HANDBOOK FOR RECOMMENDED MATERIAL REMOVAL PROCESSES FOR ADVANCED CERAMIC TEST SPECIMENS AND COMPONENTS
|Publication Date:||17 July 2018|
The purpose of this NASA Technical Handbook is to cover recommended material removal processes (i.e., machining or grinding) for advanced ceramics and glasses, which are referred to as "ceramics" in this NASA Technical Handbook. It is applicable to both test specimens and components, hereafter referred to as "specimens." This NASA Technical 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 NASA Technical 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 NASA Technical 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 NASA Technical Handbook may be used for material development, material comparison, quality assurance, characterization, and design data generation.
This NASA Technical Handbook is applicable to material removal processes (machining or grinding) for advanced ceramics and glasses, which are referred to as "ceramics" in this NASA Technical Handbook. It is applicable to both test specimens and components, which are referred to in this NASA Technical Handbook as "specimens."
This NASA Technical Handbook is approved for use by NASA Headquarters and NASA Centers and Facilities. It may also apply to the Jet Propulsion Laboratory (a Federally Funded Research and Development Center (FFRDC)), other contractors, recipients of grants and cooperative agreements, and parties to other agreements only to the extent specified or referenced in their applicable contracts, grants, or agreements.
This NASA Technical Handbook, or portions thereof, may be referenced in contract, program, and other Agency documents for guidance.
The practice of material removal (machining or grinding) for advanced ceramics may involve hazardous materials, operations, and equipment. This test method does not purport to address the safety problems associated with its use. It is the responsibility of the user of this practice to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Contact the Center's Occupational Health Office for guidance.
This NASA Technical Handbook is intended primarily for use with advanced ceramics and glasses that "macroscopically exhibit" isotropic, homogeneous, continuous behavior. While this practice is intended for use on monolithic advanced ceramics and optical materials, certain whisker- or particle-reinforced composite ceramics as well as certain discontinuous fiberreinforced composite ceramics may also meet these macroscopic behavior assumptions. Generally, continuous fiber ceramic composites (CFCCs) do not macroscopically exhibit isotropic, homogeneous, continuous behavior; so application of this practice may not be appropriate.
Values expressed in this NASA Technical Handbook are in accordance with IEEE/ASTM SI 10™-2016, American National Standard for Metric Practice.