Download or read book Experimental and numerical investigation of ductile fracture initiation at low intermediate and high strain rates written by Christian C.. Roth and published by . This book was released on 2015 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cette thèse porte sur l'effet du taux de déformation sur l'initiation de la rupture ductile des métaux dans les aciers avancés à haute résistance (AHSS). Une analyse détaillée de la plasticité des AHSS (effet de la température et au taux de déformation) est requise, ainsi que la caractérisation de l'effet de l'état des contraintes. Les principaux résultats de cette thèse sont : (i) des essais novateurs pour déterminer la déformation à rupture dans les toles sous chargement proportionnel pour des chargements allant du cisaillement pur à la traction équi-biaxiale (ii) le développement d'une technique expérimentale permettant de réaliser des essais à rupture sur toles avec des barres de Hopkinson (SPHB) (iii)) un modèle de plasticité en grandes déformations incluant la dépendance au taux de déformation et à la température (iv) un modèle d'initiation de la rupture ductile dépendant du taux de déformation et (v) des observations micrographiques montrant une augmentation significative de la localisation de déformation à de forts taux de déformation. Outre une introduction générale, des conclusions, et un chapitre de perspectives, la thèse comprend quatre chapitres principaux: Dans le premier chapitre, un programme basique d'essais à rupture pour les toles est développé afin de caractériser l'amorce de la rupture ductile sous différents états de contraintes. Une éprouvette plane comportant deux sections utiles paralèlles est proposée pour déterminer la déformation à rupture pour des états de contraintes proches du cisaillement pur. Une méthodologie basée sur des simulations EF est développée pour optimiser la géométrie de l'éprouvette en fonction de la ductilité du matériau et de son écrouissage. Une éprouvette de traction trouée est optimisée pour déterminer la ductilité en traction uniaxiale. La déformation plane est étudiée par flexion d'une large bande, tandis qu'un essai de poinçonnement miniature est utilisé pour la traction equi-biaxiale. Dans un deuxième chapitre, un système d'inversion est développé pour des essais de traction à de forts taux de déformations avec des SPHB. Une barre de sortie située au-dessus de la barre d'entrée permet de mesurer l'effort de traction, tandis que le déplacement de l'éprouvette est mesuré par caméra rapide. Cette configuration permet une durée d'essais deux fois plus long qu'un système conventionnel de Kolsky, et des essais à des taux intermédiaires (~100/s) sans augmenter la longueur totale du système. Dans un troisième chapitre, des essais de traction à divers taux de déformation sont réalisés sur des éprouvettes plates lisses, entaillées et trouées. La rupture est précédée d'une striction. Une approche hybride expérimentale et numérique est utilisée pour calculer la déformation à rupture. Une dépendance au taux de déformation et à la température de type Johnson-Cook avec un écrouissage combiné Swift-Voce est utilisée avec une loi d'écoulement anisotrope non-associée pour décrire précisément les champs locaux de déformation. Les variations de tempréatures ne sont pas calculées en résolvant le problème thermo-mécanique complet, mais au moyen d'une fonction de poids dépendant du taux de déformation. Ces résultats sont ensuite utilisés pour calibrer et valider une extension récente du modèle d'initiation de rupture d'Hosford-Coulomb, prenant en compte l'effet du taux de déformation. Dans un quatrième chapitre, des essais sur éprouvettes de cisaillement sont réalisés pour une large gamme de température et de taux de déformation. La déformation de l'éprouvette est soigneusement analysée par corrélation d'images numériques et par une approche hybride expérimentale et numérique. Des analyses EBSD sont réalisées sous la surface de rupture, mettant en évidence l'influence de la vitesse de chargement sur la déformation de la microstructure.

Download or read book Ductile Fracture After Complex Loading Histories written by Stephane Jean Marie Marcadet and published by . This book was released on 2015 with total page 173 pages. Available in PDF, EPUB and Kindle. Book excerpt: In engineering practice, sheet metal often fails after complex strain paths that deviate substantially from the widely studied proportional loading paths. Different from previous works on the ductile fracture of sheet metal, this thesis research addresses the experimental and modeling issues related to the crack initiation in advanced high strength steels after loading direction reversal. The main outcome of the present work is a fracture initiation model for proportional and non-proportional loading. The starting point of this thesis is a first chapter on the development of a micromechanically-motivated ductile fracture initiation model for metals for proportional loading. Its formulation is based on the assumption that the onset of fracture is imminent with the formation of a primary or secondary band of localization. Motivated by the results from a thorough unit cell analysis, it is assumed that fracture initiates after proportional loading if the linear combination of the Hosford equivalent stress and the normal stress acting on the plane of maximum shear reaches a critical value. A comprehensive fracture initiation model is then obtained after transforming the localization criterion from the stress space to the space of equivalent plastic strain, stress triaxiality and Lode angle parameter using the material's isotropic hardening law. Experimental results are presented for three different advanced high strength steels. For each material, the onset of fracture is characterized for five distinct stress states, including butterfly shear, notched tension, tension with a central hole, and punch experiments. The comparison of model predictions with the experimental results demonstrates that the proposed Hosford-Coulomb model can predict with satisfactory accuracy the instant of ductile fracture initiation in advanced high strength steels. In a subsequent chapter, experimental methods are developed to perform compression tension experiments. In addition, a finite strain constitutive model is proposed combining a Swift-Voce isotropic hardening law with two Frederick-Armstrong kinematic hardening rules and a Yoshida-Uemori type of hardening stagnation approach. The plasticity model parameters are identified from uniaxial tension-compression stress-strain curve measurements and finite element simulations of compression-tension experiments on notched specimens. The model predictions are validated through comparison with experimentally-measured load-displacement curves up to the onset of fracture, local surface strain measurements and longitudinal thickness profiles. The extracted loading paths to fracture show a significant increase in ductility as a function of the compressive pre-strain. The Hosford-Coulomb model is therefore integrated into a non-linear damage indicator modeling framework to provide a phenomenological description of the experimental results for monotonic and reverse loading. Another extension of the modeling framework is presented in a third chapter inspired by the results from loss of ellipticity analysis. It is demonstrated that the Hosford-Coulomb model can also be expressed in terms of a stress-state dependent critical hardening rate. Moreover, it is shown that the critical hardening rate approach provides accurate predictions of the instant of fracture initiation for both proportional and non-proportional loading conditions. Enhancements of the finite strain constitutive model are also proposed to enable a fast identification of all model parameters. The plasticity model parameters are identified from stress-strain curve measurements from shear loading reversal on specimens with a uniform thickness reduced gage section. The model is used to estimate the local strain and stress fields in fracture experiments after shear reversal. The extracted loading paths to fracture show a significant increase in ductility as a function of the strain at shear reversal, a feature that is readily predicted by the prosed critical hardening rate model.

Download or read book Experimental and Numerical Analysis of Ductile Fracture Under Multiaxial Loading written by Jessica Papasidero and published by . This book was released on 2014 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Experimental and Numerical Investigation of Formability and Ductile Fracture in Incremental Sheet Forming written by Shakir Madhloom Gatea and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Numerical Prediction of Ductile Fracture Due to Moving Load written by Md Abdullah and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This study investigates the effect of moving load on ductile fracture of shipbuilding metals through numerical simulation. Quinton [1,2] and Alsos [3] investigated moving load's effect on metals, in the plastic regime, and found that moving load results in a significant reduction in plastic capacity of metals. This study complements their work by extending the scope of the work up to ductile fracture initiation which was accomplished by implementing state-of-art ductile fracture model in moving loading scenario. A state-of-art ductile fracture model has been implemented in this study by incorporating the knowledge acquired by research in the fracture mechanics arena. A stress state based fracture locus with strain rate and temperature effects has been selected as the ductile fracture criteria accordingly. Finite Element Method with Explicit Time Integration scheme deemed appropriate for numerical simulation and LS-DYNA has been chosen to accomplish this consequently. This study attempts to mitigate two significant limitations of maritime structural assessment techniques associated with ship-ice interaction; undue simplification of load definition and over conservatism on fracture strain selection. Ship-ice interaction is considered as stationary loading scenario while it should be categorised as moving loading condition in accidental overloading situations. In addition, these techniques also regard fracture strain to be constant and independent of stress state, whereas studies show that ductile fracture initiation is highly dependent on the stress state. This study provides a method to incorporate stress-state dependent state-of-art ductile fracture model for numerical investigation of moving load.

Download or read book Studies on Strain Localization Ductile Fracture and Damage in Structural Metals written by Yazhi Zhu and published by . This book was released on 2017 with total page 666 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Ductile Fracture at Intermediate Stress Triaxialities written by Matthieu Dunand and published by . This book was released on 2013 with total page 256 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Experimental and Numerical Studies of Metal Deformation and Fracture at High Strain Rates written by G. H. Majzoobi and published by . This book was released on 1990 with total page 576 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Deformation and Fracture in Materials written by Anoop Kumar Mukhopadhyay and published by CRC Press. This book was released on 2024-08-27 with total page 373 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides information on the basics of deformation and fracture in materials and on current, state-of-the-art experimental and numerical/theoretical methods, including data-driven approaches in the deformation and fracture study of materials. The blend of experimental test methods and numerical techniques to study deformation and fracture in materials is discussed. In addition, the application of data-driven approaches in predicting material performance in different types of loading and loading environments is illustrated. Features: Includes clear insights on deformation and fracture in materials, with clear explanations of mechanics and defects relating to them Provides effective treatments of modern numerical simulation methods Explores applications of data-driven approaches such as artificial intelligence, machine learning, and computer vision Reviews simple and basic experimental techniques to understand the concepts of deformation and fracture in materials Details modeling and simulation strategies of mechanics of materials at different scales This book is aimed at researchers and graduate students in fracture mechanics, finite element methods, and materials science.

Download or read book Ductile Fracture in Metal Forming written by Kazutake Komori and published by Academic Press. This book was released on 2019-10-11 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

Download or read book Fracture Mechanics written by Satya N. Atluri and published by ASTM International. This book was released on 1992 with total page 448 pages. Available in PDF, EPUB and Kindle. Book excerpt: Papers of the June 1990 meeting held in Atlanta, Ga. The first volume (47 papers) concentrates on experimental and theoretical aspects of fracture mechanics. Volume two (26 papers) covers numerical and computational approaches. Topics include: ductile fracture, high-temperature and time-dependent fr

Download or read book NUMISHEET 2022 written by Kaan Inal and published by Springer Nature. This book was released on 2022-06-30 with total page 941 pages. Available in PDF, EPUB and Kindle. Book excerpt: The NUMISHEET conference series is the most significant international conference on the area of the numerical simulation of sheet metal forming processes. It gathers the most prominent experts in numerical methods in sheet forming processes and is an outstanding forum for the exchange of ideas and for the discussion of technologies related to sheet metal forming processes. Topics covered in this volume include but are not limited to the following: Materials Modeling and Experimental Testing Methods Friction and Contact Formability, Necking, and Fracture Instabilities and Surface Defects Fracture and Damage Numerical Methods Springback Incremental Sheet Forming Roll Forming Innovative Forming Methods Product and Process Design and Optimization

Download or read book Investigations Into Ductile Fracture and Deformation of Metals Under Combined Quasi static Loading and Under Extremely High rate Compressive Impact Loading written by Nathan Spulak and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Materials experiencing impact loading deform under complex three dimensional states of stress and at high strain rates. Accurately simulating impact events using finite element modeling requires material models capable of depicting the material behavior under these same conditions. In order to create accurate material models, this material behavior must first be determined experimentally. It is of particular interest to determine the equivalent plastic fracture strain at stress states consisting of in-plane biaxial tension and out-of-plane compression, and the plastic stress-strain response at strain rates on the order of 104 s-1. Both of these conditions are found during impact loading, and are outside the scope of current testing techniques. A new test technique is used to investigate Aluminum 2024, Titanium 6Al-4V, and Inconel 718 under in-plane biaxial tension and out-of-plane compression. The test consists of a small spherical or elliptical punch that is advanced into a thin specimen plate to induce in-plane biaxial tension on the back surface of the specimen. A second plate of an appropriate material is placed against the back surface of the specimen plate during loading in order to create out-of-plane compression. The equivalent plastic fracture strain at these stress states is determined from the experimental data and simulations using the commercial finite element software LS-DYNA. The same materials mentioned above are also tested using a modified, direct impact split-Hopkinson bar testing technique to induce strain rates greater than 104 s-1. For these tests, a small cylindrical specimen is placed in contact with the end of a larger cylindrical bar. The specimen is then impacted with a free flying cylindrical projectile to compress the specimen at a high rate of deformation. The stress-strain response of the material at these high strain rates is then investigated from the experimental data and in conjunction with LS-DYNA finite element simulations.

Download or read book Experimental and Numerical Study on the Effect of Strain Rate to Ductile Damage written by Andrew Scott Bowden and published by . This book was released on 2009 with total page 264 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Fracture Mechanics written by Walter G. Reuter and published by ASTM International. This book was released on 1995 with total page 842 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Formability of Metallic Materials written by D. Banabic and published by Springer Science & Business Media. This book was released on 2013-04-17 with total page 345 pages. Available in PDF, EPUB and Kindle. Book excerpt: After a brief introduction into crystal plasticity,the fun- damentals of crystallographic textures and plastic anisotro- py, a main topic of this book, are outlined. A large chapter is devoted to formability testing both for bulk metal and sheet metal forming. For the first time testing methods for plastic anisotropy of round bars and tubes are included. A profound survey is given of literature about yield criteria for anisotropic materials up to most recent developments and the calculation of forming limits of anisotropic sheet me- tal. Other chapters are concerned with properties of workpieces after metal forming as well as the fundamentals of the theory of plasticity and finite element simulation of metal forming processes. The book is completed by a collection of tables of international standards for formability testing and of flow curves of metals which are most commonly used in metal forming. It is addressed both to university and industrial readers.

Download or read book Experimental and Numerical Validation of a Ductile Fracture Local Criterion Based on a Simulation of Cavity Growth written by J-C Devaux and published by . This book was released on 1988 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt: A local criterion based on the simulation of hole growth by plastic deformation has been evaluated. Fracture of a material volume is reached for an assumed critical value of cavity growth. This critical value is determined from notched tensile tests. When dealing with cracked geometries, a process zone is introduced at the crack tip. This zone is modeled as the first mesh element (a)c at the crack tip in a finite-element code. The size of this element, which is a material constant, is measured from a conventional compact tension (CT) test. Different tests with cracked geometries were carried out on side-grooved CT specimens of different sizes (25 and 50-mm width) and on axisymmetrically cracked tensile bars (TA) with 15, 30, and 50-mm outer diameters. In all cases the fracture was flat with no shear lips. Keeping the parameters of the fracture local criterion constant, crack initiation and crack propagation were modeled using the node release technique. The numerical procedure and results are described in detail. The model results are shown to be in good agreement with the experimental results.