DEPARTMENT OF ENERGY: NATIONAL NUCLEAR SECURITY ADMINISTRATION
The Center for Research Excellence on Dynamically Deformed Solids (CREDDS) aims to discover, understand, and predict the influence of microstructural heterogeneities—such as interfaces, inclusions, and porosity—on the high strain rates mechanical response of additively manufactured, multiphase metallic materials. CREDDS brings together four leading US universities—Texas A&M University (TAMU, lead institution), U. of Michigan (UM), UC Santa Barbara (UCSB), and U. Connecticut (UConn)—with student-centered research activities coordinated with National Nuclear Security Administration (NNSA) laboratories, including LANL and LLNL. UCONN is responsible for atomic scale modeling of the deformation and failure response using classical molecular dynamics simulations to investigate the role of variations in the microstructure on the predicted deformation and failure response under shock loading conditions. The aim will be to understand the evolution of defects (dislocations) during shock compression as well as the evolution of damage (voids) at the atomic scales and discover the physical mechanisms by which interfaces (both homo- and heterophase), inclusions, pores, and other microstructural inhomogeneities respond to high strain-rate deformation.
NATIONAL SCIENCE FOUNDATION (NSF): GOALI
The design/discovery of layered materials for applicability in next-generation battery technologies requires a fundamental understanding of the links between the atomic scale structure, chemistry and the mechanisms and energetics of intercalation and de-intercalation reactions. The goal of the proposed research is to design/discover layered (2D) material microstructures as alternatives to graphite and Li ions using an innovative combination of atomic scale modeling, experimental in-situ characterization of the microstructural evolution during (de)intercalation reactions and use of machine learning methods to unravel the potential of layered materials for battery applications. Density functional theory (DFT) simulations will aim to investigate the links between the bonding environments and structural accommodation of the layered material during insertion and exertion of the intercalating species (energy barriers, volumetric expansion, and phase transformations and the role of defects, doping, and interfaces) to understand the cycling stability for various microstructures. This program is led by Prof. C. Barry Carter at UConn and aims to use in-situ characterization using high resolution transmission electron microscopy (HRTEM) to characterize the dynamic evolution of microstructure during these solid-state reactions and validate the modeling based results. This GOALI project also involves Dr. Arthur Dobley as a co-PI with EaglePicher LLC as an industry partner.
US ARMY RESEARCH LABORATORY: WIRE ARC ADDITIVE MANUFACTURING PROGRAM
This program is in support of the manufacturing sciences program led by VRC Metal Systems LLC and involves performing modeling of evolution of microstructure and residual stresses during WAAM at the University of Connecticut (UConn). The mesoscale approaches used will be the mesoscale quasi-coarse-grained dynamics (QCGD) method developed by co-PI Dongare and a phase field framework based on COMSOL Multiphysics solver. The following tasks will aim to correlate with the microstructure characterized experimentally in the group of Prof. Mark Aindow (PI). The mechanism of the formation of dendrites during the solidification of the melt pool will be investigated using QCGD simulations. These simulations will model the evolution of solid-liquid interfaces during solidification and the evolution of chemical segregation during growth of dendrites for the thermal gradients observed/predicted during WAAM. The QCGD simulations will aim to investigate the size of the dendrites and the compositional distribution in the dendrites, as well as the local distributions of stresses for variations in temperature gradients.
OFFICE OF NAVAL RESEARCH / BROWN UNIVERSITY
The mechanical behavior of fiber-reinforced polymer (FRP) composites is determined by the ability of the fiber-matrix interface to distribute the load from the matrix to the reinforcing fiber. The response of these materials in marine environments, in addition, is complicated by the hygrothermal effects at the interface that modify the strength and fracture toughness characteristics of FRPs. The proposed effort will aim to use classical molecular dynamics (MD) simulations to investigate the role of absorbed water on the modifications in fiber/matrix interface strengths as well as on the high
strain rate deformation behavior. MD simulations will be carried out to investigate the high strain rate behavior of such interfaces under multiaxial loading conditions to enable parameterization of the high-rate constitutive behavior of the FRPs and the modifications due to the presence of water saturation.
US ARMY RESEARCH LABORATORY: COLD SPRAY MODELING PROGRAM
The cold spray process involves acceleration of metal particles at supersonic velocities on to a metal substrate. The impact results in severe plastic deformation of the particle and the substrate, and in-turn, bonding of the particle to the substrate. This impact-induced bonding of metal particles forms the basis of the process for coating, repair and additive manufacturing technologies. A critical challenge in the development and optimization of the cold spray process is the current understanding of the dynamic evolution of the microstructure during particle impact. The short time scales (microseconds) and length scales (tens of microns) involved make it extremely challenging to characterize these mechanisms using experiments. The focus of this program aims to model the impact of Al particles with sizes up to tens of microns on to a metal substrate and enable the investigation of the dynamic evolution of microstructure during impact using a newly developed ‘quasi-coarse-grained dynamics’ (QCGD) method. This effort is combined with experimental approaches to investigate the cold spray of precipitation-hardened Al alloys from gas atomized powder feedstocks. This is part of a major multi-institution ARL-funded program aim of this program is to develop robust processing-microstructure-property models for cold-sprayed Al alloys.
The program aims to model the microstructure evolution of Ti powders during laser additive manufacturing at the mesoscales. The mesoscale modeling is carried out using a hybrid mesoscale-continuum method that combines the quasi-coarse-grained dynamics method with a two-temperature model. . The hybrid QCGD-TTM approach retains the laser energy absorption, heat generation/transfer, and microstructure evolution (melting, defects, and damage) behavior predicted by atomic-scale simulations. The program will extend this capability to model the α/β microstructure in polycrystalline Ti alloy powders and investigate role of laser parameters on kinetics of solid-liquid interface during melting and the role of ablation.
NATIONAL SCIENCE FOUNDATION (NSF): FACULTY EARLY CAREER DEVELOPMENT AWARD (CAREER)
The five year CAREER grant supports research on advancing the understanding of the factors that control the evolution of defects and their structure, the micromechanisms for their evolution, and their collective influence on material performance. The objective of this research is to establish insight into the effects of microstructure and loading conditions on the micromechanisms responsible for the nucleation, accumulation, and interaction of defect structures (dislocations, twins, interfaces) as well as nucleation, growth, and coalescence of voids to form cracks (damage). The research employs a newly developed ‘quasi-coarse-grained dynamics’ (QCGD) method that is able to retain the atomic scale physics of processes involved during deformation and failure but extends the time and length scale capabilities of molecular dynamics simulations. algorithms will be used to map the evolution and distribution of defect structures to the macroscale stress-strain response and identify the distributions that trigger critical events such as damage initiation. This will allow direct connections between the microstructural evolution during deformation and the strength and toughness response for structural metallic materials.
US ARMY RESEARCH OFFICE: SOLID MECHANICS PROGRAM
The goal of the proposed research program is to develop microstructure-failure-strength relationships at mesoscales in lightweight metallic systems under dynamic loading conditions and bridge the gap between atomistic and continuum simulations. To achieve this goal, a novel mesoscale modeling method called quasi-coarse-grained dynamics (QCGD) is developed that extends the time and length scale capabilities of MD simulations in the mesoscales. The mesoscale behavior is enabled by choosing representative atoms to model the dynamics of several atoms in an atomic scale microstructure. Scaling relationships are used to retain the energetics and the atomic scale degrees of freedom for these representative atoms as well as the missing atoms. The proposed quasi-coarse-grained dynamics (QCGD) method allows larger size systems and improved time-steps for simulations and is thus able to extend the capabilities of MD simulations to model materials behavior at mesoscales. The proposed research will develop a computationally efficient mesoscale model capable of reproducing the thermodynamic, mechanical, and wave propagation behavior in polycrystalline Al, Mg and Ti microstructures and identify the links between microstructure and failure-strength at mesoscales and bridge the gap between atomic simulations and continuum simulations.
US ARMY RESEARCH OFFICE: DURIP
The current capabilities in any computational group is limited to the post-processing of data using software and visualization methods that are limited by our instincts as well as the 2D images rendered by the visualization methods. The current simulation sizes using MD/QCGD simulations comprises of systems that are greater than 100 Million atoms and the amount of data generated for various simulations limits the analysis of these micromechanisms. The detailed analysis of this Big Data is the current bottleneck in the understanding of the links between the atomic scale structures and the response of materials in various environments. As a result, the DURIP award will develop/use data analytics and virtual reality (VR) based visualization equipment to analyze these data sets. The analysis and visualization will aim to identify the links between the atomic scale structure of the key microstructural features (bonding environments, atomic radii, strains, dimensions, distributions, etc.) such as grain boundaries, interfaces, etc., the dynamic evolution of defects/interfaces and the resultant performance metrics computed using the simulations. 3D visualization of the data will be used to validate these descriptors and identify key mechanisms responsible for the predicted materials response.
US ARMY RESEARCH LABORATORY: COMPUTATIONAL & INFORMATION SCIENCES DIRECTORATE
The goal of this program is to gain a fundamental understanding of the relationship between the atomic scale structure, chemistry, strain and the electronic properties of various configurations of stacked 2D materials using atomistic simulations (density functional theory and mole. The proposed research program aims to investigate the electronic properties of various 2D layered nanostructures using density functional theory (DFT) calculations so as to investigate the strain response of monolayer and few-layered structures of 2D materials (MoS2, ReS2, HfS2). In addition, the role of edges is being investigated on the observed electronic response of CVD-grown structures under applied strain. In addition, the molecular dynamics simulations are being carried out to investigate the strain relaxation behavior of CVD-growth structures.
PRATT & WHITNEY: UCONN ADDITIVE MANUFACTURING INNOVATION CENTER
The proposed research addressed the question how variations in powder pedigree and temperature maxima during additive manufacturing affect the melting behavior of Ti-6Al-4V powder beds. The melting and fusion stage during which the powder bed locally transforms into a liquid pool largely determines the formation of defects such as voids, pores, or un-melted regions in the final product. The fusion of powder particles depends on the viscosity of the liquid alloy, the surface energies, capillary effects, and hence implicitly on the composition, temperature, and atmosphere. Alloy powder compositions, including impurities, change with the number of recycles, but also due to batch-to-batch variations and differences in composition specifications from different powder vendors. Large scale molecular dynamics simulations were carried out to compute the viscosity of Ti powder particles as well as to investigate the phenomena of melting and the propagation of the melt-front.