The Center for Predictive Integrated Structural Materials Science (PRISMS Center) is creating a u... more The Center for Predictive Integrated Structural Materials Science (PRISMS Center) is creating a unique framework for accelerated predictive materials science and rapid insertion of the latest scientific knowledge into next-generation ICME tools. There are three key elements of this framework. The first is a suite of high-performance, open-source integrated multi-scale computational tools for predicting microstructural evolution and mechanical behavior of structural metals. Specific modules include statistical mechanics, phase field, crystal plasticity simulation and real-space DFT codes. The second is the Materials Commons, a collaboration platform and information repository for the materials community. The third element of the PRISMS framework is a set of integrated scientific ''Use Cases'' in which these computational methods are linked with experiments to demonstrate the ability for improving our predictive understanding of magnesium alloys, in particular, the influence of microstructure on monotonic and cyclic mechanical behavior. This paper reviews progress toward these goals and future plans.
The critical energy release rate, defined as G c = 2γ+γ p (where γ is the cohesive energy and γ p... more The critical energy release rate, defined as G c = 2γ+γ p (where γ is the cohesive energy and γ p is the plastic work), is widely used as a macroscopic fracture criterion. During embrittlement of aluminum by gallium, impurity segregation is localized to a small region along the grain boundary and the bulk plastic properties are unaffected. Yet, the critical energy release rate (which is predominantly described by the plastic work [γ p ] since γ p > > γ) significantly decreases. In this work, we recognize that as the cohesive energy (γ) decreases during corrosion due to an increase in impurity concentration, the stress needed at the notch tip to form the crack decreases, and this, in turn, decreases the plastic work by reducing dislocation emission at the notch tip. We study two different models proposed in the past that can capture this dependence of γ p on γ during liquid metal (Ga) embrittlement of aluminum alloy (Al 7075). The parameters in these models are computed from first principles atomistic calculations and recent experiments. We compare and contrast these models on their ability to describe various aspects of embrittlement such as fracture toughness, K IC , and subcritical value of stress intensity, K Iscc. Extension of the approach to predict threshold fatigue crack initiation in Al7075 is suggested.
Lightweight materials such as Aluminum are prevalent in aerospace and automotive vehicles, but th... more Lightweight materials such as Aluminum are prevalent in aerospace and automotive vehicles, but the use of lighter Magnesium alloys will significantly increase fuel efficiency and cut emissions. Magnesium alloys present a wide array of unsolved scientific challenges, such as the deformation response of the slip and twin systems and the influence of dislocation interactions and twinning on tensile and fatigue behavior. In this thesis, a parallel three-dimensional(3D) crystal plasticity finite element opensource code was developed based on the deal.II finite element framework as part of PRISMS-Plasticity. Rate-independent crystal plasticity was implemented by developing a nonlinear algorithm which enables all the slip systems to lie on or inside the yield surface, and a consistent tangent modulus ensures convergence for small loading increments. A twin activation mechanism was incorporated into the framework based on a quadrature point sensitive scheme. Furthermore, by bounding the L-n...
Abstract The present work addressed the effects of heat treatment on the mechanical response of a... more Abstract The present work addressed the effects of heat treatment on the mechanical response of a WE43 Mg alloy using an integrated framework of SEM-DIC experiment and CPFE simulation. Both macroscopic responses including yield strength, ultimate strength, ductility, and microscopic responses, including local displacement and strain maps, were experimentally investigated. The focus of this work is to use the CPFE simulation as an integrated computational tool to study the effects of heat treatment. The CPFE framework was evaluated using the local fields of displacement and strain obtained from the SEM-DIC experiment rather than the conventional scheme of using macroscopic responses at different loading directions. Subsequently, the information which is available using CPFE, such as the critical resolved shear stress (CRSS) and relative slip activity, was used to study the effects of heat treatment on the response of WE43 Mg alloy. The contributions of different strengthening mechanisms on the CRSS were addressed. The results show that effects of heat treatment can be captured using the predominant mechanisms of the grain size effect and the influence of precipitates. Finally, it has been shown that classical Hall-Petch in which one constant can capture the size effects, should be modified. To do so, each deformation mode should have a unique Hall-Petch constant, which are calculated here for the WE43 Mg alloy.
The effect of aging on the accumulation of microscale plasticity, and the resulting macroscopic m... more The effect of aging on the accumulation of microscale plasticity, and the resulting macroscopic mechanical behavior, were examined in the magnesium alloy WE43 under uniaxial tension. Full-field strains on the length scale of the microstructure, and their relation to the underlying crystallography, were captured using a combination of electron backscatter diffraction, custom nanoparticle patterning processes for corrosion-susceptible alloys, scanning electron microscopy (SEM), in-SEM uniaxial tensile and compressive loading, and distortion-corrected digital image correlation. The as-received material exhibited an average grain size of 12 μm. The strain incurred on individual slip traces in magnesium was resolved for the first time. Insights into slip activation across the microstructure revealed that using Schmid's Law with the nominal Schmid Factor appeared to be predictive for basal and non-basal slip. The DIC results were compared with simulation using an advanced open-source crystal plasticity finite element (CPFE) code, PRISMS-Plasticity. The PRISMS-Plasticity model is a more precise determination of the local Schmid Factor and was used to simulate variations in slip and twin activity within each grain. Such simulations provide an avenue for physically interpreting the various slip traces observed in the dense DIC data and an improved understanding of the critical resolved shear stress of the various slip systems.
An open-source parallel 3-D crystal plasticity finite element (CPFE) software package PRISMS-Plas... more An open-source parallel 3-D crystal plasticity finite element (CPFE) software package PRISMS-Plasticity is presented here as a part of PRISMS integrated framework. A highly efficient rate-independent crystal plasticity algorithm is implemented along with developing its algorithmic tangent modulus. Additionally, a twin activation mechanism is incorporated into the framework based on an integration point sensitive scheme. The integration of the software as a part of the PRISMS framework is demonstrated. To do so, the integration of the PRISMS-Plasticity software with experimental characterization techniques such as electron backscatter diffraction (EBSD) and synchrotron X-ray diffraction using available open source software packages of DREAM.3D and Neper is elaborated. The integration of the PRISMS-Plasticity software with the information repository of Materials Commons is also presented. The parallel performance of the software is characterized which demonstrates that it scales well for large problems running on hundreds of processors. Various examples of polycrystalline metals with face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) crystals structures are presented to show the capability of the software to efficiently solve crystal plasticity boundary value problems, in addition to integration with preprocessing and postprocessing tools. PRISMS-Plasticity is an important activity within the broader PRISMS Center and future enhancements to PRISMS-Plasticity are planned and will be described.
Measurement and analysis of microstructures is an essential aspect of materials design and struct... more Measurement and analysis of microstructures is an essential aspect of materials design and structural performance. In the case of surface experimental measurements such as digital image correlation (DIC), it is beneficial to know the subsurface microstructure to interpret the surface observations accurately. However, subsurface microstructures are expensive to obtain through three-dimensional (3D) tomography. Hence, it is of interest to generate these structures computationally. In this work, a generalized inverse Voronoi problem is used to grow an approximate representation of the 3D microstructure from a surface electron backscatter diffraction (EBSD) image. The novelty of the approach is that the surface microstructure is retained during the simulation. This technique is employed for the reconstruction of a recrystallized magnesium alloy microstructure. Crystal plasticity finite element modeling (CPFEM) was employed for comparing the predicted surface strains in the reconstructed...
The Center for Predictive Integrated Structural Materials Science (PRISMS Center) is creating a u... more The Center for Predictive Integrated Structural Materials Science (PRISMS Center) is creating a unique framework for accelerated predictive materials science and rapid insertion of the latest scientific knowledge into next-generation ICME tools. There are three key elements of this framework. The first is a suite of high-performance, open-source integrated multi-scale computational tools for predicting microstructural evolution and mechanical behavior of structural metals. Specific modules include statistical mechanics, phase field, crystal plasticity simulation and real-space DFT codes. The second is the Materials Commons, a collaboration platform and information repository for the materials community. The third element of the PRISMS framework is a set of integrated scientific ''Use Cases'' in which these computational methods are linked with experiments to demonstrate the ability for improving our predictive understanding of magnesium alloys, in particular, the influence of microstructure on monotonic and cyclic mechanical behavior. This paper reviews progress toward these goals and future plans.
The critical energy release rate, defined as G c = 2γ+γ p (where γ is the cohesive energy and γ p... more The critical energy release rate, defined as G c = 2γ+γ p (where γ is the cohesive energy and γ p is the plastic work), is widely used as a macroscopic fracture criterion. During embrittlement of aluminum by gallium, impurity segregation is localized to a small region along the grain boundary and the bulk plastic properties are unaffected. Yet, the critical energy release rate (which is predominantly described by the plastic work [γ p ] since γ p > > γ) significantly decreases. In this work, we recognize that as the cohesive energy (γ) decreases during corrosion due to an increase in impurity concentration, the stress needed at the notch tip to form the crack decreases, and this, in turn, decreases the plastic work by reducing dislocation emission at the notch tip. We study two different models proposed in the past that can capture this dependence of γ p on γ during liquid metal (Ga) embrittlement of aluminum alloy (Al 7075). The parameters in these models are computed from first principles atomistic calculations and recent experiments. We compare and contrast these models on their ability to describe various aspects of embrittlement such as fracture toughness, K IC , and subcritical value of stress intensity, K Iscc. Extension of the approach to predict threshold fatigue crack initiation in Al7075 is suggested.
Lightweight materials such as Aluminum are prevalent in aerospace and automotive vehicles, but th... more Lightweight materials such as Aluminum are prevalent in aerospace and automotive vehicles, but the use of lighter Magnesium alloys will significantly increase fuel efficiency and cut emissions. Magnesium alloys present a wide array of unsolved scientific challenges, such as the deformation response of the slip and twin systems and the influence of dislocation interactions and twinning on tensile and fatigue behavior. In this thesis, a parallel three-dimensional(3D) crystal plasticity finite element opensource code was developed based on the deal.II finite element framework as part of PRISMS-Plasticity. Rate-independent crystal plasticity was implemented by developing a nonlinear algorithm which enables all the slip systems to lie on or inside the yield surface, and a consistent tangent modulus ensures convergence for small loading increments. A twin activation mechanism was incorporated into the framework based on a quadrature point sensitive scheme. Furthermore, by bounding the L-n...
Abstract The present work addressed the effects of heat treatment on the mechanical response of a... more Abstract The present work addressed the effects of heat treatment on the mechanical response of a WE43 Mg alloy using an integrated framework of SEM-DIC experiment and CPFE simulation. Both macroscopic responses including yield strength, ultimate strength, ductility, and microscopic responses, including local displacement and strain maps, were experimentally investigated. The focus of this work is to use the CPFE simulation as an integrated computational tool to study the effects of heat treatment. The CPFE framework was evaluated using the local fields of displacement and strain obtained from the SEM-DIC experiment rather than the conventional scheme of using macroscopic responses at different loading directions. Subsequently, the information which is available using CPFE, such as the critical resolved shear stress (CRSS) and relative slip activity, was used to study the effects of heat treatment on the response of WE43 Mg alloy. The contributions of different strengthening mechanisms on the CRSS were addressed. The results show that effects of heat treatment can be captured using the predominant mechanisms of the grain size effect and the influence of precipitates. Finally, it has been shown that classical Hall-Petch in which one constant can capture the size effects, should be modified. To do so, each deformation mode should have a unique Hall-Petch constant, which are calculated here for the WE43 Mg alloy.
The effect of aging on the accumulation of microscale plasticity, and the resulting macroscopic m... more The effect of aging on the accumulation of microscale plasticity, and the resulting macroscopic mechanical behavior, were examined in the magnesium alloy WE43 under uniaxial tension. Full-field strains on the length scale of the microstructure, and their relation to the underlying crystallography, were captured using a combination of electron backscatter diffraction, custom nanoparticle patterning processes for corrosion-susceptible alloys, scanning electron microscopy (SEM), in-SEM uniaxial tensile and compressive loading, and distortion-corrected digital image correlation. The as-received material exhibited an average grain size of 12 μm. The strain incurred on individual slip traces in magnesium was resolved for the first time. Insights into slip activation across the microstructure revealed that using Schmid's Law with the nominal Schmid Factor appeared to be predictive for basal and non-basal slip. The DIC results were compared with simulation using an advanced open-source crystal plasticity finite element (CPFE) code, PRISMS-Plasticity. The PRISMS-Plasticity model is a more precise determination of the local Schmid Factor and was used to simulate variations in slip and twin activity within each grain. Such simulations provide an avenue for physically interpreting the various slip traces observed in the dense DIC data and an improved understanding of the critical resolved shear stress of the various slip systems.
An open-source parallel 3-D crystal plasticity finite element (CPFE) software package PRISMS-Plas... more An open-source parallel 3-D crystal plasticity finite element (CPFE) software package PRISMS-Plasticity is presented here as a part of PRISMS integrated framework. A highly efficient rate-independent crystal plasticity algorithm is implemented along with developing its algorithmic tangent modulus. Additionally, a twin activation mechanism is incorporated into the framework based on an integration point sensitive scheme. The integration of the software as a part of the PRISMS framework is demonstrated. To do so, the integration of the PRISMS-Plasticity software with experimental characterization techniques such as electron backscatter diffraction (EBSD) and synchrotron X-ray diffraction using available open source software packages of DREAM.3D and Neper is elaborated. The integration of the PRISMS-Plasticity software with the information repository of Materials Commons is also presented. The parallel performance of the software is characterized which demonstrates that it scales well for large problems running on hundreds of processors. Various examples of polycrystalline metals with face-centered cubic (FCC), body-centered cubic (BCC), and hexagonal close-packed (HCP) crystals structures are presented to show the capability of the software to efficiently solve crystal plasticity boundary value problems, in addition to integration with preprocessing and postprocessing tools. PRISMS-Plasticity is an important activity within the broader PRISMS Center and future enhancements to PRISMS-Plasticity are planned and will be described.
Measurement and analysis of microstructures is an essential aspect of materials design and struct... more Measurement and analysis of microstructures is an essential aspect of materials design and structural performance. In the case of surface experimental measurements such as digital image correlation (DIC), it is beneficial to know the subsurface microstructure to interpret the surface observations accurately. However, subsurface microstructures are expensive to obtain through three-dimensional (3D) tomography. Hence, it is of interest to generate these structures computationally. In this work, a generalized inverse Voronoi problem is used to grow an approximate representation of the 3D microstructure from a surface electron backscatter diffraction (EBSD) image. The novelty of the approach is that the surface microstructure is retained during the simulation. This technique is employed for the reconstruction of a recrystallized magnesium alloy microstructure. Crystal plasticity finite element modeling (CPFEM) was employed for comparing the predicted surface strains in the reconstructed...
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Papers by Sriram Ganesan