A Study of Ductile Fracture Prediction in Microforming Process PDF Download

Author: Jiaqi Ran
Publisher:
ISBN:
Category : Fracture mechanics
Languages : en
Pages : 296

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Author: Kazutake Komori
Publisher: Academic Press
ISBN: 0128147733
Category : Technology & Engineering
Languages : en
Pages : 294

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Book Description
Ductile Fracture in Metal Forming: Modeling and Simulation examines the current understanding of the mechanics and physics of ductile fracture in metal forming processes while also providing an approach to micromechanical ductile fracture prediction that can be applied to all metal forming processes. Starting with an overview of different ductile fracture scenarios, the book then goes on to explain modeling techniques that predict a range of mechanical phenomena that can lead to ductile fracture. The challenges in creating micromechanical models are addressed alongside methods of applying these models to several common metal forming processes. This book is suitable for researchers working in mechanics of materials, metal forming, mechanical metallurgy, and plasticity. Engineers in R&D industries involved in metal forming such as manufacturing, aerospace, and automation will also find the book very useful. Explains innovative micromechanical modeling techniques for a variety of material behaviors Examines how these models can be applied to metal forming processes in practice, including blanking, arrowed cracks in drawing, and surface cracks in upset forging Provides a thorough examination of both macroscopic and microscopic ductile fracture theory

Author: Michael A. Kaplan
Publisher:
ISBN:
Category : Alloys
Languages : en
Pages : 64

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Author: Ryan James Cooke
Publisher:
ISBN: 9781339542324
Category :
Languages : en
Pages :

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Book Description
The micro-mechanics based approach to the study of ductile fracture has successfully overcome many of the limitations (such as large scale material yielding, cyclic loading, and size/scale dependence of J) of traditional fracture mechanics approaches (i.e. K, J and CTOD's). A number of the currently available micro-mechanics models (i.e. SMCS, Hancock and McKenzie, 1975; VGM, Kanvinde and Deierlein, 2006) predict fracture accurately under high triaxiality and axisymmetric conditions; however, the mentioned conditions do not encompass the full range of stress states (including low-triaxiality or non-axisymmetric conditions) which are relevant to the structural, mechanical and aerospace industries. As such, the primary objective of the work presented in this dissertation is to inform the development of a more general damage model which is applicable to a broader range of stress states and seismic (i.e. cyclic) loading which can result in ultra-low cycle fatigue (ULCF) failures. New model development is realized through a collaborative multi-scale approach which combines the results of an extensive test series (Smith, 2014) and a series of computational void simulations. To probe the full range of practical stress/loading conditions, a more general finite element (FE) framework for simulating the response of micro-voids is developed. The new void cell framework and the results of the 146 void simulations comprise the primary body of work presented in this dissertation. The void simulations can be divided into two groups: (1) those which effectively simulate an array of voids while modeling a representative void cell, and (2) those which explicitly model an array of voids. Void growth rates measured from the single void model (SVM) are used to inform the selection of a new functional form for the damage model presented in this dissertation while the multi-void model (MVM) provides qualitative and quantitative insights regarding localized deformation between neighboring voids. Findings from the MVM simulations are (1) in agreement with observations obtained from sectioned images (Smith, 2014) of fracture coupons that expose undergrown voids in the near vicinity of the failure surface and (2) are used to develop a strain-based indicator for localization initiation that shows strong agreement with failure strains observed from coupon scale tests (Myers, 2009). Moreover, the trends observed from both model types indicate that there is minimal void growth and that localization does not occur at low triaxialities. Both finding suggest that an alternate fracture mechanism than the traditionally excepted 'growth to coalescence' mechanism is active under these conditions. Despite the power of micro-mechanics based models, the ability to arrive at accurate fracture predictions is contingent on the calibration of the parameters which define the material constitutive response. The capability for complementary FE simulations to reproduce the force-displacement response obtained from physical tests (which is typically relied upon for model calibration) provides a false sense of security and neglects issues (i.e. non-uniqueness of the model parameter set) associated with model over-fitting. To investigate the susceptibility of typical calibration approaches to result in non-unique fits, a simple example is employed. Results of the example demonstrate that (1) multiple (and therefore non-unique) parameter sets may adequately reproduce the force-displacement response of typical calibration specimen and (2) that local plastic strains (often used to evaluate local fracture criteria) can result in error more than 65% despite agreement with the calibration metric. Thus, selection of parameter sets based solely on qualitative agreement between test data and complementary simulations can lead to erroneous results when evaluating material resistance to fracture.

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: Matthieu Dunand
Publisher:
ISBN:
Category :
Languages : en
Pages : 256

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Book Description
Accurate predictions of the onset of ductile fracture play an increasingly important role in the design of lightweight sheet metal structures. With the development of virtual prototyping practices, most transportation vehicles are now computer-engineered in great detail before launching their mass production, thereby requiring reliable models for plasticity and fracture. This thesis reports on a comprehensive investigation into the effect of stress state on the onset of ductile fracture of an Advanced High Strength Steel (AHSS), covering development of new experimental procedures, material characterization and phenomenological as well as micro-mechanical modeling of the onset of fracture. Based on an extensive multi-axial experimental program, the anisotropic plasticity of the present material is described by a non-associated quadratic anisotropic model. Comparison of model predictions to experimental results reveals that the proposed model provides better predictions than associated isotropic or anisotropic quadratic models. Moreover, a structural validation is presented that demonstrates the higher prediction accuracy of the non-associated plasticity model. A hybrid experimental-numerical approach is proposed to investigate the dependence of the onset of fracture to stress state. The experimental program covers the complete range of positive stress triaxialities, from pure shear to equibiaxial tension. It includes different full thickness specimens as well as multi-axial fracture experiments where combinations of tension and shear loadings are applied to a newly developed butterfly-shaped specimen. Loading paths to fracture are determined for each experiment in terms of stress triaxiality, Lode angle parameter and equivalent plastic strain and show a non-monotonic and strong dependence of ductility to stress state. The extensive fracture characterization is used to evaluate the predictive capabilities of two phenomenological and physics-inspired fracture models (the Modified Mohr-Coulomb and a shear-modified Gurson model) that take the effect of the first and third stress tensor invariants into account in predicting the onset of fracture. Finally, a micro-mechanical model relating the onset of fracture to plastic localization into a narrow band at the micro-scale is developed. The effect of stress state on localization is investigated numerically by means of a 3D void-containing unit cell submitted to well-controlled and proportional loadings in the macroscopic stress state. Based on simulation results, an analytical localization criterion is proposed which defines an open convex envelope in terms of the shear and normal stresses acting on the plane of localization and correlates well with experimental results.

Author: Chengyang Wang
Publisher:
ISBN:
Category : Metals
Languages : en
Pages : 244

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Author: Heng Li
Publisher: Elsevier
ISBN: 0128143827
Category : Technology & Engineering
Languages : en
Pages : 350

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Book Description
Deformation Based Processing of Materials: Behavior, Performance, Modeling and Control focuses on deformation based process behaviors and process performance in terms of the quality of the needed shape, geometries, and the requested properties of the deformed products. In addition, modelling and simulation is covered to create an in-depth and epistemological understanding of the process. Other topics discussed include ways to efficiently reduce or avoid defects and effectively improve the quality of deformed parts. The book is ideal as a technical document, but also serves as scientific literature for engineers, scientists, academics, research students and management professionals involved in deformation based materials processing. Covers process behaviors, such as non-uniform deformation, unstable deformation, material flow phenomena, and process performance Includes modelling and simulation of the entire deformation process Looks at control of the preferred deformation, undesirable material flow, avoidance and reduction of defects, and improving the dimensional accuracy, surface quality and microstructure construction of the produced products

Author: Xin Min Lai
Publisher: CRC Press
ISBN: 0429846983
Category : Science
Languages : en
Pages : 477

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Book Description
The book presents a compilation of research on meso/microforming processes, and offers systematic and holistic knowledge for the physical realization of developed processes. It discusses practical applications in fabrication of meso/microscale metallic sheet-metal parts via sheet-metal meso/microforming. In addition, the book provides extensive and informative illustrations, tables, case studies, photos and figures to convey knowledge of sheet-metal meso/microforming for fabrication of meso/microscale sheet-metal products in an illustrated manner. Key Features • Presents complete analysis and discussion of micro sheet metal forming processes • Guides reader across the mechanics, failures, prediction of failures and tooling and prospective applications • Discusses definitions of multi-scaled metal forming, sheet-metal meso/microforming and the challenges in such domains • Includes meso/micro-scaled sheet-metal parts design from a micro-manufacturability perspective, process determination, tooling design, product quality analysis, insurance and control • Covers industrial application and examples

Author: Bradley Dodd
Publisher: Academic Press
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 328

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