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 Development of Numerical Approaches to Predict Ductile and Cleavage Fracture of Structural Materials written by Guihua Zhang and published by . This book was released on 2007 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Numerical simulations mainly using finite element method are playing a more and more important role in prediction of fracture-induced failure for high performance structure. This thesis seeks to develop numerical approaches to predict ductile and cleavage fracture in structural materials. For ductile fracture, the discrete void approach reveals the failure mechanisms explicitly and is used to study the trends of fracture toughness. The porous continuum approach provides an effective means to predict extensive crack propagation. We consider the occurrence of material failure (void coalescence) as when localization of plastic flow takes place in the inter-void ligament and obtain the failure criterion as a function of the stress triaxiality ratio and the Lode angle. The Gologanu-Leblond Devaux (GLD) model, which accounts for the evolution of both void volume and void shape, is used to describe the porous placticity behavior and is implemented into ABAQUS via a user subroutine. Numerical simulations are performed to predict extensive crack growth in ductile solids for a thin aluminum 2024-T3 plate and verified by successful predication of crack extension in various specimens, including the multiple site damage speciments. The effect of stress triaxiality and Lode angle is further analyzed and the Xue-Wierzbicki fracture locus is employed as a criterion for void colescence. Combination of GLD model and X-W fracture locus is then applied to a DH-36 steel with specimens experiencing a wide range of stress triaxiality and Lode angles at failure. The numerical simulation results agree very well with the experimental results. For cleavage fracture, a modified three parameter Weibull stress model is proposed and used to predict the fracture of A508 steel at three different temperatures. By integrating the Weibull stress model over the plastic process zone, the failure probability can be obtained and comparison is made with the experiment result. Issues addressed include calibration of the model parameters, introduction of a threshold parameter, dependencies of the model parameters on temperature, plastic strain effect and crack tip triaxiality effect, etc."--Abstract.

Download or read book Numerical Modeling of Ductile Fracture written by Jun Zhou and published by . This book was released on 2013 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis sought to investigate and develop valid numerical approaches to predict ductile fracture under different stress state and loading conditions. As the first portion of this work, the plastic flow and fracture behaviors of three aluminum alloys (5083-H116, 6082-T6 and 5183 weld metal) under the effects of strain rate and temperature were studied through a series of experiments and finite element analyses. The fracture behavior under the influential factor of stress triaxiality was also studied. The applicability of the Johnson-Cook plasticity and fracture models were investigated with mixed results. For all three materials, the dependency of the failure strain on triaxiality is adequately described. The stress state effect on plasticity and ductile fracture behaviors was further explored for aluminum alloy 5083-H116 through tests on plane strain specimens and torsion specimens, focusing on the third deviatoric stress invariant (lode angle). A stress state dependent plasticity model, J2-J3 model, together with the Xue-Wierzbicki fracture criterion which defined the damage parameter as a function of the stress triaxiality and the Lode angle, was implemented and calibrated with the test data. The calibrated model was utilized to study the residual stress effect on ductile fracture resistance, using compact tension specimens with residual stress fields generated from a local out-of-plane compression approach. Fracture tests with positive and negative residual stresses were conducted on the C(T) specimens. Both experimental and finite element results showed significant effect of residual stress on ductile fracture resistance. In an attempt to predict ductile fracture under shear-dominated conditions, this study combined the damage mechanics concept with the Gurson-Tvergaard-Needleman porous plasticity model that accounts for void nucleation, growth and coalescence. The GTN model was extended by coupling two damage parameters, representing volumetric damage and shear damage respectively, into the yield function and flow potential. The new model was validated through a series of numerical tests in comparison with existing GTN type models, and applied to predict the ductile fracture behaviors of a beta-treated Zircaloy-4. With model parameters calibrated using experimental data, the model was able to predict failure initiation and propagation in various specimens experiencing a wide range of stress states.

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 294 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 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 A Study of Ductile Fracture Prediction in Microforming Process written by Jiaqi Ran and published by . This book was released on 2014 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 and Ductility written by Bradley Dodd and published by Academic Press. This book was released on 1987 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Investigation of Stress and Strain Parameters in the Prediction of Ductile Fracture written by Michael A. Kaplan and published by . This book was released on 1976 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effects of Finite Element Mesh on Numerical Prediction of Ductile Tearing written by B. Skallerud and published by . This book was released on 1999 with total page 14 pages. Available in PDF, EPUB and Kindle. Book excerpt: Presently, there is still no generally accepted way of calibrating material models accounting for ductile damage, and calibrating the finite element model with this material in order to obtain a representative length scale via the smallest element size. Roughly, one may identify two approaches. One is based on computational cells, where the cells accounting for damage growth are put in a layer in the prospective crack growth direction. The cell size, D, and initial void volume fraction,f0, are argued to be microstructurally based. The simulations are calibrated against a fracture test. The second approach is to a larger extent based on metallurgical observations, and is more in accordance with the objective that the material model is calibrated with simple test specimens (smooth tensile specimens). But also with this method the finite element mesh has to be calibrated against a fracture test. Hence, the finally chosen element size introduces the required length scale. The present study corresponds to the second approach. It focuses on one set of material parameters established in an earlier study. The material is a typical structural steel in the medium strength range. Results from a purely numerical study are presented for a plane strain three point bend specimen. Effects of finite element type, mesh size, mesh irregularity, and damage material layers are considered. These results illustrate the effects of mesh on ductile tearing prediction. Then 3D analyses of a 3PB test are carried out in order to compare a calibrated element size against the sizes applied in the plane strain study.

Download or read book Prediction of Ductile Fracture of Thin Walled Cylinders Subjected to Localized Intense Heat written by and published by . This book was released on 2004 with total page 77 pages. Available in PDF, EPUB and Kindle. Book excerpt: The objective of this research was to further develop two models that are capable of predicting crack growth in ductile materials. In this study, we measured CTOA (crack tip opening angle) at elevated temperatures for a stainless steel and aluminum alloy 2014-T6. The CTOA curves were then used as the fracture criterion to simulate crack extension and instability in thin-walled cylinders subjected to localized intense heat. The commercial finite element code ABAQUS was used in conjunction with a user subroutine to implement the CTOA fracture criterion to perform the simulation. The result of the numerical simulations indicated that the effect of temperature on the level of burst pressure of the cylinder is not very significant. One explanation for this interesting behavior is that the heated zone that contains the crack would be subject to compressive stresses because of a greater thermal expansion. In this study, an analytical damage length (DL) model has been further developed to account for the thermal effect in addition to the large deflection effect. The DL model was also used to predict the burst pressure of steel and aluminum cylinders and the results are compared favorably with those predicted by the CTOA approach.

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 Numerical model studies on ductile fracture written by Minoru Taya and published by . This book was released on 1977 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Peridynamic Modeling of Large Deformation and Ductile Fracture written by Masoud Behzadinasab and published by . This book was released on 2019 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: Prediction of ductile fracture, which is a prevalent failure mode in most engineering structures, is vital to numerous industries. Despite significant advancements in fracture mechanics, ductile fracture modeling has remained a challenging task and a continuing area of research. The peridynamic theory has attracted broad interest in recent years, for its innovative approach for simulating material damage. While peridynamics has been largely utilized to simulate cracking events in brittle materials, its ability in predicting ductile failure remains mostly untested. In this dissertation, a rigorous investigation into the capabilities of peridynamics in simulating ductile fracture in metallic alloys is undertaken. The third Sandia Fracture Challenge, as a true blind prediction challenge, is employed in this examination. In this challenge, the state of the art of the peridynamic modeling of ductile fracture is implemented to predict deformations and failure of an additively manufactured metal, with a complex geometry, under the dynamic tensile experiments performed by Sandia National Laboratories. Following the participation in the challenge, while our modeling approach led to qualitatively good blind predictions and a correctly predicted crack path, it underpredicted the load-carrying capacity of the structure and simulated an early fracture. Our post-experiment analysis identifies the main sources of discrepancy between the blind simulations and experiments to be (1) material instabilities associated with the finite deformation peridynamic model and (2) unreliability of a Lagrangian peridynamic framework in solving problems involving extremely large deformation and extensive damage. To address the aforementioned issues, a novel bond-associated, semi-Lagrangian, constitutive correspondence, peridynamic framework is proposed, in which peridynamic material point interactions depend only on their current properties (e.g. position and stress values) in the deformed configuration, and a rate-based approach is utilized to advance the state of material. A nonlocal version of the velocity gradient is presented to determine the Cauchy stress rate, using local constitutive theories, as an intermediate quantity in computing peridynamic bond forces. A novel bond-associated, correspondence damage modeling is introduced by using the bond-associated internal properties, e.g. stress and strain values, to incorporate classical failure criteria within the peridynamic framework. The new theory is employed to revisit the Sandia Fracture Challenge problem. Our results indicate that the new approach significantly improves the peridynamic predictions of large deformation and ductile fracture

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 Applied Mechanics Reviews written by and published by . This book was released on 1965 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1975 with total page 1004 pages. Available in PDF, EPUB and Kindle. Book excerpt: