NASA-HDBK-6007

Abstract

<strong>Purpose</strong> <br>This handbook covers recommended material removal processes (i.e., machining or grinding) for advanced ceramics. It is applicable to both test specimens and components, and hereafter they will be referred to as "specimens." This handbook is not intended to replace or supercede 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 standard practice 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 provides a specific application example, namely: Recommended Polishing Specifications for Ceramic Windows. <br>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. <br><strong>Applicability</strong> <br>This handbook may be referenced in contract, program, and other Agency documents for guidance. Individual portions of this handbook may be tailored (i.e., modified or deleted) by contract or program specifications to meet specific program/project needs and constraints. Tailoring must be formally documented and approved as part of program/project requirements. <br><em><strong>This practice 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.</strong></em> <br>This practice is intended primarily for use with advanced ceramics and optical materials 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 fiber-reinforced composite ceramics may also meet these macroscopic behavior assumptions. Generally, continuous fiber ceramic composites (CFCCs) do not macroscopically exhibit isotropic, homogeneous, continuous behavior; and application of this practice may not be appropriate. <br>Values expressed in this handbook are in accordance with the International System of Units (SI) and American Society for Testing and Materials (ASTM) SI10. <b><u>Intended Use:</u></b> This recommended practice is intended for use in fabricating ceramic test specimens or engineering components when customary, application, or other machining procedures are not applicable or available. <br>