Sequential slip transfer across grain boundaries (GB) has an important role in size-dependent propagation of plastic deformation in polycrystalline metals. For example, the Hall–Petch effect, which states that a smaller average grain size... more
Sequential slip transfer across grain boundaries (GB) has an important role in size-dependent propagation of plastic deformation in polycrystalline metals. For example, the Hall–Petch effect, which states that a smaller average grain size results in a higher yield stress, can be rationalised in terms of dislocation pile-ups against GBs. In spite of extensive studies in modelling individual phases and grains using atomistic simulations, well-accepted criteria of slip transfer across GBs are still lacking, as well as models of predicting irreversible GB structure evolution. Slip transfer is inherently multiscale since both the atomic structure of the boundary and the long-range fields of the dislocation pile-up come into play. In this work, concurrent atomistic-continuum simulations are performed to study sequential slip transfer of a series of curved dislocations from a given pile-up on Σ3 coherent twin boundary (CTB) in Cu and Al, with dominant leading screw character at the site of...
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This study compares the views on spirituality of dually diagnosed patients (diagnosed with both substance abuse and general psychiatric disorders) and medical students in order to investigate their respective orientations toward... more
This study compares the views on spirituality of dually diagnosed patients (diagnosed with both substance abuse and general psychiatric disorders) and medical students in order to investigate their respective orientations toward spirituality and their views of the importance of spirituality in the treatment of addiction. We administered a modified version of Feagin's "Orientation to Life and God Scale" to assess religious and spiritual orientation in both the patients and students. A second series of items was developed and administered in order to compare the patients' and students' perceptions of the relative importance of a religious and spiritual orientation in substance abuse treatment. A third series of items was also given to compare the nature of religious and health-related services on the inpatient unit that patients and students most wanted to see improved. We found that the medical students responsible for treating substance abuse are significantly less religiously and spirituality oriented than the patients they treat, and that the students do not indicate that spirituality is an important component in the care of these patients. It may be clinically relevant to train medical students in the potential importance of spirituality in addiction treatment so that they can incorporate spirituality into the treatment of addictions.
Research Interests: Religion, Psychology, Medical Education, Culture, Religion and medicine, and 15 moreMedicine, Drug, Curriculum, Medical Students, Humans, Female, Male, Recovery, Drug Addiction, Attitude, Mental Disorders, Adult, Public health systems and services research, Reproducibility of Results, and professional patient relations
In this paper, we consider the problem of selecting the most appropriate model from many possible models to describe datasets involving mixtures of distributions. The proposed method consists of finding the maximum likelihood estimators... more
In this paper, we consider the problem of selecting the most appropriate model from many possible models to describe datasets involving mixtures of distributions. The proposed method consists of finding the maximum likelihood estimators (MLEs) of different assumed mixture models that describe a dataset, using the Expectation-Maximization (EM) algorithm, and subsequently using bootstrap sampling technique to identify the distance between the empirical cumulative distribution function (cdf) of the dataset and the MLE fitted cdf. To test the goodness of fit, a new metric, the Integrated Cumulative Error (ICE) is proposed and compared with other existing metrics for accuracy of detecting the appropriate model. The ICE metric shows a markedly improved performance, from the existing metrics, in identifying the correct 1 mixture model. The method is applied to model the distribution of indicators of the fatigue crack formation potency, obtained from numerical experiments.
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Multilevel design is a subset of engineering design in which design problems are defined and analyzed at various levels of model complexity or resolution. Due to the potential for propagated uncertainty in a multilevel design process,... more
Multilevel design is a subset of engineering design in which design problems are defined and analyzed at various levels of model complexity or resolution. Due to the potential for propagated uncertainty in a multilevel design process, design goals for maximizing system robustness to uncertainty in noise and control factors are included in the Blast resistant panels (BRP) design process. Blast resistant panels (BRPs) are sandwich structures consisting of two solid panels surrounding a honeycomb core. Under impulse loading, BRPs experience less deflection than similarly loaded solid panels of equal mass due to core crushing. In order to manage complexity in BRP concurrent product and materials design, a multilevel design approach is proposed. Additionally, in order to collect and store BRP design information in a modular and reusable format, a template-based design approach is implemented in BRP multilevel design. In this paper, a generic multilevel design template based on existing d...
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... Furthermore, experiments have indicated that the coefficients of the direct hardening and dynamic recovery terms are ratedependent (MCDOWELL et al.. ... WALKER, 1981 ; CHABOCHE, 1987; LOWE and MILLER, 1986; ROBINSON, 1978; HART, 1976;... more
... Furthermore, experiments have indicated that the coefficients of the direct hardening and dynamic recovery terms are ratedependent (MCDOWELL et al.. ... WALKER, 1981 ; CHABOCHE, 1987; LOWE and MILLER, 1986; ROBINSON, 1978; HART, 1976; BODNER and PARTOM. ...
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Significant advances have been realized in accelerating the insertion of new and improved materials into products within the compressed timeframe of design and prototyping using the emerging computational materials science modeling and... more
Significant advances have been realized in accelerating the insertion of new and improved materials into products within the compressed timeframe of design and prototyping using the emerging computational materials science modeling and systems-based information management and materials design strategies. Recent initiatives in the USA to strengthen the link between materials modeling and simulation, process route, and structure–property relations are discussed, with emphasis on the Accelerated Insertion of Materials (AIM) strategy, tools, and methods. The recent emphasis on Integrated Computational Materials Engineering (ICME), an emergent branch of AIM that is built upon integrating modeling and simulation with product development, is discussed in terms of its common ground with the notion of concurrent design of materials and products– materials design. Materials design includes multiscale modeling of hierarchical materials as an important component, but is much broader in scope. This distinction between materials design and multiscale modeling is considered in some detail, with emphasis on top-down requirements on material structure and performance to meet product requirements. Uncertainty is a ubiquitous aspect of materials design, regardless of whether design decisions are informed by experimental measurements, modeling, and simulation or other heuristics. Some emerging concepts for robust design of materials are briefly described, and challenges for the synthesis of modeling and simulation and materials design are outlined.
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We consider the role of computational materials science and mechanics in establishing improved understanding and quantification of structure-property relations for engineered materials. This chapter first addresses key aspects and... more
We consider the role of computational materials science and mechanics in establishing improved understanding and quantification of structure-property relations for engineered materials. This chapter first addresses key aspects and implications of structure hierarchy in practical systems of interest. We then proceed to discuss aspirations and challenges for designing materials via tailoring of hierarchical structure. It is emphasized that materials design is not equivalent to modeling across scales of material structure hierarchy; the latter provides support for decisions made in design and development of materials in the presence of uncertainty. We next provide compelling reasons to develop microstructure-sensitive multiscale models to facilitate simulation-assisted alloy design. Hierarchical and concurrent multiscale models are defined and contrasted in terms of utility in supporting materials design. Inherent difficulties of inverting complex structure-property relations are discussed, along with some recently developed strategies for relating desired properties to feasible structures, as well as top-down, inductive design exploration.
The diffusion of hydrogen in metals is of interest due to the deleterious influence of hydrogen on material ductility and fracture resistance. It is becoming increasingly clear that hydrogen transport couples significantly with... more
The diffusion of hydrogen in metals is of interest due to the deleterious influence of hydrogen on material ductility and fracture resistance. It is becoming increasingly clear that hydrogen transport couples significantly with dislocation activity. In this work, we use a coupled diffusion-crystal plasticity model to incorporate hydrogen transport associated with dislocation sweeping and pipe diffusion in addition to standard lattice diffusion. Moreover, we consider generation of vacancies via plastic deformation and stabilization of vacancies via trapping of hydrogen. The proposed hydrogen transport model is implemented in a physically based crystal viscoplasticity framework to model the interaction of dislocation substructure and hydrogen migration. In this study, focus is placed on hydrogen transport and trapping within the intense deformation field of a crack tip plastic zone. We discuss the implications of the model results in terms of constitutive relations that incorporate hy...
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... of the constant amplitude, completely reversed uniaxial strain-and stress-life plots for a low ... might be clustered and hence their interaction may affect the non-local maximum plastic ... Hence parametric studies are conducted to... more
... of the constant amplitude, completely reversed uniaxial strain-and stress-life plots for a low ... might be clustered and hence their interaction may affect the non-local maximum plastic ... Hence parametric studies are conducted to determine the nonlocal maximum plastic shear strain ...
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This chapter considers advances over the past 15 years achieved by the authors and coworkers on generalized crystal plasticity to address size and configuration effects in dislocation plasticity at the micron scale. The specific... more
This chapter considers advances over the past 15 years achieved by the authors and coworkers on generalized crystal plasticity to address size and configuration effects in dislocation plasticity at the micron scale. The specific approaches addressed here focus on micropolar and micromorphic theories rather than adopting strain gradient theory as the starting point, as motivated by the pioneering ideas of Eringen (Eringen and Suhubi 1964; Eringen and Claus Jr 1969; Eringen 1999). It is demonstrated with examples that for isotropic elasticity and specific sets of slip systems, a dislocation-based formulation of micropolar or micromorphic type provides results comparable to discrete dislocation dynamics and has much in common with the structure of Gurtin’s slip gradient theory (Gurtin 2002; Gurtin et al. 2007).
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The various scales of hierarchical structures of metallic materials range from nm to mm. The notion of crystalline plasticity modeling is generalized to a set of model constructs that address phenomena associated with evolution of... more
The various scales of hierarchical structures of metallic materials range from nm to mm. The notion of crystalline plasticity modeling is generalized to a set of model constructs that address phenomena associated with evolution of dislocations in crystals across a range of corresponding length scales, with time scales ranging from fs to years. These model constructs include coarse-grained atomistic modeling (atomistics), microscopic phase field models, dislocation field models, discrete dislocation dynamics, statistical continuum dislocation models, and mesoscale generalized continuum models of gradient, micropolar or micromorphic type, as well as local continuum crystal plasticity that can be applied to polycrystals. We identify key phenomena of lattice dislocations and discuss how these are mapped onto the capabilities of various scale-specific model constructs. Concurrent and hierarchical multiscale model transitions in space and time are discussed, distinguishing between coarse-graining and spatial domain decomposition approaches for lower scale models. We focus on model order reduction methods for mesoscale to macroscale constructs. In terms of bridging scales, the practical importance of two-scale transitions between models of differing fidelity and/or resolution is emphasized, whether of concurrent or hierarchical nature. Various scale-specific models for crystalline plasticity are considered, along with examples. The chapter closes by summarizing some of the long-standing gaps in modeling dislocation plasticity in crystals and polycrystals.
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The notion of crystalline plasticity model constructs is generalized to address different levels of material structure hierarchy, extending from predictive atomic scale approaches through responses of polycrystals. Intermediate forms of... more
The notion of crystalline plasticity model constructs is generalized to address different levels of material structure hierarchy, extending from predictive atomic scale approaches through responses of polycrystals. Intermediate forms of models vary from discrete (and often dynamic) methods to statistical and continuum methods. These range from coarse-grained atomistic and microscopic phase field models, discrete dislocation dynamics, dislocation field mechanics, statistical continuum dislocation, and mesoscopic phase field models to mesoscale generalized continuum models of gradient or micropolar type and on up to grain-scale continuum crystal plasticity. Essential elements of crystalline plasticity are listed, and it is argued that no single model construct addresses all elements. Hence, a portfolio of distinct model constructs is necessary to support design of hierarchically structured materials, in some cases demanding atomic scale resolution and in others cooperative behavior of grains at scales 4–5 orders of magnitude larger. Some recent progress in addressing key gaps in crystalline plasticity models is discussed, including distinguishing nucleation and growth processes, slip transfer at interfaces, the need for more robust submicron generalized continua frameworks, and decision support for quantifying extreme value responses and properties that are controlled by dislocation plasticity.
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... Show full item record. Please use this identifier to cite or link to this item: http://hdl.handle.net/ 1853/20500. Title: Creep crack growth behavior of aluminum alloy 2519-T87. Author: Hamilton,Benjamin Carter. Type: Thesis. URI:... more
... Show full item record. Please use this identifier to cite or link to this item: http://hdl.handle.net/ 1853/20500. Title: Creep crack growth behavior of aluminum alloy 2519-T87. Author: Hamilton,Benjamin Carter. Type: Thesis. URI: http://hdl.handle.net/1853/20500. Date: Dec-1994. ...
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Many practical problems of interest deal with irreversible, path dependent aspects of material behavior, such as hysteresis due to plastic deformation or phase transition, fatigue and fracture, or diffusive rearrangement. Some of these... more
Many practical problems of interest deal with irreversible, path dependent aspects of material behavior, such as hysteresis due to plastic deformation or phase transition, fatigue and fracture, or diffusive rearrangement. Some of these processes occur so slowly and so near equilibrium that attendant models forego description of nonequilibrium aspects of dissipation (e.g., grain growth). On the other hand, some irreversible behaviors such as thermally activated dislocation glide can occur farther from equilibrium with a spectrum of relaxation times. The fact that quasi-stable, nonequilibrium configurations of defects can exist in lattices at multiple length scales, combined with the long range nature of interaction forces, presents an enormous challenge to the utility of high fidelity, high degree of freedom (DoF) dynamical models that employ atomistic or molecular modeling methods. For example, analyses of simple crystal structures using molecular dynamics have now reached scales on the order of microns, but are limited to rather idealized systems such as pure metals and to small time durations of the order of nanoseconds. High fidelity analyses of generation, motion and interaction of line defects in lattices based on discrete dislocation dynamics, making use of interactions based on linear elastic solutions, cover somewhat higher length scales and longer time scales, but are also limited in considering realistic multiphase, hierarchical microstructures. Crystal plasticity as well cannot be used for large scale finite element simulations, for example, crash simulations of a vehicle into a barrier.
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There is increasing awareness of the imperative to accelerate materials discovery, design, development, and deployment. Materials design is essentially a goal-oriented activity that views the material as a complex system of interacting... more
There is increasing awareness of the imperative to accelerate materials discovery, design, development, and deployment. Materials design is essentially a goal-oriented activity that views the material as a complex system of interacting subsystems with models and experiments at multiple scales of materials structure hierarchy. The goal of materials design is effectively to invert quantitative relationships between process path, structure, and materials properties or responses to identify feasible materials. We first briefly discuss challenges in framing process-structure-property relationships for materials and the critical role of quantifying uncertainty and tracking its propagation through analysis and design. A case study exploiting inductive design of ultrahigh-performance concrete is briefly presented. We focus on important recent directions and key scientific challenges regarding the highly collaborative intersections of materials design with systems engineering, uncertainty qu...
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Traditionally, design engineers and materials scientists have adopted very different approaches. Natural scientists are concerned with building a body of knowledge about objects or phenomena—their characteristics, behavior, and... more
Traditionally, design engineers and materials scientists have adopted very different approaches. Natural scientists are concerned with building a body of knowledge about objects or phenomena—their characteristics, behavior, and interactions. Designers, on the other hand, are concerned with how to synthesize and realize artifacts that have desired properties or functionality and fulfill a purpose or attain a goal [1]. Primarily, new materials have been developed with empirical, trial-and-error techniques prominent in the natural ...
Research Interests: Engineering and Design
Research Interests: Engineering, Materials Science, Heat Transfer, Linear Elasticity, Finite Elements, and 14 moreTopology Optimization, Finite Element, Pavement design and analysis, Cellular material, Materials Design, Structure Analysis, Functionally Graded, Seismic analysis and design, Temperature Dependence, Convective Heat Transfer, Constitutive Equation, Cell Size, optimal algorithm, and Solids and Structures
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A physically realistic macroscopic decomposition of the deformation gradient for metallic polycrystals should explicitly account for all relevant sub-macroscopic kinematic processes, including lattice deformation, plastic flow, and... more
A physically realistic macroscopic decomposition of the deformation gradient for metallic polycrystals should explicitly account for all relevant sub-macroscopic kinematic processes, including lattice deformation, plastic flow, and evolution of damage, that significantly contribute to the homogenized deformation at the macroscale. The present work suggests such a decomposition, based on principles of volume averaging and focusing upon elastoplasticity and a variety
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The effects of microstructure on the development and growth of small fatigue cracks in structural components play a strong role in dictating the class of mechanics approaches which are most viable in their treatment. The development of... more
The effects of microstructure on the development and growth of small fatigue cracks in structural components play a strong role in dictating the class of mechanics approaches which are most viable in their treatment. The development of multiple small crack embryos associated with distributed cyclic plastic strain processes motivates a Continuum Damage Mechanics (CDM) description rather than a fracture mechanics treatment. The influence of material heterogeneity and the proximity to the free surface on the fatigue process in wrought alloys is significant and must be addressed in CDM. Sequential processes of early crack growth past heterogeneously distributed microstructural barriers, small crack coalescence and propagation of a dominant flow must be addressed through a consistent scheme which identifies damage driving forces as well as accessible propagation paths through the microstructure. Size effects in fatigue are related to the accessibility of low resistance microstructure pat...
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A general constitutive framework is presented for rate-independent porous plasticity. This framework is formulated using combined nonlinear isotropic-kinematic hardening rules along with void growth models which can be either implicitly... more
A general constitutive framework is presented for rate-independent porous plasticity. This framework is formulated using combined nonlinear isotropic-kinematic hardening rules along with void growth models which can be either implicitly embedded within a pressure dependent yield function or explicitly established based on a micromechanical model. A void nucleation criterion is also introduced in the framework. An associative flow rule is first set forth which implicitly introduces general void growth models. Correlations are presented with experimentally determined porosity evolution in circumferentially notched specimens subjected to various superimposed hydrostatic pressures. The framework is then generalized to include explicit void growth models with plastic flow which are either associative or non-associative with the yield function. Single element computations are carried out using these model frameworks to compare the behavior predicted by specific implicit and explicit void ...
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In this paper, we analyze a metal honeycomb sandwich beam/torsion bar subjected to combined loading conditions. The cell wall arrangement of the honeycomb core is addressed in the context of maximizing resistance to either bending,... more
In this paper, we analyze a metal honeycomb sandwich beam/torsion bar subjected to combined loading conditions. The cell wall arrangement of the honeycomb core is addressed in the context of maximizing resistance to either bending, torsion, or combined bending and torsion for given dimensions, face sheet thicknesses and core relative density. It is found that the relative contributions of the honeycomb core to torsion and bending resistances are sensitive to the configuration of cell walls and the optimal properties significantly exceed those of stochastic metallic foams as sandwich beam core materials for this configuration.
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A generalized continuum representation of two-dimensional periodic cellular solids is obtained by treating these materials as micropolar continua. Linear elastic micropolar constants are obtained using an energy approach for square,... more
A generalized continuum representation of two-dimensional periodic cellular solids is obtained by treating these materials as micropolar continua. Linear elastic micropolar constants are obtained using an energy approach for square, equilateral triangular, mixed triangle and diamond ...
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This conference was international and balanced in scope, as witnessed by the presentation of over 20 papers addressing the following topics: (1) Elastic-Plastic Fracture; (2) Three-Dimensional Cracks; (3) Anisotropic Fracture and... more
This conference was international and balanced in scope, as witnessed by the presentation of over 20 papers addressing the following topics: (1) Elastic-Plastic Fracture; (2) Three-Dimensional Cracks; (3) Anisotropic Fracture and Applications; (4) Fracture of Composite Materials; (5) Mixed-Mode Fracture Toughness; (6) Mixed-Mode Fatigue Crack Growth; and (7) Experimental Studies in Mixed-Mode Fatigue and Fracture. Separate abstracts were prepared for
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Abstract The number of cycles required to form and grow microstructurally small fatigue cracks in metals exhibits substantial variability, particularly for low applied strain amplitudes. This variability is commonly attributed to the... more
Abstract The number of cycles required to form and grow microstructurally small fatigue cracks in metals exhibits substantial variability, particularly for low applied strain amplitudes. This variability is commonly attributed to the heterogeneity of cyclic plastic deformation within the microstructure, and presents a challenge to minimum life design of fatigue resistant components. This paper analyzes sources of variability that contribute to the driving force of transgranular fatigue cracks within nucleant grains. We employ crystal plasticity finite element simulations that explicitly render the polycrystalline microstructure and Fatigue Indicator Parameters (FIPs) averaged over different volume sizes and shapes relative to the anticipated fatigue damage process zone. Volume averaging is necessary to both achieve description of a finite fatigue damage process zone and to regularize mesh dependence in simulations. Results from constant amplitude remote applied straining are characterized in terms of the extreme value distributions of volume averaged FIPs. Grain averaged FIP values effectively mitigate mesh sensitivity, but they smear out variability within grains. Volume averaging over bands that encompass critical transgranular slip planes appear to present the most attractive approach to mitigate mesh sensitivity while preserving variability within grains.
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Abstract A microcrack propagation approach is developed for creep-fatigue-oxidation interaction. The approach permits treatment of fatigue crack'initiation'and propagation within the same conceptual framework. Good correlation... more
Abstract A microcrack propagation approach is developed for creep-fatigue-oxidation interaction. The approach permits treatment of fatigue crack'initiation'and propagation within the same conceptual framework. Good correlation is achieved for high temperature and ...