OOF: Finite Element Analysis of Microstructures

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The OOF Project

OOF1.1 is public domain software created at the National Institute of Standards and Technology (NIST) to investigate the properties of microstructures. The microstructure of a material is the (usually) complex ensemble of polycrystalline grains, second phases, cracks, pores, and other features occurring on length scales large compared to atomic sizes.

At the simplest level, OOF is designed to answer questions like, ``I know what this material looks like and what it's made of, but I wonder what would happen if I pull on it in different ways?'', or ``I have a picture of this stuff and I know that different parts expand more than others as the temperature increases -- I wonder where the stresses are greatest?''

One approach for investigating microstructural behavior is to reduce the representation of a microstructure to a small number of physical parameters (such as grain size or porosity) and develop a model which depends on them. If this type of reductionist approach is predictive, then such models can be extremely useful. However, when physical properties depend on microstructural details (such as the spatial correlation of crystallite orientation, the shapes and dispersion of second phases, extremes of statistical distributions, or local anisotropies) such data reduction is often difficult or pointless.

OOF takes a non-reductionist, brute force approach, but in a user-friendly way. The user starts with a digitized image of the microstructure and builds a data structure on top of it. All the data plus any that can be inferred by the user is used. Tools are provided to allow the user to graphically select features in the microstructural image and specify their properties. For OOF, the microstructure is a data structure composed of image and property data.

The idea of basing calculations on images is not new. Edward Garboczi and colleagues at NIST have used this approach to investigate behavior of cements and porous media. Researchers at Alcoa have developed finite element models of textured materials. The purpose of creating OOF and distributing it freely is to supply a generic tool for calculating microstructure-property relations.

Currently, there are two versions of OOF. The original version solves thermoelastic problems with a constant temperature field. The ``thermal'' version of OOF solves for temperature and elastic displacement simultaneously. Work is underway on a completely new version of OOF which will be more easily extendible to other types of physical properties. Users will be able to design their own materials and to include them into the OOF source. Our ambition is that people will use OOF to do types of research that we have not imagined.

The OOF Project actually consists of two programs. PPM2OOF reads images and assigns material properties to them, and OOF reads the output from PPM2OOF and performs virtual experiments on it. This manual describes only the latter program. OOF can be used independently of PPM2OOF, as long as OOF is provided with a data file in the format described in Section 6.3.

This manual mainly describes the original version of OOF. Differences between the original, elasticity-only OOF and the thermal version are described in Section [*].

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