scope:

Purpose

This NASA Technical Handbook covers recommended material removal processes (i.e., machining or grinding) for advanced ceramics and glasses, which are referred to as "ceramics" in this Handbook. It is applicable to both test specimens and components, hereafter referred to as "specimens." This Handbook is not intended to replace or supersede customary (e.g., internally accepted or proprietary) or application-matched machining/grinding practices. Instead, it is intended to provide recommended material removal procedures developed from experience and testing, and thereby ensure consistent test specimen and component performance. Geometries addressed in this Handbook include prismatic sections, flat plates (disks and square plates), and cylindrical rods. Grinding parameters, including diamond (abrasive)-grit size and material removal rates, are addressed in addition to cutting fluid type and conditions. Appendix A, Recommended Polishing Specifications for Ceramic Windows, provides a specific application example.

Fabrication of test specimens and components can introduce dimensional variations, subsurface damage, and residual stresses which may have pronounced effects on measured mechanical properties and behavior. Because universal or standardized procedures for surface preparation do not exist, guidance on specimen preparation is useful to ensure that such variations are minimized in determining material properties such as ultimate strength. The procedures described in this Handbook address some of the factors responsible for machining effects. It should be understood that final machining steps may or may not negate machining damage introduced during the initial steps. Therefore, measures like surface roughness alone of the specimen may not be adequate for determining ultimate strengths of advanced ceramics. Specimen fabrication processes should be controlled and reported with the goal of minimizing subsurface damage.

Although careful visual inspection of components is recommended, it may or may not reveal inappropriate machining, handling, and contaminant subsurface damage.

Handling of test specimens and components can introduce damage significantly in excess of the damage produced by common fabrication practices. Specimens and components must be handled carefully. Appendix C, Examples of Handling and Machining Related Damage, provides examples of damage and recommendations to avoid such problems.

This Handbook may be used for material development, material comparison, quality assurance, characterization, and design data generation.