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Understanding and quantifying correctly the effects of overload on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multstage fatigue model under variable loading. Micromechanical... more
Understanding and quantifying correctly the effects of overload on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multstage fatigue model under variable loading. Micromechanical simulations were conducted on a 7075-T651 Al alloy ...
A quantitative approach is presented to evaluate the uncertainty of a microstructurebased multistage fatigue (MSF) model for fatigue life predictions and fatigue damage estimations. The microstructurally-based MSF model manifests the... more
A quantitative approach is presented to evaluate the uncertainty of a microstructurebased multistage fatigue (MSF) model for fatigue life predictions and fatigue damage estimations. The microstructurally-based MSF model manifests the varying mechanisms of fatigue damage ...
Uncertainties in material microstructure features can lead to variability in damage predictions based on multiscale microstructure-property models. In this paper, we present an analytical approach for uncertainty analysis by combining a... more
Uncertainties in material microstructure features can lead to variability in damage predictions based on multiscale microstructure-property models. In this paper, we present an analytical approach for uncertainty analysis by combining a dimension reduction technique for evaluation of ...
Abstract: In this study, the authors use a physically-motivated internal state variable plasticity/damage model containing a mathematical length scale to represent the material behavior in finite element (FE) simulations of a large scale... more
Abstract: In this study, the authors use a physically-motivated internal state variable plasticity/damage model containing a mathematical length scale to represent the material behavior in finite element (FE) simulations of a large scale boundary value problem. This ...
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... Balasundaram, A., Shan, Z., Gokhale, AM, Graham, S., and Horstemeyer, MF, Particle Rotations During Plastic Deformation of 5086 (O) Aluminum ... Horstemeyer, MF and Ramaswamy, S., On Factors Affecting Localization and Void Growth in... more
... Balasundaram, A., Shan, Z., Gokhale, AM, Graham, S., and Horstemeyer, MF, Particle Rotations During Plastic Deformation of 5086 (O) Aluminum ... Horstemeyer, MF and Ramaswamy, S., On Factors Affecting Localization and Void Growth in Ductile Metals: A Parametric Study, Int ...
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... Previous work by Horstemeyer and Ramaswamy [27] and more recent computational work by Fabregue and Pardoen [11] showed that the void nucleation and growth from secondary voids affected the coalescence of the primary voids. ...
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... al., 1979). The Bauschinger effect has been found to be a function of several parameters (loading path, strain rate, temperature and texture) ([Ono et al., 1983], [Arsenault and Wu, 1987] and [Thakur et al., 1996]). The physical ...
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Finite element analyses are frequently used to model growing fatigue cracks and the associated plasticity-induced crack closure. A new methodology is presented to calculate crack opening values in planar geometries using the crack surface... more
Finite element analyses are frequently used to model growing fatigue cracks and the associated plasticity-induced crack closure. A new methodology is presented to calculate crack opening values in planar geometries using the crack surface nodal force distribution under minimum loading as determined from finite element analyses. The calculated crack opening values are compared with values obtained using finite element analysis and more conventional crack opening assessment methodologies, which focus on a single node near the crack tip. The new method eliminates the need to arbitrarily select a single node when defining the opening load or stress.
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In BCC crystals, such as Tungsten (W), slippage has been observed on the (110) and (112) planes. In this work, hydrogen diffusion paths from three different W surfaces ((100),(110) and (112)) have been calculated using first principles... more
In BCC crystals, such as Tungsten (W), slippage has been observed on the (110) and (112) planes. In this work, hydrogen diffusion paths from three different W surfaces ((100),(110) and (112)) have been calculated using first principles density functional theory. ...
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ABSTRACT The presence of softening in the Bammann-Chiesa-Johnson (BCJ) material model presents a major physical drawback: the unlimited localization of strain which results in spurious zero dissipated energy at failure. This difficulty... more
ABSTRACT The presence of softening in the Bammann-Chiesa-Johnson (BCJ) material model presents a major physical drawback: the unlimited localization of strain which results in spurious zero dissipated energy at failure. This difficulty resolves when the BCJ model ...
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ABSTRACT We used a physically motivated internal state variable plasticity/damage model containing a mathematical length scale to idealize the material response in finite element simulations of a large-scale boundary value problem. The... more
ABSTRACT We used a physically motivated internal state variable plasticity/damage model containing a mathematical length scale to idealize the material response in finite element simulations of a large-scale boundary value problem. The problem consists of a moving striker colliding against a stationary hazmat tank car. The motivations are (1) to reproduce with high fidelity finite deformation and temperature histories, damage, and high rate phenomena that may arise during the impact accident and (2) to address the material postbifurcation regime pathological mesh size issues. We introduce the mathematical length scale in the model by adopting a nonlocal evolution equation for the damage, as suggested by Pijaudier-Cabot and Bazant in the context of concrete. We implement this evolution equation into existing finite element subroutines of the plasticity/failure model. The results of the simulations, carried out with the aid of Abaqus/Explicit finite element code, show that the material model, accounting for temperature histories and nonlocal damage effects, satisfactorily predicts the damage progression during the tank car impact accident and significantly reduces the pathological mesh size effects.
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ABSTRACT We present a set of Python routines to perform basic tests of classical atomistic potentials and their example applications. These routines are implemented using universal Atomic Simulation Environment (ASE) and LAMMPS molecular... more
ABSTRACT We present a set of Python routines to perform basic tests of classical atomistic potentials and their example applications. These routines are implemented using universal Atomic Simulation Environment (ASE) and LAMMPS molecular dynamics code. ASE is utilized to create atomic configurations, to write input scripts for LAMMPS, and to read results from output files. Evaluated properties are formation energies and volumes of simple point defects (vacancies, substitutions, and interstitials), formation energies of basic surfaces, heats of formation of simple binary compounds, and elastic constants. The flexibility of LAMMPS allows easy switching between different semi-empirical potentials, while the universality of ASE allows to compare results with a variety of electronic structure codes.
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Understanding and quantifying the effects of overloads/overstrains on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multistage fatigue model under variable amplitude loading.... more
Understanding and quantifying the effects of overloads/overstrains on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multistage fatigue model under variable amplitude loading. Micromechanical simulations are conducted on a 7075-T651 ...
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ABSTRACT The Bammann, Chiesa, and Johnson (BCJ) material model predicts unlimited localization of strain and damage, resulting in a zero dissipation energy at failure. This difficulty resolves when the BCJ model is modified to incorporate... more
ABSTRACT The Bammann, Chiesa, and Johnson (BCJ) material model predicts unlimited localization of strain and damage, resulting in a zero dissipation energy at failure. This difficulty resolves when the BCJ model is modified to incorporate a nonlocal evolution equation for the damage, as proposed by Pijaudier-Cabot and Bazant (1987, "Nonlocal Damage Theory," ASCE J. Eng. Mech., 113, pp. 1512-1533.). In this work, we theoretically assess the ability of such a modified BCJ model to prevent unlimited localization of strain and damage. To that end, we investigate two localization problems in nonlocal BCJ metals: appearance of a spatial discontinuity of the velocity gradient in any finite, inhomogeneous body, and localization of the dissipation energy into finite bands. We show that in spite of the softening arising from the damage, no spatial discontinuity occurs in the velocity gradient. Also, we find that the dissipation energy is continuously distributed in nonlocal BCJ metals and therefore cannot localize into zones of vanishing volume. As a result, the appearance of any vanishing width adiabatic shear band is impossible in a nonlocal BCJ metal. Finally, we study the finite element (FE) solution of shear banding in a rectangular plate, deformed in plane strain tension and containing an imperfection, thereby illustrating the effects of imperfections and finite size on the localization of strain and damage.
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Int. J. Vehicle Design, Vol. 54, No. 4, 2010 ... Shape and sizing optimisation of automotive structures with deterministic and probabilistic design constraints ... Center for Advanced Vehicular Systems, Department of Aerospace... more
Int. J. Vehicle Design, Vol. 54, No. 4, 2010 ... Shape and sizing optimisation of automotive structures with deterministic and probabilistic design constraints ... Center for Advanced Vehicular Systems, Department of Aerospace Engineering, Mississippi State University, Mississippi ...
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Understanding and quantifying the effects of overloads/overstrains on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multistage fatigue model under variable amplitude loading.... more
Understanding and quantifying the effects of overloads/overstrains on the cyclic damage accumulation at a microscale discontinuity is essential for the development of a multistage fatigue model under variable amplitude loading. Micromechanical simulations are conducted on a 7075-T651 ...
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In BCC crystals, such as Tungsten (W), slippage has been observed on the (110) and (112) planes. In this work, hydrogen diffusion paths from three different W surfaces ((100),(110) and (112)) have been calculated using first principles... more
In BCC crystals, such as Tungsten (W), slippage has been observed on the (110) and (112) planes. In this work, hydrogen diffusion paths from three different W surfaces ((100),(110) and (112)) have been calculated using first principles density functional theory. ...
