Publications

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Computational simulation of structures subjected to blast loadings requires integration of computational shock-physics for blast, and structural response with potential for pervasive failure. Current methodologies for this problem space are problematic in terms of e ffi ciency and solution quality. This report details the development of several coupling algorithms for thin shells, with an emphasis on rigorous verification where possible and comparisons to existing methodologies in use at Sandia.

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This document compares the finite element shell formulations in the Sierra Solid Mechanics code. These are finite elements either currently in the Sierra simulation codes Presto and Adagio, or expected to be added to them in time. The list of elements are divided into traditional two-dimensional, plane stress shell finite elements, and three-dimensional solid finite elements that contain either modifications or additional terms designed to represent the bending stiffness expected to be found in shell formulations. These particular finite elements are formulated for finite deformation and inelastic material response, and, as such, are not based on some of the elegant formulations that can be found in an elastic, infinitesimal finite element setting. Each shell element is subjected to a series of 12 verification and validation test problems. The underlying purpose of the tests here is to identify the quality of both the spatially discrete finite element gradient operator and the spatially discrete finite element divergence operator. If the derivation of the finite element is proper, the discrete divergence operator is the transpose of the discrete gradient operator. An overall summary is provided from which one can rank, at least in an average sense, how well the individual formulations can be expected to perform in applications encountered year in and year out. A letter grade has been assigned albeit sometimes subjectively for each shell element and each test problem result. The number of A's, B's, C's, et cetera assigned have been totaled, and a grade point average (GPA) has been computed, based on a 4.0-system. These grades, combined with a comparison between the test problems and the application problem, can be used to guide an analyst to select the element with the best shell formulation.

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Model-based computer simulations have revolutionized product development in the last 10 to 15 years. Technologies that have existed for many decades or even centuries have been improved with the aid of computer simulations. Everything from low-tech consumer goods such as detergents, lubricants and light bulb filaments to the most advanced high-tech products such as airplane wings, wireless communication technologies and pharmaceuticals is engineered with the aid of computer simulations today. In this paper, we present a framework for describing computational tools and their application within the context of product engineering. We examine a few cases of product development that integrate numerical computer simulations into the development stage. We will discuss how the simulations were integrated into the development process, what features made the simulations useful, the level of knowledge and experience that was necessary to run meaningful simulations and other details of the process. Based on this discussion, recommendations for the incorporation of simulations and computational tools into product development will be made.

Failure modeling is inherently a multi length scale phenomenon that requires a failure model and a computational method that solves for stress/strain gradients at interesting locations. Focusing on the computational method, we recognize that the mesh resolution must be relatively fine in regions where failure is expected and relatively coarse elsewhere. Furthermore, in some modeling approaches the topology in the structural model is different than that required in the fine scale model where failure is to be predicted. This necessarily precludes approaches such as h-adaptivity. We are therefore led to consider multiscale approaches to solve these problems.This work describes an approach to solve multiple (a reference scale and fine scale) coupled boundary value problems for the purpose of nonlinear quasistatic stress analysis. Two examples are included: one example illustrates the multiscale solution strategy to perform quasistatic stress analysis and the other demonstrates the computational beginnings of the ability to model material failure.

An effort is underway at Sandia National Laboratories to develop a library of algorithms to search for potential interactions between surfaces represented by analytic and discretized topological entities. This effort is also developing algorithms to determine forces due to these interactions for transient dynamics applications. This document describes the Application Programming Interface (API) for the ACME (Algorithms for Contact in a Multiphysics Environment) library.

The Lubkin solution for two spheres pressed together and then subjected to a monotonically increasing axial couple is examined numerically. The Deresiewicz asymptotic solution is compared to the full solution and its utility is evaluated. Alternative approximations for the Lubkin solution are suggested and compared. One approximation is a Pade rational function which matches the analytic solution over all rotations. The other is an exponential approximation that reproduces the asymptotic values of the analytic solution at infinitesimal and infinite rotations. Finally, finite element solutions for the Lubkin problem are compared with the exact and approximate solutions.

An effort is underway at Sandia National Laboratories to develop a library of algorithms to search for potential interactions between surfaces represented by analytic and discretized topological entities. This effort is also developing algorithms to determine forces due to these interactions for transient dynamics applications. This document describes the Application Programming Interface (API) for the ACME (Algorithms for Contact in a Multiphysics Environment) library.

Frictional energy dissipation in joints is an issue of long-standing interest in the effort to predict damping of built up structures. Even obtaining a qualitative understanding of how energy dissipation depends on applied loads has not yet been accomplished. Goodman postulated that in harmonic loading, the energy dissipation per cycle would go as the cube of the amplitude of loading. Though experiment does support a power-law relationship, the exponent tends to be lower than Goodman predicted. Recent calculations discussed here suggest that the cause of that deviation has to do with reshaping of the contact patch over each loading period.

The Microsystems Subgrid Physics project is intended to address gaps between developing high-performance modeling and simulation capabilities and microdomain specific physics. The initial effort has focused on incorporating electrostatic excitations, adhesive surface interactions, and scale dependent material and thermal properties into existing modeling capabilities. Developments related to each of these efforts are summarized, and sample applications are presented. While detailed models of the relevant physics are still being developed, a general modeling framework is emerging that can be extended to incorporate evolving material and surface interaction modules.

An effort is underway at Sandia National Laboratories to develop a library of algorithms to search for potential interactions between surfaces represented by analytic and discretized topological entities. This effort is also developing algorithms to determine forces due to these interactions for transient dynamics applications. This document describes the Application Programming Interface (API) for the ACME (Algorithms for Contact in a Multiphysics Environment) library.

An effort is underway at Sandia National Laboratories to develop a library of algorithms to search for potential interactions between surfaces represented by analytic and discretized topological entities. This effort is also developing algorithms to determine forces due to these interactions for transient dynamics applications. This document describes the Application Programming Interface (API) for the ACME (Algorithms for Contact in a Multiphysics Environment) library.