The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
B A Cheeseman - One of the best experts on this subject based on the ideXlab platform.
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Modifications in the AA5083 Johnson-Cook Material Model for Use in Friction Stir Welding Computational Analyses
Journal of Materials Engineering and Performance, 2012Co-Authors: M Grujicic, B Pandurangan, C.-f. Yen, B A CheesemanAbstract:Johnson-Cook strength Material Model is frequently used in finite-element analyses of various manufacturing processes involving plastic deformation of metallic Materials. The main attraction to this Model arises from its mathematical simplicity and its ability to capture the first-order metal-working effects (e.g., those associated with the influence of plastic deformation, rate of deformation, and the attendant temperature). However, this Model displays serious shortcomings when used in the engineering analyses of various hot-working processes (i.e., those utilizing temperatures higher than the Material recrystallization temperature). These shortcomings are related to the fact that microstructural changes involving: (i) irreversible decrease in the dislocation density due to the operation of annealing/recrystallization processes; (ii) increase in grain-size due to high-temperature exposure; and (iii) dynamic-recrystallization-induced grain refinement are not accounted for by the Model. In this study, an attempt is made to combine the basic physical-metallurgy principles with the associated kinetics relations to properly modify the Johnson-Cook Material Model, so that the Model can be used in the analyses of metal hot-working and joining processes. The Model is next used to help establish relationships between process parameters, Material microstructure and properties in friction stir welding welds of AA5083 (a non-age-hardenable, solid-solution strengthened, strain-hardened/stabilized Al-Mg-Mn alloy).
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development of a meso scale Material Model for ballistic fabric and its use in flexible armor protection systems
Journal of Materials Engineering and Performance, 2010Co-Authors: M Grujicic, G Arakere, T He, W C Bell, B A CheesemanAbstract:A meso-scale ballistic Material Model for a prototypical plain-woven single-ply flexible armor is developed and implemented in a Material user subroutine for the use in commercial explicit finite element programs. The main intent of the Model is to attain computational efficiency when calculating the mechanical response of the multi-ply fabric-based flexible-armor Material during its impact with various projectiles without significantly sacrificing the key physical aspects of the fabric microstructure, architecture, and behavior. To validate the new Model, a comparative finite element method analysis is carried out in which: (a) the plain-woven single-ply fabric is Modeled using conventional shell elements and weaving is done in an explicit manner by snaking the yarns through the fabric and (b) the fabric is treated as a planar continuum surface composed of conventional shell elements to which the new meso-scale unit-cell based Material Model is assigned. The results obtained show that the Material Model provides a reasonably good description for the fabric deformation and fracture behavior under different combinations of fixed and free boundary conditions. Finally, the Model is used in an investigation of the ability of a multi-ply soft-body armor vest to protect the wearer from impact by a 9-mm round nose projectile. The effects of inter-ply friction, projectile/yarn friction, and the far-field boundary conditions are revealed and the results explained using simple wave mechanics principles, high-deformation rate Material behavior, and the role of various energy-absorbing mechanisms in the fabric-based armor systems.
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a meso scale unit cell based Material Model for the single ply flexible fabric armor
Materials & Design, 2009Co-Authors: M Grujicic, G Arakere, T He, W C Bell, B A CheesemanAbstract:A meso-scale unit-cell based Material Model for a prototypical plain-woven single-ply flexible armor is developed and implemented in a Material user subroutine for use in commercial explicit finite element programs. The main intent of the Model is to attain computational efficiency when calculating the mechanical response of the multi-ply fabric-based flexible armor Material during its impact with various projectiles without significantly sacrificing the key physical aspects of the fabric microstructure, architecture and behavior. To validate the new Model, a comparative finite element method (FEM) analysis is carried out in which: (a) the plain-woven single-ply fabric is Modeled using conventional shell elements and weaving is done in an explicit manner by snaking the yarns through the fabric and (b) the fabric is treated as a planar continuum surface composed of conventional shell elements to which the new meso-scale unit-cell based Material Model is assigned. The results obtained show that the Material Model provides a reasonably good description for the fabric deformation and fracture behavior under different combinations of fixed and free boundary conditions.
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computer simulations based development of a high strain rate large deformation high pressure Material Model for stanag 4569 sandy gravel
Soil Dynamics and Earthquake Engineering, 2008Co-Authors: M Grujicic, B A Cheeseman, B Pandurangan, Nicole Coutris, W N Roy, R R SkaggsAbstract:Abstract The NATO Standard Agreement [STANAG 4569, Protection for occupants of logistics and light-armored vehicles] defines the make-up and the conditions of sandy-gravel soil which is used for testing the ability of various armor systems to provide the necessary level of protection. In this paper, an effort is made to develop a high strain-rate, large-strain, high-pressure Material Model for sandy gravel which can be used in transient non-linear dynamic simulations of the interactions between landmine detonation gaseous products, landmine-casing fragments and soil ejecta and the target military vehicles. The Material Model for sandy gravel has been developed by extending the CU–ARL sand Model [Grujicic M, Pandurangan B, Cheeseman BA, Roy WN, Skaggs RR, Gupta R. Parameterization of the porous-Material Model for sand with various degrees of water saturation. Soil Dyn Earthquake Eng 2008;28(1):20–35] in order to include the effects of gravel particles on the equation of state, strength, failure and erosion behavior. Parameterization of the sandy gravel soil Model has been done by carrying out a series of computational experiments pertaining to the deformation and fracture behavior of the two-phase (sand plus gravel) Material. Experimental tests which should be carried out in order to validate the proposed Model have been identified and described.
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application of the modified compaction Material Model to the analysis of landmine detonation in soil with various degrees of water saturation
Shock and Vibration, 2008Co-Authors: M Grujicic, B A Cheeseman, B Pandurangan, W N Roy, J D Summers, R R SkaggsAbstract:A series of transient non-linear dynamics computational analyses of the explosion phenomena accompanying the detonation of a 100 g C4 mine buried in sand to different depths is carried out using the software package AUTODYN. The mechanical response of sand under high deformation-rate conditions has been represented using the modified compaction Material Model developed in our recent work (1). While the mechanical response of the other attendant Materials (air, gaseous-detonation products and AISI 1006 mild steel) is accounted for using the Material Models available in literature. The results obtained (specifically, the temporal evolution of the sand overburden shape and pressure at various locations in air above the detonation site) were compared with their experimental counterparts for a (50wt%-sand/50wt.%-clay) soil obtained recently by Foedinger (2). The comparison revealed that the modified compaction Material Model for sand can account reasonably well for the magnitude, spatial distribution and the temporal evolution of the dynamic loads accompanying detonation of shallow-buried mines in soils with various clay and water contents.
M Grujicic - One of the best experts on this subject based on the ideXlab platform.
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multi length scale Material Model for sic sic ceramic matrix composites cmcs inclusion of in service environmental effects
Journal of Materials Engineering and Performance, 2016Co-Authors: M Grujicic, R Galgalikar, J S Snipes, S RamaswamiAbstract:In our recent work, a multi-length-scale room-temperature Material Model for SiC/SiC ceramic-matrix composites (CMCs) was derived and parameterized. The Model was subsequently linked with a finite-element solver so that it could be used in a general room-temperature, structural/damage analysis of gas-turbine engine CMC components. Due to its multi-length-scale character, the Material Model enabled inclusion of the effects of fiber/tow (e.g., the volume fraction, size, and properties of the fibers; fiber-coating Material/thickness; decohesion properties of the coating/matrix interfaces; etc.) and ply/lamina (e.g., the 0°/90° cross-ply versus plain-weave architectures, the extent of tow crimping in the case of the plain-weave plies, cohesive properties of the inter-ply boundaries, etc.) length-scale microstructural/architectural parameters on the mechanical response of the CMCs. One of the major limitations of the Model is that it applies to the CMCs in their as-fabricated conditions (i.e., the effect of prolonged in-service environmental exposure and the associated Material aging-degradation is not accounted for). In the present work, the Model is upgraded to include such in-service environmental-exposure effects. To demonstrate the utility of the upgraded Material Model, it is used within a finite-element structural/failure analysis involving impact of a toboggan-shaped turbine shroud segment by a foreign object. The results obtained clearly revealed the effects that different aspects of the in-service environmental exposure have on the Material degradation and the extent of damage suffered by the impacted CMC toboggan-shaped shroud segment.
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Modifications in the AA5083 Johnson-Cook Material Model for Use in Friction Stir Welding Computational Analyses
Journal of Materials Engineering and Performance, 2012Co-Authors: M Grujicic, B Pandurangan, C.-f. Yen, B A CheesemanAbstract:Johnson-Cook strength Material Model is frequently used in finite-element analyses of various manufacturing processes involving plastic deformation of metallic Materials. The main attraction to this Model arises from its mathematical simplicity and its ability to capture the first-order metal-working effects (e.g., those associated with the influence of plastic deformation, rate of deformation, and the attendant temperature). However, this Model displays serious shortcomings when used in the engineering analyses of various hot-working processes (i.e., those utilizing temperatures higher than the Material recrystallization temperature). These shortcomings are related to the fact that microstructural changes involving: (i) irreversible decrease in the dislocation density due to the operation of annealing/recrystallization processes; (ii) increase in grain-size due to high-temperature exposure; and (iii) dynamic-recrystallization-induced grain refinement are not accounted for by the Model. In this study, an attempt is made to combine the basic physical-metallurgy principles with the associated kinetics relations to properly modify the Johnson-Cook Material Model, so that the Model can be used in the analyses of metal hot-working and joining processes. The Model is next used to help establish relationships between process parameters, Material microstructure and properties in friction stir welding welds of AA5083 (a non-age-hardenable, solid-solution strengthened, strain-hardened/stabilized Al-Mg-Mn alloy).
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development of a meso scale Material Model for ballistic fabric and its use in flexible armor protection systems
Journal of Materials Engineering and Performance, 2010Co-Authors: M Grujicic, G Arakere, T He, W C Bell, B A CheesemanAbstract:A meso-scale ballistic Material Model for a prototypical plain-woven single-ply flexible armor is developed and implemented in a Material user subroutine for the use in commercial explicit finite element programs. The main intent of the Model is to attain computational efficiency when calculating the mechanical response of the multi-ply fabric-based flexible-armor Material during its impact with various projectiles without significantly sacrificing the key physical aspects of the fabric microstructure, architecture, and behavior. To validate the new Model, a comparative finite element method analysis is carried out in which: (a) the plain-woven single-ply fabric is Modeled using conventional shell elements and weaving is done in an explicit manner by snaking the yarns through the fabric and (b) the fabric is treated as a planar continuum surface composed of conventional shell elements to which the new meso-scale unit-cell based Material Model is assigned. The results obtained show that the Material Model provides a reasonably good description for the fabric deformation and fracture behavior under different combinations of fixed and free boundary conditions. Finally, the Model is used in an investigation of the ability of a multi-ply soft-body armor vest to protect the wearer from impact by a 9-mm round nose projectile. The effects of inter-ply friction, projectile/yarn friction, and the far-field boundary conditions are revealed and the results explained using simple wave mechanics principles, high-deformation rate Material behavior, and the role of various energy-absorbing mechanisms in the fabric-based armor systems.
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a meso scale unit cell based Material Model for the single ply flexible fabric armor
Materials & Design, 2009Co-Authors: M Grujicic, G Arakere, T He, W C Bell, B A CheesemanAbstract:A meso-scale unit-cell based Material Model for a prototypical plain-woven single-ply flexible armor is developed and implemented in a Material user subroutine for use in commercial explicit finite element programs. The main intent of the Model is to attain computational efficiency when calculating the mechanical response of the multi-ply fabric-based flexible armor Material during its impact with various projectiles without significantly sacrificing the key physical aspects of the fabric microstructure, architecture and behavior. To validate the new Model, a comparative finite element method (FEM) analysis is carried out in which: (a) the plain-woven single-ply fabric is Modeled using conventional shell elements and weaving is done in an explicit manner by snaking the yarns through the fabric and (b) the fabric is treated as a planar continuum surface composed of conventional shell elements to which the new meso-scale unit-cell based Material Model is assigned. The results obtained show that the Material Model provides a reasonably good description for the fabric deformation and fracture behavior under different combinations of fixed and free boundary conditions.
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computer simulations based development of a high strain rate large deformation high pressure Material Model for stanag 4569 sandy gravel
Soil Dynamics and Earthquake Engineering, 2008Co-Authors: M Grujicic, B A Cheeseman, B Pandurangan, Nicole Coutris, W N Roy, R R SkaggsAbstract:Abstract The NATO Standard Agreement [STANAG 4569, Protection for occupants of logistics and light-armored vehicles] defines the make-up and the conditions of sandy-gravel soil which is used for testing the ability of various armor systems to provide the necessary level of protection. In this paper, an effort is made to develop a high strain-rate, large-strain, high-pressure Material Model for sandy gravel which can be used in transient non-linear dynamic simulations of the interactions between landmine detonation gaseous products, landmine-casing fragments and soil ejecta and the target military vehicles. The Material Model for sandy gravel has been developed by extending the CU–ARL sand Model [Grujicic M, Pandurangan B, Cheeseman BA, Roy WN, Skaggs RR, Gupta R. Parameterization of the porous-Material Model for sand with various degrees of water saturation. Soil Dyn Earthquake Eng 2008;28(1):20–35] in order to include the effects of gravel particles on the equation of state, strength, failure and erosion behavior. Parameterization of the sandy gravel soil Model has been done by carrying out a series of computational experiments pertaining to the deformation and fracture behavior of the two-phase (sand plus gravel) Material. Experimental tests which should be carried out in order to validate the proposed Model have been identified and described.
Janis Varna - One of the best experts on this subject based on the ideXlab platform.
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nonlinear viscoelastic viscoplastic Material Model including stiffness degradation for hemp lignin composites
Composites Science and Technology, 2008Co-Authors: Erik Marklund, Johannes Eitzenberger, Janis VarnaAbstract:Abstract In repeating tensile tests with increasing maximum strain for every loading cycle the hemp/lignin composites clearly showed a nonlinear behavior and hysteresis loops in loading and unloading. The explanation for this behavior is the inherent viscoelastic nature for this type of Material, but also noticeable stiffness degradation with increasing strain level. Creep tests performed at different stress levels revealed a nonlinear viscoelastic response and after recovery viscoplastic strain was detected for high stress levels. It is demonstrated that Schapery’s Model is suitable to Model nonlinear viscoelasticity whereas viscoplastic strain may be described by a nonlinear functional presented by Zapas and Crissman. In a creep test this functional leads to a power law with respect to time and stress. In order to include stiffness reduction due to damage Schapery’s Model has been modified by incorporating a maximum strain-state dependent function reflecting the elastic modulus reduction with increasing strain measured in tensile tests. A generalized incremental Model of the constitutive equation for viscoelastic case has been used to validate the developed Material Model in a linear stress controlled loading and unloading ramp. The Model successfully describes the main features for the investigated Material and shows good agreement with test data within the considered stress range.
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Nonlinear viscoplastic and nonlinear viscoelastic Material Model for paper fiber composites in compression
Composites Part A-applied Science and Manufacturing, 2006Co-Authors: Lars-olof Nordin, Janis VarnaAbstract:Abstract Compressive behavior of phenol–formaldehyde impregnated paper composites is studied in creep and strain recovery tests observing large nonlinear viscoelastic strains and irreversible strains, describing the latter as viscoplasticity. Stiffness reduction was not observed in experiments and therefore is not included in the Material Model. Schapery's nonlinear viscoelastic and nonlinear viscoplastic constitutive law is used as a Material Model and the stress dependent non-linearity functions are determined. First, the time and stress dependence of viscoplastic strains is described by Zapas et al. Model and identified measuring the irreversible strains after creep tests of different length at the same stress and doing the same for creep tests of a fixed length but at different stress. Then, the determination of nonlinear viscoelastic stress dependent parameters is performed.
Anastasia Muliana - One of the best experts on this subject based on the ideXlab platform.
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numerical finite element formulation of the schapery non linear viscoelastic Material Model
International Journal for Numerical Methods in Engineering, 2004Co-Authors: Rami Hajali, Anastasia MulianaAbstract:This study presents a numerical integration method for the non-linear viscoelastic behaviour of isotropic Materials and structures. The Schapery's three-dimensional (3D) non-linear viscoelastic Material Model is integrated within a displacement-based finite element (FE) environment. The deviatoric and volumetric responses are decoupled and the strain vector is decomposed into instantaneous and hereditary parts. The hereditary strains are updated at the end of each time increment using a recursive formulation. The constitutive equations are expressed in an incremental form for each time step, assuming a constant incremental strain rate. A new iterative procedure with predictor–corrector type steps is combined with the recursive integration method. A general polynomial form for the parameters of the non-linear Schapery Model is proposed. The consistent algorithmic tangent stiffness matrix is realized and used to enhance convergence and help achieve a correct convergent state. Verifications of the proposed numerical formulation are performed and compared with a previous work using experimental data for a glassy amorphous polymer PMMA. Copyright © 2003 John Wiley & Sons, Ltd.
Volker Ulbricht - One of the best experts on this subject based on the ideXlab platform.
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A nonlinear fractional viscoelastic Material Model for polymers
Computational Materials Science, 2011Co-Authors: Sebastian Müller, Markus Kästner, Jörg Brummund, Volker UlbrichtAbstract:Abstract In this contribution a test scheme based on tensile tests at different velocities, relaxation experiments and deformation controlled loading and unloading processes with intermediate relaxations has been used to experimentally characterize the nonlinear, inelastic Material behavior. Based on the experimental observations a small strain nonlinear fractional viscoelastic Material Model is derived. In order to use the Model within a finite element analysis, the constitutive equations have been generalized for the multiaxial case. The experimental test scheme and the fractional viscoelastic Material Model are subsequently applied to characterize and compute the mechanical behavior of the thermoplastic Polypropylene. After the identification of the Material parameters several uniaxial and multiaxial simulations have been carried out and compared with experimental results.
