Integrated Multiscale Characterization and Modeling of Ductile Fracture in Heterogeneous Aluminum Alloys PDF Download

Author: Dakshina M. Valiveti
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 131

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Book Description
The multiscale model developed in this work captures detailed microscopic crack initiation and propagation in a large domain with minimal computational expense. The effectiveness of this multiscale characterization-modeling framework is demonstrated by studying structure-property relation and simulating ductile fracture in cast Aluminum alloy A319.

Author: Daniel Paquet
Publisher:
ISBN:
Category :
Languages : en
Pages : 215

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Book Description
Abstract: Cast aluminum alloys and discontinuously reinforced aluminums (DRAs) are widely used in automotive, aerospace, nuclear and other engineering systems due to their advantageous strength-to-density ratio. Their microstructure is characterized by a dispersion of hard and brittle heterogeneities in a softer aluminum matrix. These microstructural heterogeneities increase the strength of the alloys, but also affect their failure properties like fracture toughness and ductility in an adverse manner. Important micromechanical damage modes that are responsible for deterring the overall failure properties include inclusion cracking, followed by ductile matrix failure due to void initiation, growth and coalescence. The complex interaction between competing damage modes makes failure and ductility prediction for these materials quite challenging. Sensitivity studies performed in this work with the locally enhanced Voronoi cell finite element method (LE-VCFEM) show a strong influence of microstructure morphology on ductile failure of microstructural domains. Unfortunately, micromechanical analysis of microstructural regions at the scale of structural components are prohibitive due to the enormous number of heterogeneities in the underlying microstructure.

Author: Waqas Muhammad
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
Finite element (FE) simulations are widely used in automotive design processes to model the forming and crashworthiness behavior of structural materials. Comprehensive material characterization and the availability of suitable constitutive models are prerequisites for accurate modeling of these operations. Numerical modeling of formability and crashworthiness is complex as it involves large deformations, instability, ruptures, damage propagation, and fracture. The effectiveness of computer-aided engineering (CAE) based design and performance evaluations significantly depends on the ability of numerical models to predict the material work hardening behavior, flow localization and fracture. This thesis presents a combined experimental and numerical study to explore microstructure property relationships involving strain localization, shear banding and fracture in precipitation hardened aluminum alloys. More specifically, the AA6xxx series aluminum alloys are of key interest for automotive applications, requiring good formability, hemmability and crash energy absorption characteristics. The goal of this work is to enhance the existing experimental understanding and modeling capabilities with respect to strain localization, shear banding and fracture in AA6xxx series precipitation hardened aluminum alloys, through development and coupling of multiscale modeling frameworks with advanced constitutive models for material work hardening and failure. In these regards, a crystal plasticity based constitutive hardening model is developed to account for the intragranular backstresses that arise from the formation of deformation induced dislocation substructure in precipitation hardened aluminum alloys. Based on thorough experimental investigation, it is learned that the substructure starts as pinned dislocation tangles with some regions having relatively high dislocation content while others being virtually dislocation free. With persistent deformation the substructure evolves into a well defined equiaxed cell/subgrain structure with majority of dislocations being trapped at the subgrain cell wall boundaries. The substructure induces intragranular backstresses due to blockage of dislocation passage leading to the experimentally observed Bauschinger effect at the macroscopic scale. The proposed hardening model accounts for these induced stresses and successfully predicts the experimentally measured flow behavior during cyclic simple shear and cyclic TCT and CTC loadings of AA6063. More importantly, the new backstress hardening model successfully reproduces the experimentally observed Bauschinger effect upon loading reversal. It is further shown that the crystallographic texture evolves significantly during cyclic simple shear deformation and the model successfully predicts the experimentally observed texture evolution. The study reveals that for proper prediction of flow behavior and the experimentally observed Bauschinger effect in precipitation hardened aluminum alloys, a physically motivated model that can account for the induced internal stresses, must be employed to describe material hardening on a polycrystalline level. Next, a multiscale modeling approach is developed where a macro-scale component level simulation is performed using conventional phenomenological plasticity and the boundary conditions of the region of interest are extracted and applied to the crystal plasticity based finite element model to account for the relevant microstructural physics. The proposed approach is successfully validated by simulating wrap-bending deformation of AA6063 and by comparing the observed texture evolution, slip band formation within grains, through thickness strain localization and the development of surface roughness with corresponding experimental data. The proposed approach enhances existing modeling capabilities for better predictability of material response under complex loading paths. After developing the multiscale framework, a new constitutive approach is developed to predict failure by extending the existing nano-void theory of ductile failure to precipitation hardened aluminum alloys by accounting for the effects of precipitation induced dislocation substructure on point defect generation. A new evolution law for the effective obstacle strength associated with substructure evolution is incorporated into the formulation. The proposed failure criterion is successfully validated against experimental data and its versatility is demonstrated by coupling the failure criterion with stress-strain data generated through crystal plasticity simulations, to predict failure strain for arbitrary loading - stress triaxiality conditions. Next, a comprehensive experimental investigation is performed to study the relationship between microstructure, plastic deformation and fracture behavior of precipitation hardened aluminum alloy AA6016 during bending. It is shown that the bendability of AA6016 alloy is limited by the formation of severe surface undulations and surface cracking, which are associated with the heterogenous nature of slip concentrating into coarse slip bands and intense shear banding originating from surface low cusps in the form of mutually orthogonal transgranular bands. Micro-cracks originate from low cusp regions along the outer tensile surface and propagate along the intensely sheared planes within shear bands. Results show that grains with S texture component are prone to shear banding and failure during bending and the contrary is true for Cube oriented grains. It is observed that intergranular micro-void nucleation and crack propagation is favored in areas with high grain boundary misorientations and intense slip band impingements along boundaries, perhaps due to the reduction in local cohesive strength of such boundaries. Finally, the developed multiscale modeling approach in conjunction with the newly developed hardening and failure models for age-hardenable aluminum alloys are applied to predict the experimentally observed shear banding and fracture behavior of AA6016 during bending. The simulated results successfully predict the experimentally observed shear banding and the predominant transgranular fracture behavior. It is shown that the advancing crack tip alternates from a less critical localization condition to a more critical one, as it requires lesser energy for the creation of new fracture surfaces while still sustaining the imposed plastic deformation. It is observed that Copper, Brass and Cube texture components show good resistance to shear banding and are therefore characterized as high bendability components, whereas the contrary is true for the S texture component. Lastly, the coupled numerical framework, presented herein, provides an excellent tool for CAE, virtual material characterization and analysis of microstructure-property relationships.

Author: Chao Hu
Publisher:
ISBN:
Category : Aluminum alloys
Languages : en
Pages : 137

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Book Description
Abstract: Ductile heterogeneous materials like cast aluminum alloys, undergo catastrophic ductile failure that initiates with particle fragmentation with evolves with void growth and coalescence in localized bands of intense plastic deformation and strain softening. Conventional Voronoi Cell finite element model (VCFEM), based on the assumed stress hybrid formulation, is for small deformation and is unable to account for plastic strain induced softening. To overcome this shortcoming of material softening due to plastic strain localization, this work introduces a locally enhanced Voronoi Cell finite element model (LE-VCFEM) for modeling the very complex phenomenon of ductile failure in heterogeneous metals and alloys. In LE-VCFEM, finite deformation displacement elements are adaptively added to regions of localization in the otherwise assumed stress based hybrid Voronoi cell finite element to locally enhance modeling capabilities for ductile fracture. Adaptive h-refinement is used for the displacement elements to improve accuracy. Damage initiation by particle cracking is triggerred by a Weibull model. The nonlocal Gurson-Tvergaard-Needleman model of porous plasticity is implemented in LE-VCFEM to model matrix cracking. An iterative strain update algorithm is used for the displacement elements. The LE-VCFEM code is validated by comparing with results in the literature and with conventional FE codes. Furthermore, LE-VCFEM simulations of real microstructures are satisfactorily conducted, establishing the high potential of this method.

Author: Meng Luo (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 311

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Book Description
Anisotropic mechanical properties are common in plastically deformed or thermomechanically processed metallic materials, e.g. in rolled or extruded sheet. Among them, the anisotropy of large strain plastic deformation and ductile fracture under multi-axial loading is highly relevant to various industrial applications such as metal forming, impact failure of structures, etc. In this thesis, a comprehensive study of the plasticity and ductile fracture of anisotropic metal sheets is presented, covering experimental characterization, constitutive modeling and numerical implementation. On the basis of an extensive multiaxial experimental program, the anisotropic plasticity of the present aluminum alloy is modeled using a macroscopic phenomenological model and a polycrystalline plasticity model, respectively. The proposed phenomenological modeling makes use of a linear-transformation- based orthotropic yield function with pressure dependence, as well as a combined isotropic/kinematic hardening law, and is able to capture most features of the anisotropic plastic behavior under various multi-axial stress states with good accuracy and computational efficiency. At the same time, a physically-motivated self-consistent polycrystalline plasticity model is utilized to describe the texture-induced anisotropy and through-thickness heterogeneity of the present sheet material. A Reduced Texture Methodology (RTM) is developed to provide the computational efficiency needed for industrial applications. In additional to an accurate prediction of all macroscopic material behaviors, the polycrystalline model reveals that the development of the crystallographic texture is the underlying mechanism of plastic anisotropy and heterogeneity. The anisotropic ductile fracture of the present aluminum alloy extrusion is investigated using a hybrid experimental-numerical approach. The experimental results show a strong dependency of the strain to fracture on the material orientation with respect to the loading direction. A new non-associated anisotropic fracture model is proposed which makes use of a stress state dependent fracture locus and an anisotropic plastic strain measure obtained through the linear transformation of the plastic strain tensor. It is shown that the use of the Modified Mohr-Coulomb (MMC) stress state weighting function in this anisotropic fracture modeling framework provides accurate predictions of the onset of fracture for all fourteen distinct fracture experiments. The proposed plasticity and fracture modeling framework is successfully validated on a industrial stretch-bending operation.

Author: Somnath Ghosh
Publisher: Springer Science & Business Media
ISBN: 1441906436
Category : Science
Languages : en
Pages : 669

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Book Description
Computational Methods for Microstructure-Property Relationships introduces state-of-the-art advances in computational modeling approaches for materials structure-property relations. Written with an approach that recognizes the necessity of the engineering computational mechanics framework, this volume provides balanced treatment of heterogeneous materials structures within the microstructural and component scales. Encompassing both computational mechanics and computational materials science disciplines, this volume offers an analysis of the current techniques and selected topics important to industry researchers, such as deformation, creep and fatigue of primarily metallic materials. Researchers, engineers and professionals involved with predicting performance and failure of materials will find Computational Methods for Microstructure-Property Relationships a valuable reference.

Author: Jun Zhou
Publisher:
ISBN:
Category : Alloys
Languages : en
Pages : 149

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Book Description
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.

Author: Jerzy Leszczynski
Publisher: Springer Science & Business Media
ISBN: 9048126878
Category : Science
Languages : en
Pages : 468

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Book Description
"Practical Aspects of Computational Chemistry" presents contributions on a range of aspects of Computational Chemistry applied to a variety of research fields. The chapters focus on recent theoretical developments which have been used to investigate structures and properties of large systems with minimal computational resources. Studies include those in the gas phase, various solvents, various aspects of computational multiscale modeling, Monte Carlo simulations, chirality, the multiple minima problem for protein folding, the nature of binding in different species and dihydrogen bonds, carbon nanotubes and hydrogen storage, adsorption and decomposition of organophosphorus compounds, X-ray crystallography, proton transfer, structure-activity relationships, a description of the REACH programs of the European Union for chemical regulatory purposes, reactions of nucleic acid bases with endogenous and exogenous reactive oxygen species and different aspects of nucleic acid bases, base pairs and base tetrads.

Author: Franz Roters
Publisher: John Wiley & Sons
ISBN: 3527642099
Category : Technology & Engineering
Languages : en
Pages : 188

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Book Description
Written by the leading experts in computational materials science, this handy reference concisely reviews the most important aspects of plasticity modeling: constitutive laws, phase transformations, texture methods, continuum approaches and damage mechanisms. As a result, it provides the knowledge needed to avoid failures in critical systems udner mechanical load. With its various application examples to micro- and macrostructure mechanics, this is an invaluable resource for mechanical engineers as well as for researchers wanting to improve on this method and extend its outreach.

Author: Olaf Engler
Publisher: CRC Press
ISBN: 1420063669
Category : Science
Languages : en
Pages : 490

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Book Description
The first edition of Introduction to Texture Analysis: Macrotexture, Microtexture, and Orientation Mapping broke new ground by collating seventy years worth of research in a convenient single-source format. Reflecting emerging methods and the evolution of the field, the second edition continues to provide comprehensive coverage of the concepts, pra