ABSTRACT Numerous experimental investigations clearly established that when soda–lime glass is su... more ABSTRACT Numerous experimental investigations clearly established that when soda–lime glass is subjected to sufficiently high axial-stress/pressure, it displays a nonlinear mechanical response and deformation irreversibility (inelasticity). This portion of the material behavior is often neglected in material models for glass which tend to focus on the damage and fracture phenomena of the material. However, material nonlinearity/inelasticity can, in principle, have a profound effect on wave/shock propagation phenomena and processes (e.g. spall fracture).Within the present work, the effect of material nonlinearity and inelastic behavior on the dynamic response (including spallation) of soda–lime glass is studied under symmetric flyer-plate loading conditions using computational methods and tools. Material nonlinearity and deformation irreversibility are modeled in two different ways: (a) as a non-linear elastic material response with no deformation irreversibility; and (b) as a linear-elastic, volumetrically-plastic deformation response. Incorporation of nonlinearity and inelasticity phenomena into a continuum-level material model for soda–lime glass recently developed by the authors revealed that while these phenomena do not measurably affect spall resistance (as measured by a minimum flyer-plate velocity resulting in spallation), they provide beneficial linear-momentum/kinetic energy reduction effects.
A number of experimental investigations reported in the open literature have indicated that the a... more A number of experimental investigations reported in the open literature have indicated that the application of polyurea coatings can substantially improve blast and ballistic impact resistance/survivability of buildings, vehicles and laboratory test plates. While several potential mechanisms (e.g., shock-impedance mismatch, shock-wave dispersion, fracture-mode conversion and strain delocalization) have been proposed for the observed enhancement in the blast-wave/projectile-energy absorption, direct experimental or analytical evidence for the operation of these mechanisms has been lacking. Recently, it has been proposed that transition of polyurea between its rubbery-state and its glassy-state under high deformation-rate loading conditions is another possible mechanism for the improved ballistic impact resistance of polyurea-coated structures/test plates. In the present work, an attempt is made to provide computational support for this deformation-induced glass transition based energy-dissipation/absorption mechanism. Towards that end, a series of finite-element analyses of the projectile/coated-plate interactions are carried out using a transient non-linear dynamics finite-element approach. The results obtained are used to assess the extent of energy absorption and to identify the mode of failure of the test plate as a function of the imposed impact conditions. The results obtained show that the mechanical response of polyurea under impact conditions is a fairly sensitive function of the difference between the test temperature and the glass transition temperature. Specifically, when this difference is large, polyurea tends to display high-ductility behavior of a stereotypical elastomer in its rubbery-state. On the other hand, when the test temperature is closer to the glass transition temperature, polyurea tends to transform into its glassy-state during deformation and this process is associated with viscous type energy-dissipation. It is also argued that additional energy absorbing/dissipating mechanisms may contribute to the superior ballistic/blast protection capability of polyurea.
Journal of Materials Engineering and Performance, 2010
A set of large-strain/high-deformation-rate/high-pressure material models for sand-based soils wi... more A set of large-strain/high-deformation-rate/high-pressure material models for sand-based soils with different saturation levels and clay and gravel contents was recently proposed and validated in our study, and the same has been extended in this study to include clay-based soils of different saturation levels and sand contents. The model includes an equation of state which reveals the material response under hydrostatic
Journal of Materials Engineering and Performance, 2012
ABSTRACT A fully coupled thermomechanical finite-element analysis of the linear friction welding ... more ABSTRACT A fully coupled thermomechanical finite-element analysis of the linear friction welding (LFW) process is combined with the basic physical metallurgy of Ti-6Al-4V to predict microstructure and mechanical properties within the LFW joints (as a function of the LFW process parameters). A close examination of the experimental results reported in the open literature revealed that the weld region consists of a thermomechanically affected zone (TMAZ) and a heat-affected zone (HAZ) and that the material mechanical properties are somewhat more inferior in the HAZ. Taking this observation into account, a model for microstructure-evolution during LFW was developed and parameterized for the Ti-6Al-4V material residing in the HAZ. Specifically, this model addresses the problem of temporal evolution of the prior β-phase grain size (the dominant microstructural parameter in the HAZ) during the LFW process. This model is next combined with the well-established property versus microstructure correlations in Ti-6Al-4V to predict the overall structural performance of the LFW joint. The results obtained are found to be in reasonably good agreement with their experimental counterparts suggesting that the present computational approach may be used to guide the selection of the LFW process parameters to optimize the structural performance of the LFW joints.
Journal of Materials Engineering and Performance, 2013
ABSTRACT Fiber-reinforced polymer matrix composite materials display quite complex deformation an... more ABSTRACT Fiber-reinforced polymer matrix composite materials display quite complex deformation and failure behavior under ballistic/blast impact loading conditions. This complexity is generally attributed to a number of factors such as (a) hierarchical/multi-length scale architecture of the material microstructure; (b) nonlinear, rate-dependent and often pressure-sensitive mechanical response; and (c) the interplay of various intrinsic phenomena and processes such as fiber twisting, interfiber friction/sliding, etc. Material models currently employed in the computational engineering analyses of ballistic/blast impact protective structures made of this type of material do not generally include many of the aforementioned aspects of the material dynamic behavior. Consequently, discrepancies are often observed between computational predictions and their experimental counterparts. To address this problem, the results of an extensive set of molecular-level computational analyses regarding the role of various microstructural/morphological defects on the Kevlar® fiber mechanical properties are used to upgrade one of the existing continuum-level material models for fiber-reinforced composites. The results obtained show that the response of the material is significantly affected as a result of the incorporation of microstructural effects both under quasi-static simple mechanical testing condition and under dynamic ballistic-impact conditions.
Journal of Materials Engineering and Performance, 2011
Two representative soil models are compared and contrasted within two transient nonlinear dynamic... more Two representative soil models are compared and contrasted within two transient nonlinear dynamics computational analyses. The first soil model is representative of a discrete-particle group of models, while the other is a typical continuum-type consolidated-soil model. The two computational analyses involved: (a) the case of a soil slug impacting a rigid flat surface and (b) the case of detonation of
Various open-literature experimental findings pertaining to the ballistic behavior of glass are u... more Various open-literature experimental findings pertaining to the ballistic behavior of glass are used to construct a simple, physically based, high strain-rate, high-pressure, large-strain constitutive model for this material. The basic components of the model are constructed in such a way that the model is suitable for direct incorporation into standard commercial transient non-linear dynamics finite-element based software packages like ANSYS/Autodyn
Traumatic brain injury (TBI) is generally considered as a signature injury of the current militar... more Traumatic brain injury (TBI) is generally considered as a signature injury of the current military conflicts, with costly and life-altering long-term effects. Hence, there is an urgent need to combat this problem by both gaining a better understanding of the mechanisms responsible for the blast-induced TBI and by designing/developing more effective head protection systems. In the present work, the blast-wave impact-mitigation ability of polyurea when used as a helmet suspension-pad material is investigated computationally. Towards that end, a combined Eulerian/Lagrangian fluid/solid transient non-linear dynamics computational analysis is carried out at two levels of blast peak overpressure: (a) one level corresponding to the unprotected-lung-injury-threshold; and (b) the other level associated with the corresponding 50% lethal dose (LD 50), i.e. with a 50% probability for lung-injury induced death. To assess the blast-wave impact-mitigation ability of polyurea, the temporal evolution of the axial stress and the particle (axial) velocity at different locations within the intra-cranial cavity are analyzed. The results are compared with their counterparts obtained in the case of a conventional foam suspension-pad material. This comparison showed that, the use of polyurea suspension pads is associated with a substantially greater reduction in the peak loading experienced by the brain relative to that observed in the case of the conventional foam. The observed differences in the blast-wave mitigation capability of the conventional foam and polyurea are next rationalized in terms of the differences in their microstructure and in their mechanical response when subjected to blast loading.
Multidiscipline Modeling in Materials and Structures, 2009
A large-strain/high-deformation rate model for clay-free sand recently proposed and validated in ... more A large-strain/high-deformation rate model for clay-free sand recently proposed and validated in our work [1,2], has been extended to sand containing relatively small (< 15vol.%) of clay and having various levels of saturation with water. The model includes an equation of state which represents the material response under hydrostatic pressure, a strength model which captures material behavior under elastic-plastic conditions
Multidiscipline Modeling in Materials and Structures, 2011
Purpose – The purpose of this paper is to develop and parameterize a time-invariant (equilibrium)... more Purpose – The purpose of this paper is to develop and parameterize a time-invariant (equilibrium) material mechanical model for segmented polyureas, a class of thermoplastically linked co-polymeric elastomers, using experimental data available in open literature. Design/methodology/approach – The key components of the model are developed by first constructing a simple molecular-level microstructure model and by relating the microstructural elements and
Multidiscipline Modeling in Materials and Structures, 2011
Purpose – The purpose of this paper is to compare fracture-fixation and bone-healing promotion ef... more Purpose – The purpose of this paper is to compare fracture-fixation and bone-healing promotion efficacies of an intramedullary (IM) nail-type and an external osteosynthesis plate-type femoral trochanteric-fracture implants using the results of a combined multi-body dynamics and finite element analyses. For both implants, fracture fixation was obtained using a dynamic hip blade which is anchored to the femur head on
Multidiscipline Modeling in Materials and Structures, 2007
... pressure versus time signals and visual observation clearly show the differences in the blast... more ... pressure versus time signals and visual observation clearly show the differences in the blast loads resulting from the landmine detonation in ... It is well established that light-armored and soft-skinned vehicles are highly vulnerable to anti-vehicular mine blasts [eg1]. Traditionally ...
Multidiscipline Modeling in Materials and Structures, 2011
Purpose – Propagation of planar (i.e. one directional), longitudinal (i.e. uniaxial strain), stea... more Purpose – Propagation of planar (i.e. one directional), longitudinal (i.e. uniaxial strain), steady (i.e. time-invariant) structured shock waves within metal matrix composites (MMCs) is studied computationally. Waves of this type are typically generated during blast-wave loading or ballistic impact and play a major role in the way blast/ballistic impact loads are introduced in, and applied to, a target structure. Hence,
ABSTRACT Numerous experimental investigations clearly established that when soda–lime glass is su... more ABSTRACT Numerous experimental investigations clearly established that when soda–lime glass is subjected to sufficiently high axial-stress/pressure, it displays a nonlinear mechanical response and deformation irreversibility (inelasticity). This portion of the material behavior is often neglected in material models for glass which tend to focus on the damage and fracture phenomena of the material. However, material nonlinearity/inelasticity can, in principle, have a profound effect on wave/shock propagation phenomena and processes (e.g. spall fracture).Within the present work, the effect of material nonlinearity and inelastic behavior on the dynamic response (including spallation) of soda–lime glass is studied under symmetric flyer-plate loading conditions using computational methods and tools. Material nonlinearity and deformation irreversibility are modeled in two different ways: (a) as a non-linear elastic material response with no deformation irreversibility; and (b) as a linear-elastic, volumetrically-plastic deformation response. Incorporation of nonlinearity and inelasticity phenomena into a continuum-level material model for soda–lime glass recently developed by the authors revealed that while these phenomena do not measurably affect spall resistance (as measured by a minimum flyer-plate velocity resulting in spallation), they provide beneficial linear-momentum/kinetic energy reduction effects.
A number of experimental investigations reported in the open literature have indicated that the a... more A number of experimental investigations reported in the open literature have indicated that the application of polyurea coatings can substantially improve blast and ballistic impact resistance/survivability of buildings, vehicles and laboratory test plates. While several potential mechanisms (e.g., shock-impedance mismatch, shock-wave dispersion, fracture-mode conversion and strain delocalization) have been proposed for the observed enhancement in the blast-wave/projectile-energy absorption, direct experimental or analytical evidence for the operation of these mechanisms has been lacking. Recently, it has been proposed that transition of polyurea between its rubbery-state and its glassy-state under high deformation-rate loading conditions is another possible mechanism for the improved ballistic impact resistance of polyurea-coated structures/test plates. In the present work, an attempt is made to provide computational support for this deformation-induced glass transition based energy-dissipation/absorption mechanism. Towards that end, a series of finite-element analyses of the projectile/coated-plate interactions are carried out using a transient non-linear dynamics finite-element approach. The results obtained are used to assess the extent of energy absorption and to identify the mode of failure of the test plate as a function of the imposed impact conditions. The results obtained show that the mechanical response of polyurea under impact conditions is a fairly sensitive function of the difference between the test temperature and the glass transition temperature. Specifically, when this difference is large, polyurea tends to display high-ductility behavior of a stereotypical elastomer in its rubbery-state. On the other hand, when the test temperature is closer to the glass transition temperature, polyurea tends to transform into its glassy-state during deformation and this process is associated with viscous type energy-dissipation. It is also argued that additional energy absorbing/dissipating mechanisms may contribute to the superior ballistic/blast protection capability of polyurea.
Journal of Materials Engineering and Performance, 2010
A set of large-strain/high-deformation-rate/high-pressure material models for sand-based soils wi... more A set of large-strain/high-deformation-rate/high-pressure material models for sand-based soils with different saturation levels and clay and gravel contents was recently proposed and validated in our study, and the same has been extended in this study to include clay-based soils of different saturation levels and sand contents. The model includes an equation of state which reveals the material response under hydrostatic
Journal of Materials Engineering and Performance, 2012
ABSTRACT A fully coupled thermomechanical finite-element analysis of the linear friction welding ... more ABSTRACT A fully coupled thermomechanical finite-element analysis of the linear friction welding (LFW) process is combined with the basic physical metallurgy of Ti-6Al-4V to predict microstructure and mechanical properties within the LFW joints (as a function of the LFW process parameters). A close examination of the experimental results reported in the open literature revealed that the weld region consists of a thermomechanically affected zone (TMAZ) and a heat-affected zone (HAZ) and that the material mechanical properties are somewhat more inferior in the HAZ. Taking this observation into account, a model for microstructure-evolution during LFW was developed and parameterized for the Ti-6Al-4V material residing in the HAZ. Specifically, this model addresses the problem of temporal evolution of the prior β-phase grain size (the dominant microstructural parameter in the HAZ) during the LFW process. This model is next combined with the well-established property versus microstructure correlations in Ti-6Al-4V to predict the overall structural performance of the LFW joint. The results obtained are found to be in reasonably good agreement with their experimental counterparts suggesting that the present computational approach may be used to guide the selection of the LFW process parameters to optimize the structural performance of the LFW joints.
Journal of Materials Engineering and Performance, 2013
ABSTRACT Fiber-reinforced polymer matrix composite materials display quite complex deformation an... more ABSTRACT Fiber-reinforced polymer matrix composite materials display quite complex deformation and failure behavior under ballistic/blast impact loading conditions. This complexity is generally attributed to a number of factors such as (a) hierarchical/multi-length scale architecture of the material microstructure; (b) nonlinear, rate-dependent and often pressure-sensitive mechanical response; and (c) the interplay of various intrinsic phenomena and processes such as fiber twisting, interfiber friction/sliding, etc. Material models currently employed in the computational engineering analyses of ballistic/blast impact protective structures made of this type of material do not generally include many of the aforementioned aspects of the material dynamic behavior. Consequently, discrepancies are often observed between computational predictions and their experimental counterparts. To address this problem, the results of an extensive set of molecular-level computational analyses regarding the role of various microstructural/morphological defects on the Kevlar® fiber mechanical properties are used to upgrade one of the existing continuum-level material models for fiber-reinforced composites. The results obtained show that the response of the material is significantly affected as a result of the incorporation of microstructural effects both under quasi-static simple mechanical testing condition and under dynamic ballistic-impact conditions.
Journal of Materials Engineering and Performance, 2011
Two representative soil models are compared and contrasted within two transient nonlinear dynamic... more Two representative soil models are compared and contrasted within two transient nonlinear dynamics computational analyses. The first soil model is representative of a discrete-particle group of models, while the other is a typical continuum-type consolidated-soil model. The two computational analyses involved: (a) the case of a soil slug impacting a rigid flat surface and (b) the case of detonation of
Various open-literature experimental findings pertaining to the ballistic behavior of glass are u... more Various open-literature experimental findings pertaining to the ballistic behavior of glass are used to construct a simple, physically based, high strain-rate, high-pressure, large-strain constitutive model for this material. The basic components of the model are constructed in such a way that the model is suitable for direct incorporation into standard commercial transient non-linear dynamics finite-element based software packages like ANSYS/Autodyn
Traumatic brain injury (TBI) is generally considered as a signature injury of the current militar... more Traumatic brain injury (TBI) is generally considered as a signature injury of the current military conflicts, with costly and life-altering long-term effects. Hence, there is an urgent need to combat this problem by both gaining a better understanding of the mechanisms responsible for the blast-induced TBI and by designing/developing more effective head protection systems. In the present work, the blast-wave impact-mitigation ability of polyurea when used as a helmet suspension-pad material is investigated computationally. Towards that end, a combined Eulerian/Lagrangian fluid/solid transient non-linear dynamics computational analysis is carried out at two levels of blast peak overpressure: (a) one level corresponding to the unprotected-lung-injury-threshold; and (b) the other level associated with the corresponding 50% lethal dose (LD 50), i.e. with a 50% probability for lung-injury induced death. To assess the blast-wave impact-mitigation ability of polyurea, the temporal evolution of the axial stress and the particle (axial) velocity at different locations within the intra-cranial cavity are analyzed. The results are compared with their counterparts obtained in the case of a conventional foam suspension-pad material. This comparison showed that, the use of polyurea suspension pads is associated with a substantially greater reduction in the peak loading experienced by the brain relative to that observed in the case of the conventional foam. The observed differences in the blast-wave mitigation capability of the conventional foam and polyurea are next rationalized in terms of the differences in their microstructure and in their mechanical response when subjected to blast loading.
Multidiscipline Modeling in Materials and Structures, 2009
A large-strain/high-deformation rate model for clay-free sand recently proposed and validated in ... more A large-strain/high-deformation rate model for clay-free sand recently proposed and validated in our work [1,2], has been extended to sand containing relatively small (< 15vol.%) of clay and having various levels of saturation with water. The model includes an equation of state which represents the material response under hydrostatic pressure, a strength model which captures material behavior under elastic-plastic conditions
Multidiscipline Modeling in Materials and Structures, 2011
Purpose – The purpose of this paper is to develop and parameterize a time-invariant (equilibrium)... more Purpose – The purpose of this paper is to develop and parameterize a time-invariant (equilibrium) material mechanical model for segmented polyureas, a class of thermoplastically linked co-polymeric elastomers, using experimental data available in open literature. Design/methodology/approach – The key components of the model are developed by first constructing a simple molecular-level microstructure model and by relating the microstructural elements and
Multidiscipline Modeling in Materials and Structures, 2011
Purpose – The purpose of this paper is to compare fracture-fixation and bone-healing promotion ef... more Purpose – The purpose of this paper is to compare fracture-fixation and bone-healing promotion efficacies of an intramedullary (IM) nail-type and an external osteosynthesis plate-type femoral trochanteric-fracture implants using the results of a combined multi-body dynamics and finite element analyses. For both implants, fracture fixation was obtained using a dynamic hip blade which is anchored to the femur head on
Multidiscipline Modeling in Materials and Structures, 2007
... pressure versus time signals and visual observation clearly show the differences in the blast... more ... pressure versus time signals and visual observation clearly show the differences in the blast loads resulting from the landmine detonation in ... It is well established that light-armored and soft-skinned vehicles are highly vulnerable to anti-vehicular mine blasts [eg1]. Traditionally ...
Multidiscipline Modeling in Materials and Structures, 2011
Purpose – Propagation of planar (i.e. one directional), longitudinal (i.e. uniaxial strain), stea... more Purpose – Propagation of planar (i.e. one directional), longitudinal (i.e. uniaxial strain), steady (i.e. time-invariant) structured shock waves within metal matrix composites (MMCs) is studied computationally. Waves of this type are typically generated during blast-wave loading or ballistic impact and play a major role in the way blast/ballistic impact loads are introduced in, and applied to, a target structure. Hence,
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Papers by B. Pandurangan