Standardization Efforts for Mechanical Testing and Design of Advanced Ceramic Materials and Components

ABSTRACT Advanced aerospace systems occasionally require the use of very brittle materials such as sapphire andultra-high temperature ceramics. Although great progress has been made in the development of methods andstandards for machining, testing and design of component from these materials, additional development anddissemination of standard practices is needed. ASTM Committee C28 on Advanced Ceramics and ISO TC 206 havetaken a lead role in the standardization of testing for ceramics, and recent efforts and needs in standardsdevelopment by Committee C28 on Advanced Ceramics will be summarized. In some cases, the engineers, etc.involved are unaware of the latest developments, and traditional approaches applicable to other material systems areapplied. Two examples of flight hardware failures that might have been prevented via education and standardizationwill be presented. INTRODUCTION Environmental and energy concerns (often bolstered by governmental regulations) have placed increasinglygreater demands on materials used in advanced engineering designs such as aerospace systems. For example, asgreater efficiencies are sought and achieved in the design of gas turbine engines, so too have the temperature,strength and weight requirements of their components changed to "push the limit" of the mechanical properties ofthe various materials (generally metallic alloys). Large amounts of time and effort have been devoted to the searchfor structural materials that will keep pace with these engineering demands. Often these searches identifyunderutilized materials that can be classified as “brittle.” In some cases, such as sapphire for windows, processingsuccesses (both primary and secondary) have led to the successful use of an advanced ceramic in demandingapplications [1]. In other cases, in spite of tremendous strides in understanding and processing materials, onlyrecently have structural ceramic materials, such as silicon nitrides or silicon carbide fiber-reinforced silicon carbidematrix composites, reached the developmental stage required to receive focused attention as plausible successors tothe more traditional metallic alloys [2]. The applications contemplated require optimum material behavior withphysical and mechanical property reproducibility, component reliability, and well-defined methods of data treatmentand materials analysis. As advanced ceramics are contemplated for introduction into advanced heat engine, theseissues are best dealt with via standard methods [2].A variety of organizations, such as ASTM, ISO, and the NASA TSP, are involved with the development ofstandards, and the standards developed by one organization often feed into the development of standards in anotherorganization. The American Society for Testing and Materials (ASTM) [a.k.a., ASTM International] is the primarystandards writing establishment in the United States. As a private, nonprofit corporation, ASTM relies upon thevoluntary cooperation of industry, government, and academe to develop standards by full consensus. ASTMCommittee C28 "Advanced Ceramics" was formed in 1986 when it became apparent that ceramics were beingconsidered for "high-tech" applications. More background on ASTM and its committees can be found at theorganization’s website.