Data Evaluation Theory and Practice for Materials Properties

Schematic of a silicon carbide ceramic in an active atmosphere. Data evaluation must account for the complexity of polycrystalline materials and the resulting dependence of material properties on chemical composition, physical microstructure, and environmental conditions. Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. iii FOREWORD Data evaluation is the process by which collections of data are assessed with respect to reliability, completeness, and consistency. The present work addresses data evaluation for materials properties as a scientific discipline that evolves from the formal underpinnings of materials metrology. A theoretical foundation for data evaluation is developed and then illustrated in a practical application to the development of an operational protocol for materials property data. An extensive collection of examples is used to examine, in succession, the issues of accessibility, reproducibility, consistency, and predictability. Distinctions are made among definitive relations, correlations, derived and semiempirical relations, heuristic theories, and value estimates. Subtopics include the use of properties as parameters in models, the interpretation of ad hoc parameters, and the treatments of procedural properties, response dependent properties, and system dependent data. v Acknowledgments ◆ ACKNOWLEDGMENTS The collective understanding of the importance of data evaluation, particularly with respect to the use of materials property relations, has evolved significantly during the last decade. The author is especially mindful of the benefits derived during that time from numerous interactions with colleagues at NIST. A true list of the names of all the individuals who have been kind to me in this effort would, perhaps, comprise a veritable staff directory. At the risk of being accused of a certain lack of perspicacity, I would like to acknowledge explicitly a few of those people whose shared wisdom has been repeatedly useful to me: