen (Shear Compression Disk) and the methodology to extract flow and fracture properties of ductile materials, under various stress triaxiality levels. A thorough numerical investigation of the experimental set-up is performed, which reveals that the stresses are quite uniformly distributed in the gauge section during all the stages of the test. The attainable level of stress triaxiality (with pressures of up to 1.9 GPa) ranges from −0.1 to 1, which can be adjusted by a proper choice of geometrical parameters of the specimen. The methodology is implemented to quasi-static experiments on 4340 Steel and Aluminum 7075-T651 specimens. The flow properties are compared to those obtained by upsetting cylinders and show a very good agreement. For these materials it is observed that, contrary to the fracture strain, the flow properties are quite insensitive to the level of stress triaxiality. The fracture strain of the aluminum alloy increases with triaxiality and may be fitted with an exponential polynomial of the type suggested by [27]. These examples demonstrate the potential of the new specimen to obtain flow and fracture properties of ductile materials under controlled triaxiality.
International Journal of Impact Engineering, 2011
The penetration and perforation of a thick polycarbonate (PC) plate (one and 3 stacked) by an arm... more The penetration and perforation of a thick polycarbonate (PC) plate (one and 3 stacked) by an armor piercing 7.62 mm projectile is investigated experimentally and numerically. The characteristic structure of the projectile's trajectory in the PC plates is studied. It is observed that the trajectory consist of a cavity and a circumferential cracked zone attached to it, which is fully embedded within a cylindrical plastic zone. The size of the plastic zone is approximately twice that of the cavity zone and can be clearly observed due to the change of the refractive properties of the material. Strong local recovery of the PC is shown as well.
Experimental Mechanics, 2009
This note addresses the determination of the Johnson-Cook material parameters using the shear com... more This note addresses the determination of the Johnson-Cook material parameters using the shear compression specimen (SCS). This includes the identification of the thermal softening effect in quasi static and dynamic loading as well as and the strain rate hardening effect in dynamic loading. A hybrid experimental–numerical (finite element) procedure is presented to identify the constitutive parameters, with an application to Ti6Al4V alloy. The present results demonstrate the suitability of the SCS for constitutive testing.
International Journal of Impact Engineering, 2008
This work addresses the effect of small geometrical imperfections on adiabatic shear band (ASB) f... more This work addresses the effect of small geometrical imperfections on adiabatic shear band (ASB) formation. The separate effect of the length and radius of short notches is systematically investigated in AM50 and Ti6Al4V alloys, using shear compression specimens. It is observed that the length of the imperfection does not influence ASB formation in these experiments. By contrast, the notch-root radius appears to be the dominant parameter for the two materials, in perfect agreement with the analytical predictions of . The distribution of deformation energy over the gauge length is modeled numerically. The calculated average dynamic deformation energy levels are quite similar to those that are measured for the two investigated alloys. It is concluded that the global measure of the dynamic deformation energy provides valuable information about ASB failure from geometrical imperfections.
Journal of The Mechanics and Physics of Solids, 2010
The numerical simulation of dynamic structural failure by localized shear is quite complex in ter... more The numerical simulation of dynamic structural failure by localized shear is quite complex in terms of constitutive models and choice of adequate failure criteria, along with a pronounced mesh-sensitivity. As a result, the existing numerical procedures are usually quite sophisticated, so that their application for design purposes is still limited. This study is based on the implementation of a simple energy-based criterion which was developed on experimental considerations , and uses a minimal number of adjustable parameters. According to this criterion, a material point starts to fail when the total strain energy density reaches a critical value. Thereafter, the strength of the element decreases gradually to zero to mimic the actual structural behavior. The criterion was embedded into commercial finite element software, and tested by simulating numerically four typical high-rate experiments. The first is the dynamic torsion test of a tubular specimen. The second concerns the failure mode transition in mode II fracture of an edge crack in plain strain. The last two involve dynamic shear localization under high rate compression of a cylindrical and a shear compression specimen. A very good adequation was found both qualitatively and quantitatively. Qualitatively, in terms of failure path selection, and quantitatively in terms of local strains, temperatures and critical impact velocity. The proposed approach is enticing from an engineering perspective aimed at predicting the onset and propagation of dynamic shear localization in actual structures.
International Journal of Impact Engineering, 2010
The penetration and perforation of a polymethylmethacrylate (PMMA) plate is investigated experime... more The penetration and perforation of a polymethylmethacrylate (PMMA) plate is investigated experimentally and numerically. Two combined failure criteria are used in the numerical analyses: ductile failure with damage evolution and tensile failure. The measured mechanical properties of PMMA are input to the analysis. The determination of the damage evolution parameter in this material is calibrated by simulating and replicating shear localization results obtained in confined PMMA cylinders. The numerical simulation based on these parameters is tested by comparing the numerical trajectory prediction to actual trajectories of inclined impacts of projectiles. The first comparison is qualitative and shows that the numerical simulation predicts ricochet of a projectile impacting at an angle of inclination 30 as reported by [1]. Additional successful comparison with experimental results of inclined impact of a 0.5 00 AP projectile on 3 PMMA plates is reported. The contribution of each failure criterion to the projectile trajectory is studied, showing that the ductile failure criterion enforces a straight trajectory in the initial velocity direction while the tensile failure criterion controls the deflection and ricochet phenomenon. The numerical analyses are further used to study the effect of the angle of inclination on the trajectory and kinetic energy of the projectile. The effect of the projectile mass and impact velocity on the depth of penetration (DOP) was investigated too. It is found that the ricochet phenomenon happens for angles of inclination of 0 < a 30 . The projectile perforates the plate for 50 a 90 , thus defining a failure envelope for this experimental configuration. For normal impact (a ¼ 90 ) the DOP scales linearly with the projectile's mass and can be fitted by a square polynomial with the impact velocity.
Experimental Mechanics, 2005
The shear compression specimen (SCS), which is used for large strain testing, is thoroughly inves... more The shear compression specimen (SCS), which is used for large strain testing, is thoroughly investigated numerically using three-dimensional elastoplastic finite element simulations. In this first part of the study we address quasi-static loading. A bi-linear material model is assumed. We investigate the effect of geometrical parameters, such as gage height and root radius, on the stress and strain distribution and concentration. The analyses show that the stresses and strains are reasonably uniform on a typical gage mid-section, and their average values reflect accurately the prescribed material model. We derive accurate correlations between the averaged von Mises stress and strain and the applied experimental load and displacement. These relations depend on the specimen geometry and the material properties. Numerical results are compared to experimental data, and an excellent agreement is observed. This study confirms the potential of the SCS for large strain testing of material.
International Journal of Impact Engineering, 2008
A combined experimental-numerical analysis was performed to model transverse impact of free-free ... more A combined experimental-numerical analysis was performed to model transverse impact of free-free square aluminum beams loaded at different locations along their length. The applied impact load was obtained from tests carried out on a single Hopkinson pressure bar. The 3D elastic-plastic numerical simulations show that the plastic deformation, adjacent to the impact location, is due to combined dominant bending and stretching modes. Most of the plastic deformation is confined to the impact zone but some partial additional plastic hinges are observed to develop. The plastic strain magnitude and distribution near the impact zone is similar for all tested impact locations, but higher for the more symmetrical impacts. The conversion of impact energy into kinetic, elastic strain energy and plastic dissipation work is characterized for various impact locations along the beam. It is observed that symmetrical impact results in higher plastic dissipation and lower kinetic energy as opposed to unsymmetrical impact. Between 50% and 72% of the applied energy is converted into plastic dissipation energy.
Experimental Mechanics, 2005
The shear compression specimen (SCS), which is used for large strain testing, is thoroughly inves... more The shear compression specimen (SCS), which is used for large strain testing, is thoroughly investigated numerically using three-dimensional elastoplastic finite element simulations. In this first part of the study we address quasi-static loading. A bi-linear material model is assumed. We investigate the effect of geometrical parameters, such as gage height and root radius, on the stress and strain distribution and concentration. The analyses show that the stresses and strains are reasonably uniform on a typical gage mid-section, and their average values reflect accurately the prescribed material model. We derive accurate correlations between the averaged von Mises stress and strain and the applied experimental load and displacement. These relations depend on the specimen geometry and the material properties. Numerical results are compared to experimental data, and an excellent agreement is observed. This study confirms the potential of the SCS for large strain testing of material.
Engineering Fracture Mechanics, 2008
Keywords: 15
Experimental Mechanics, 2005
The shear compression specimen (SCS), which is used for large strain testing, is thoroughly inves... more The shear compression specimen (SCS), which is used for large strain testing, is thoroughly investigated numerically using three-dimensional elastoplastic finite element simulations. In this first part of the study we address quasi-static loading. A bi-linear material model is assumed. We investigate the effect of geometrical parameters, such as gage height and root radius, on the stress and strain distribution and concentration. The analyses show that the stresses and strains are reasonably uniform on a typical gage mid-section, and their average values reflect accurately the prescribed material model. We derive accurate correlations between the averaged von Mises stress and strain and the applied experimental load and displacement. These relations depend on the specimen geometry and the material properties. Numerical results are compared to experimental data, and an excellent agreement is observed. This study confirms the potential of the SCS for large strain testing of material.
Journal of The Mechanics and Physics of Solids, 2008
This paper details a methodology to test the mechanical response of soft, pressure sensitive mate... more This paper details a methodology to test the mechanical response of soft, pressure sensitive materials, over a wide range of strain rates. A hybrid experimental-numerical procedure is used to assess the constitutive parameters. The experimental phase involves axial compression of a cylindrical specimen which is confined by a tightly-fit sleeve that is allowed to yield plastically, thus applying a constant confining pressure. The usually neglected frictional effects between the specimen and the sleeve are fully accounted for and characterized in detail. With commercial polycarbonate as a typical example, it is shown that pressure-sensitivity and rate-sensitivity are not coupled, thus reducing the number of tests needed to characterize a material. The results of numerical simulations indicate that the pressure sensitivity index (angle β in the Drucker-Prager material model) has little influence on the hydrostatic and confining pressures, whereas the equivalent stress sustained by the specimen increases with β, which for commercial polycarbonate is found to be 0 15 β = .
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2004
The quasi-static and dynamic mechanical and failure properties of a swaged tungsten-base heavy al... more The quasi-static and dynamic mechanical and failure properties of a swaged tungsten-base heavy alloy rod have been investigated, with emphasis on the orientation of the specimens in the rod. Three orientations were considered, 0, 45, and 90 deg, with respect to the longitudinal axis of the rod. Compression, tension, and dominant shear tests were carried out. With the exception of the 0 deg orientation, all the orientations displayed quite similar mechanical characteristics in tension and compression. Dynamic shear revealed a critical strain for adiabatic shear failure of ɛ c ≈0.13, independent of the orientation and quite inferior to the quasi-static ductility. The present study confirms previous results obtained for one (generally unspecified) orientation and extends them to three orientations. Failure mechanisms were thoroughly characterized and it appears that significant damage does not develop prior to final failure. It is concluded that, for practical purposes, the swaged heavy alloy considered here can be regarded as isotropic from a mechanical and failure point of view, in spite of its microstructural anisotropy resulting from the swaging process.
Experimental Mechanics, 2006
This paper addresses quasi-static loading of the shear compression specimen (SCS), that has been ... more This paper addresses quasi-static loading of the shear compression specimen (SCS), that has been especially developed to investigate the shear response of materials at various strain rates. Previous work [4, 5] addressed bi-linear hardening materials, whereas the present work concerns parabolic hardening materials. The investigation is done numerically using three-dimensional elastoplastic finite element simulations. The analyses show that the averaged von Mises stress ( \(\widehat{\sigma }_{{eq}} \) ) and strain ( \(\widehat{\varepsilon }_{{{\text{eq}}}} \) ) on a mid-section of the gauge reflect accurately the prescribed parabolic hardening model. A method for finding the parabolic hardening coefficients and reducing the measured load, P, and displacement, d, into equivalent stress \(\widehat{\sigma }_{{eq}} \) and strain \(\widehat{\varepsilon }_{{{\text{eq}}}} \) is introduced and tested. A very good agreement is observed, thus confirming the potential of the technique for large strain testing of parabolic hardening materials.
Engineering Fracture Mechanics, 2005
... Avraham Dorogoy 1 , E-mail The Corresponding Author and Leslie Banks-Sills Corresponding Auth... more ... Avraham Dorogoy 1 , E-mail The Corresponding Author and Leslie Banks-Sills Corresponding Author Contact Information , E-mail The Corresponding Author. ... One of the formulations described by Matos et al. [20] for M is followed, here. ...
International Journal for Numerical Methods in Engineering, 2004
Formulation of the elastic two-dimensional problem of contact with friction is presented. Two-dim... more Formulation of the elastic two-dimensional problem of contact with friction is presented. Two-dimensional equilibrium equations and boundary conditions in an orthogonal curvilinear co-ordinate system are written explicitly. The above formulation is solved with the aid of the finite difference technique. An iterative algorithm which does not require load increments is employed for solving interface fracture problems with contact and friction subjected to a monotonically increasing load. The J-integral is extended for problems in which there is friction along the crack faces. Stress intensity factors are calculated by means of the J-integral, as well as an asymptotic expansion of the tangential shift. Two problems are analysed: (1) a crack in homogeneous material in the presence of friction involving stationary contact; and (2) an interface crack in the presence of friction involving receding contact. Results are compared to those found by analytical and semi-analytical methods which are presented in the literature, as well as to those obtained by means of the finite element method. The accuracy of the results establishes the reliability of the finite difference analysis, as well as the post-processors. In addition, a problem involving stick conditions is considered. It is observed that with increasing friction, the normal gaps and tangential shifts decrease. The size of the contact zone increases and values of the stress intensity factor decrease. Copyright © 2004 John Wiley & Sons, Ltd.
ABSTRACT Formulation of the elastic two-dimensional problem of contact with friction is presented... more ABSTRACT Formulation of the elastic two-dimensional problem of contact with friction is presented. Two-dimensional equilibrium equations and boundary conditions in an orthogonal curvilinear co-ordinate system are written explicitly. The above formulation is solved with the aid of the finite difference technique. An iterative algorithm which does not require load increments is employed for solving interface fracture problems with contact and friction subjected to a monotonically increasing load. The J-integral is extended for problems in which there is friction along the crack faces. Stress intensity factors are calculated by means of the J-integral, as well as an asymptotic expansion of the tangential shift. Two problems are analysed: (1) a crack in homogeneous material in the presence of friction involving stationary contact; and (2) an interface crack in the presence of friction involving receding contact. Results are compared to those found by analytical and semi-analytical methods which are presented in the literature, as well as to those obtained by means of the finite element method. The accuracy of the results establishes the reliability of the finite difference analysis, as well as the post-processors. In addition, a problem involving stick conditions is considered. It is observed that with increasing friction, the normal gaps and tangential shifts decrease. The size of the contact zone increases and values of the stress intensity factor decrease. Copyright © 2004 John Wiley & Sons, Ltd.