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Author: Yazhi Zhu
Publisher:
ISBN:
Category :
Languages : en
Pages : 666
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Book Description
One of the most important limit states in structural metals is ductile fracture, and the prediction of ductile fracture is of great importance in many engineering applications. The overall objective of the research reported in this dissertation is to advance the understanding and modeling of ductile fracture in metals. This research addresses three main issues: micromechanical modeling of ductile fracture, the development of a micromechanics-based ductile fracture model and its numerical implementation, and a numerical investigation of geometry and damage induced strain localization based on a nonlocal formulation. It has long been recognized that stress triaxiality is a key parameter affecting initiation of ductile fracture. More recently, shear stress has been identified as another important parameter, in addition to stress triaxiality, that influences the process of ductile fracture. In this research, a micromechanics-based model is proposed for predicting initiation of ductile fracture that couples both stress triaxiality and shear stress. The new model is based on a combination of the existing Rice-Tracey and modified maximum shear stress models. The new model is applied to construct the fracture locus of different types of metal alloys and is used to predict fracture initiation by numerical tools. The predicted results are in good agreement with experimental data reported in literature that covers a wide range of triaxialities and shear stress. Another portion of this research, within the framework of micromechanics, investigated the effect of combined normal and shear stress components on micro-void evolution and material behavior. This work involved finite element modeling of a cubic unit cell associated with a spherical void. The results show that the void growth process and macroscopic stress-strain response is highly dependent on the shear stress component. At different ranges of triaxialities, and with different void growth and coalescence mechanisms, shear stress has an important effect on the ductile fracture process. Numerical modeling of strain localization in ductile metals based on standard continuum mechanics exhibits non-convergent mesh sensitivity. This issue is addressed in the final portion of this research. A one-dimensional model based on the nonlocal theory is proposed to analyze geometry-induced strain localization, i.e., necking in structural metals. A nonlocal continuum damage model using the same enhanced continuum law is developed to deal with the damage induced strain localization in metals. Both models provide encouraging performance in eliminating the non-convergent mesh sensitivity problem. Such improved strain localization modeling techniques show potential to be useful for further exploration of ductile fracture phenomena.
Author: Yazhi Zhu
Publisher:
ISBN:
Category :
Languages : en
Pages : 666
Get Book Here
Book Description
One of the most important limit states in structural metals is ductile fracture, and the prediction of ductile fracture is of great importance in many engineering applications. The overall objective of the research reported in this dissertation is to advance the understanding and modeling of ductile fracture in metals. This research addresses three main issues: micromechanical modeling of ductile fracture, the development of a micromechanics-based ductile fracture model and its numerical implementation, and a numerical investigation of geometry and damage induced strain localization based on a nonlocal formulation. It has long been recognized that stress triaxiality is a key parameter affecting initiation of ductile fracture. More recently, shear stress has been identified as another important parameter, in addition to stress triaxiality, that influences the process of ductile fracture. In this research, a micromechanics-based model is proposed for predicting initiation of ductile fracture that couples both stress triaxiality and shear stress. The new model is based on a combination of the existing Rice-Tracey and modified maximum shear stress models. The new model is applied to construct the fracture locus of different types of metal alloys and is used to predict fracture initiation by numerical tools. The predicted results are in good agreement with experimental data reported in literature that covers a wide range of triaxialities and shear stress. Another portion of this research, within the framework of micromechanics, investigated the effect of combined normal and shear stress components on micro-void evolution and material behavior. This work involved finite element modeling of a cubic unit cell associated with a spherical void. The results show that the void growth process and macroscopic stress-strain response is highly dependent on the shear stress component. At different ranges of triaxialities, and with different void growth and coalescence mechanisms, shear stress has an important effect on the ductile fracture process. Numerical modeling of strain localization in ductile metals based on standard continuum mechanics exhibits non-convergent mesh sensitivity. This issue is addressed in the final portion of this research. A one-dimensional model based on the nonlocal theory is proposed to analyze geometry-induced strain localization, i.e., necking in structural metals. A nonlocal continuum damage model using the same enhanced continuum law is developed to deal with the damage induced strain localization in metals. Both models provide encouraging performance in eliminating the non-convergent mesh sensitivity problem. Such improved strain localization modeling techniques show potential to be useful for further exploration of ductile fracture phenomena.
Author: Bradley Dodd
Publisher: Academic Press
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 328
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Book Description
Author: P. F. Thomason
Publisher: Pergamon
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 240
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Book Description
An account of the recent developments in research into ductile fracture in metals and alloys. Aspects covered include localized fracture at the root of notches and sharp cracks, and fracture in bulk plastic-deformation processes of the metal and metal forming type. Also discusses various theoretical
Author: Christopher M. Smith
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Fracture in steel structures represents a critical limit state in evaluating the safety and resiliency of civil infrastructure during earthquakes. This importance was demonstrated by the widespread fractures observed in older steel connections during the 1994 Northridge Earthquake, and in modern connections during the 2011 Christchurch Earthquake. The application of traditional crack-tip fracture mechanics to structural design provisions has successfully delayed the onset of Northridge-type brittle fracture. However, the extreme strain capacity in modern ductile connections increases the relevance of ductile fracture. Recent developments in 'local' fracture models have proven successful at predicting ductile fracture under many conditions. However, the application of these models has been limited due to their limited scope and difficulty in evaluation of the necessary continuum parameters. The current objective in the structural engineering community of replacing full-scale experiments with advanced finite element simulations require accurate models and calibration techniques to evaluate cyclic plasticity and fracture predictions. Motivated by the above requirements, the objectives of the present study are to (1) further the understanding of the ductile fracture mechanism for all stress, (2) develop robust methods for the calibration of constitutive parameters and local fracture models in highly plastic materials, and (3) to develop a new damage-based model to predict ductile fracture under all relevant structural conditions states (especially those with low stress triaxiality). These objectives are accomplished through an extensive experimental program, including 48 monotonic and cyclic specimens in geometries designed to effectively interrogate the fracture criteria. A total of six specimen designs are tested, including three original designs developed for the current study. Complementary finite element analyses are used to evaluate the local fracture criteria, and micrographic examination and void cell simulations provide insight into the fracture mechanism at varying stress states. The data from these experiments and the derived fracture model demonstrate the importance of the deviatoric stress state, in addition to the hydrostatic pressure, in the fracture ductility of steel. Specifically, material in a plane strain condition is found to exhibit about 50\% more fracture ductility than material in an axisymmetric stress condition. Through meta-analysis of test data from this and previous studies, ductile fracture is found to be prohibited under negative (compressive) hydrostatic pressure.
Author: Elisabeth Bouchaud
Publisher: Springer Science & Business Media
ISBN: 9401006563
Category : Science
Languages : en
Pages : 369
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Book Description
The main scope of this Cargese NATO Advanced Study Institute (June 5-17 2000) was to bring together a number of international experts, covering a large spectrum of the various Physical Aspects of Fracture. As a matter of fact, lecturers as well as participants were coming from various scientific communities: mechanics, physics, materials science, with the common objective of progressing towards a multi-scale description of fracture. This volume includes papers on most materials of practical interest: from concrete to ceramics through metallic alloys, glasses, polymers and composite materials. The classical fields of damage and fracture mechanisms are addressed (critical and sub-critical quasi-static crack propagation, stress corrosion, fatigue, fatigue-corrosion . . . . as well as dynamic fracture). Brittle and ductile fractures are considered and a balance has been carefully kept between experiments, simulations and theoretical models, and between the contributions of the various communities. New topics in damage and fracture mechanics - the effect of disorder and statistical aspects, dynamic fracture, friction and fracture of interfaces - were also explored. This large overview on the Physical Aspects of Fracture shows that the old barriers built between the different scales will soon "fracture". It is no more unrealistic to imagine that a crack initiated through a molecular dynamics description could be propagated at the grain level thanks to dislocation dynamics included in a crystal plasticity model, itself implemented in a finite element code. Linking what happens at the atomic scale to fracture of structures as large as a dam is the new emerging challenge.
Author: P. Suquet
Publisher: Springer
ISBN: 3709126622
Category : Technology & Engineering
Languages : en
Pages : 352
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Book Description
This book presents the most recent progress of fundamental nature made in the new developed field of micromechanics: transformation field analysis, variational bounds for nonlinear composites, higher-order gradients in micromechanical damage models, dynamics of composites, pattern based variational bounds.
Author: Liang-Jiu Jia
Publisher: Springer
ISBN: 9811326614
Category : Science
Languages : en
Pages : 231
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Book Description
This book presents experimental results and theoretical advances in the field of ultra-low-cycle fatigue failure of metal structures under strong earthquakes, where the dominant failure mechanism is ductile fracture. Studies on ultra-low-cycle fatigue failure of metal materials and structures have caught the interest of engineers and researchers from various disciplines, such as material, civil and mechanical engineering. Pursuing a holistic approach, the book establishes a fundamental framework for this topic, while also highlighting the importance of theoretical analysis and experimental results in the fracture evaluation of metal structures under seismic loading. Accordingly, it offers a valuable resource for undergraduate and graduate students interested in ultra-low-cycle fatigue, researchers investigating steel and aluminum structures, and structural engineers working on applications related to cyclic large plastic loading conditions.
Author: Alphose Zingoni
Publisher: CRC Press
ISBN: 1317280628
Category : Technology & Engineering
Languages : en
Pages : 3395
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Book Description
Insights and Innovations in Structural Engineering, Mechanics and Computation comprises 360 papers that were presented at the Sixth International Conference on Structural Engineering, Mechanics and Computation (SEMC 2016, Cape Town, South Africa, 5-7 September 2016). The papers reflect the broad scope of the SEMC conferences, and cover a wide range of engineering structures (buildings, bridges, towers, roofs, foundations, offshore structures, tunnels, dams, vessels, vehicles and machinery) and engineering materials (steel, aluminium, concrete, masonry, timber, glass, polymers, composites, laminates, smart materials). Some contributions present the latest insights and new understanding on (i) the mechanics of structures and systems (dynamics, vibration, seismic response, instability, buckling, soil-structure interaction), and (ii) the mechanics of materials and fluids (elasticity, plasticity, fluid-structure interaction, flow through porous media, biomechanics, fracture, fatigue, bond, creep, shrinkage). Other contributions report on (iii) recent advances in computational modelling and testing (numerical simulations, finite-element modeling, experimental testing), and (iv) developments and innovations in structural engineering (planning, analysis, design, construction, assembly, maintenance, repair and retrofitting of structures). Insights and Innovations in Structural Engineering, Mechanics and Computation is particularly of interest to civil, structural, mechanical, marine and aerospace engineers. Researchers, developers, practitioners and academics in these disciplines will find the content useful. Short versions of the papers, intended to be concise but self-contained summaries of the full papers, are collected in the book, while the full versions of the papers are on the accompanying CD.
Author: F. C. Campbell
Publisher: ASM International
ISBN: 1615039767
Category : Technology & Engineering
Languages : en
Pages : 699
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Book Description
"This book emphasizes the physical and practical aspects of fatigue and fracture. It covers mechanical properties of materials, differences between ductile and brittle fractures, fracture mechanics, the basics of fatigue, structural joints, high temperature failures, wear, environmentally-induced failures, and steps in the failure analysis process."--publishers website.
Author: D.S. Wilkinson
Publisher: Elsevier
ISBN: 1483286789
Category : Technology & Engineering
Languages : en
Pages : 329
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Book Description
This International Symposium is sponsored by the Materials Engineering Section and the Basic Sciences Section of the Metallurgical Society of CIM and co-sponsored by the Canadian Ceramic Society. Topics covered include metal matrix composites, structural ceramics, polymeric composite materials, powder metallurgical materials and interfaces.
