Showing papers by "Stewart A. Silling published in 2022"
TL;DR: Nonlocal Kernel Network (NKN) as discussed by the authors is a nonlocal neural operator that is resolution independent, characterized by deep neural networks, and capable of handling a variety of tasks such as learning governing equations and classifying images.
30 citations
TL;DR: In this paper , the authors proposed a mesh-free peridynamics (PD) discretization scheme that employs a simple collocation procedure and is truly mesh free, i.e., it does not depend on any background integration cells.
26 citations
TL;DR: In this paper , a custom compression apparatus, suitable for integration with micro-computed tomography (micro-CT) system, was used to collect 3-D scans of a bulk powder at discrete steps of increasing compression.
Abstract: Powders under compression form mesostructures of particle agglomerations in response to both inter- and intra-particle forces. The ability to computationally predict the resulting mesostructures with reasonable accuracy requires models that capture the distributions associated with particle size and shape, contact forces, and mechanical response during deformation and fracture. The following report presents experimental data obtained for the purpose of validating emerging mesostructures simulated by discrete element method and peridynamic approaches. A custom compression apparatus, suitable for integration with our micro-computed tomography (micro-CT) system, was used to collect 3-D scans of a bulk powder at discrete steps of increasing compression. Details of the apparatus and the microcrystalline cellulose particles, with a nearly spherical shape and mean particle size, are presented. Comparative simulations were performed with an initial arrangement of particles and particle shapes directly extracted from the validation experiment. The experimental volumetric reconstruction was segmented to extract the relative positions and shapes of individual particles in the ensemble, including internal voids in the case of the microcrystalline cellulose particles. These computationally determined particles were then compressed within the computational domain and the evolving mesostructures compared directly to those in the validation experiment. The ability of the computational models to simulate the experimental mesostructures and particle behavior at increasing compression is discussed.
1 citations
TL;DR: In this article, a Bayesian framework for uncertainty quantification (UQ) in material response prediction when using nonlocal models was developed, which combines the nonlocal operator regression (NOR) technique and Bayesian inference.
Abstract: We consider the problem of modeling heterogeneous materials where micro-scale dynamics and interactions affect global behavior. In the presence of heterogeneities in material microstructure it is often impractical, if not impossible, to provide quantitative characterization of material response. The goal of this work is to develop a Bayesian framework for uncertainty quantification (UQ) in material response prediction when using nonlocal models. Our approach combines the nonlocal operator regression (NOR) technique and Bayesian inference. Specifically, we use a Markov chain Monte Carlo (MCMC) method to sample the posterior probability distribution on parameters involved in the nonlocal constitutive law, and associated modeling discrepancies relative to higher fidelity computations. As an application, we consider the propagation of stress waves through a one-dimensional heterogeneous bar with randomly generated microstructure. Several numerical tests illustrate the construction, enabling UQ in nonlocal model predictions. Although nonlocal models have become popular means for homogenization, their statistical calibration with respect to high-fidelity models has not been presented before. This work is a first step towards statistical characterization of nonlocal model discrepancy in the context of homogenization.
TL;DR: In this article , the effect of microstructure on the high-rate tensile failure of additively manufactured (AM) 304L stainless steel is analyzed using state-based peridynamics.
Abstract: The effect of microstructure on the high-rate tensile failure of additively manufactured (AM) 304L stainless steel is analyzed. The method uses state-based peridynamics with a new model for the time dependence of failure within grains. The model incorporates anisotropy in the elastic and plastic response of the grains. The grain shapes and lattice orientations are initialized directly from electron backscatter diffraction (EBSD) images. The model results are compared to test data from plate impact experiments over a range of impact velocities. A set of parameters for a homogenized material derived from the mesoscale model is demonstrated in the CTH hydrocode.
01 Sep 2022
TL;DR: In this article , the authors developed a mathematically rigorous and physically consistent interface theory and demonstrate its scope in mission-relevant exemplar problems, such as fracture mechanics for nuclear components and subsurface flow for nuclear waste disposal.
Abstract: Nonlocal models provide a much-needed predictive capability for important Sandia mission applications, ranging from fracture mechanics for nuclear components to subsurface flow for nuclear waste disposal, where traditional partial differential equations (PDEs) models fail to capture effects due to long-range forces at the microscale and mesoscale. However, utilization of this capability is seriously compromised by the lack of a rigorous nonlocal interface theory, required for both application and efficient solution of nonlocal models. To unlock the full potential of nonlocal modeling we developed a mathematically rigorous and physically consistent interface theory and demonstrate its scope in mission-relevant exemplar problems.
01 Apr 2022
TL;DR: In this paper , a straight curve with nonlocal forces that are independent of bond strain is considered and the equilibrium value of the radius of curvature is computed explicitly, where the internal loads can either stabilize or destabilize the straight con?guration.
Abstract: A straight ?ber with nonlocal forces that are independent of bond strain is considered. These internal loads can either stabilize or destabilize the straight con?guration. Transverse waves with long wavelength have unstable dispersion properties for certain combinations of nonlocal kernels and internal loads. When these unstable waves occur, deformation of the straight ?ber into a circular arc can lower its potential energy in equilibrium. The equilibrium value of the radius of curvature is computed explicitly.
01 Oct 2022
TL;DR: In this paper , the phase stability in native powder, as-built and annealed Ti-5553 through diamond anvil cell (DAC) and ramp compression experiments was investigated, and the effect of tensile loading on a sample containing an interface between a Ti-6Al-V4 (Ti-64) baseplate and additively manufactured titanium layer was explored.
Abstract: Additive manufactured Ti-5Al-5V-5Mo-3Cr (Ti-5553) is being considered as an AM repair material for engineering applications because of its superior strength properties compared to other titanium alloys. Here, we describe the failure mechanisms observed through computed tomography, electron backscatter diffraction (EBSD), and scanning electron microscopy (SEM) of spall damage as a result of tensile failure in as-built and annealed Ti-5553. We also investigate the phase stability in native powder, as-built and annealed Ti-5553 through diamond anvil cell (DAC) and ramp compression experiments. We then explore the effect of tensile loading on a sample containing an interface between a Ti-6Al-V4 (Ti-64) baseplate and additively manufactured Ti-5553 layer. Post-mortem materials characterization showed spallation occurred in regions of initial porosity and the interface provides a nucleation site for spall damage below the spall strength of Ti-5553. Preliminary peridynamics modeling of the dynamic experiments is described. Finally, we discuss further development of Stochastic Parallel PARticle Kinteic Simulator (SPPARKS) Monte Carlo (MC) capabilities to include the integration of alpha ( ? )-phase and microstructural simulations for this multiphase titanium alloy.