Mechanical properties of interest include stress-strain response (in multiple directions due to the anisotropic nature of the materials), first matrix cracking and ultimate strengths, thermal mechanical fatigue behaviour, elastic constants, interlaminar shear strengths, creep deformation, and fracture resistance due to various fracture modes.
Standardized test methods are essential not only for verification of micro-mechanical models but also in utilization of composite materials in component designs. Standardized test methods have been developed for fiber-reinforced polymer (FRP) composites by organizations such as the American Society for Testing and Materials (ASTM).
Many of the lessons learned in testing and implementing FRPs can be extended to CFCCs. However, the unique nature of CFCCs (a brittle matrix with a stiffness similar to or greater than the reinforcing brittle fibers) prevents the direct adoption of FRP test standards.
Ceramic Composites
In developing special standardized test methods for CFCCs, ASTM established Subcommittee C28.07 "Ceramic Composites" in June 1991 as an extension of Committee C28 "Advanced Ceramics." The group's first semiannual meeting of 1994 was held in January in Cocoa Beach, Florida, in conjunction with the American Ceramic Society's annual meeting on ceramic composites. The chairing group includes representatives of universities, national laboratories, and industry.
Although the subcommittee's scope encompasses development of test standards for all ceramic composites--including particulate, whisker, and fiber-reinforced--it is generally believed that test methods developed by other subcommittees for monolithic ceramics are applicable to particulate and whisker-reinforced composites. Therefore, the primary emphasis of C28.07 will continue to focus on developing test standards for CFCCs.
First Test Standard
A significant milestone was marked when the Society approved its first test standard--room temperature tensile testing. The success of the proposed standard practice reflects the strength of the document in addressing testing needs of the academic, research, and industrial participants in the ASTM standards process.
Introduction of the proposed standard practice on tensile testing as a national test method fulfills the top testing priority of the CFCC program's industrial participants. Priorities were formulated to reflect results of a 1992 survey.
The group's primary work is conducted not on the subcommittee level but on the task group level. Seven task groups have been formed since June 1993 to address the CFCC program's top testing priorities, NASA's Enabling Propulsion Materials, and Integrated High Performance Turbine Engine Technology. The table lists the various task groups, the task group focus, and membership.
Workshop Planned
At its January meeting, the subcommittee announced plans for two significant efforts. The first, "Workshop on Thermal and Mechanical Test Methods and Behavior of Continuous Fiber Ceramic Composites (CFCCs)," is planned for June 22, 1994, in conjunction with the C28 committee meetings in Montreal.
The second effort, "Symposium on Thermal and Mechanical Test Methods and Behaviour of Continuous Fiber Ceramic Composites (CFCCs)," is planned for the January 1996, C28 committee meeting in Cocoa Beach, Florida, in conjunction with the American Ceramic Society meeting on ceramic composites.
Introductory Meeting
An unofficial introductory meeting of the International Standards Organization's (ISO's) technical committee, TC206 (Fine Ceramics), was held in conjunction with the November 1993 American Ceramic Society PACRIM (Pacific Rim) meeting in Honolulu.
At the meeting, the secretariat of TC206 noted that membership of the technical committee consists of 8 participant members--Australia, Indonesia, Jamaica, Japan, Korea, Malaysia, Russia, and the United States--and 23 observer nations including most of Europe.
The scope of committee activities is along the lines already laid out by the European Community in its standardization process, i.e., premarket penetration normalization, or as the ISO terms it, early stage standardization.
Coordination of efforts to propose standards is on the committee's work agenda. The first plenary meeting of TC206 will be in Tokyo in May 1994. This is around the same time the "Fifth International Symposium on Ceramic Materials and Components for Engines" is to be held in Shanghai, China.
Subcommittee members indicated during the C28.07 meeting that they are interested in participating in ISO activities. Asked about taking a leadership role in TC206 activities, members indicated less interest.
GATT Dispute
An important aspect of establishing international standards is in the area of international trade. In the case of a GATT (General Agreement on Tariffs and Trade) dispute, the treaty requires the first recourse to be ISO standards. If no ISO standard exists, national standards will be employed. Thus, it may assist U.S. industry to encourage formulation of ISO standards that are similar to U.S. standards.
Because of the European commitment to premarket normalization, U.S. industry should be aware that near-term standards activities which precede introduction of CFCC products in the marketplace will speed the long-term acceptance and profitability of CFCCs.
International Marketing
Questioned about developing international markets for CFCCs or products containing CFCCs, industrial participants on the subcommittee indicated that such markets were far enough in the future that it is difficult to formulate a position on the issue. Industrial representatives included Allied Signal (R&D and Garrett), Babcock and Wilcox, DuPont, GE Aircraft Engines, Instron, Loral Vought Systems, Materials Science Corporation, MTS Systems, Norton Advanced Ceramics, Osram-Sylvania, Rolls Royce, and Solar Turbines.
The leadership urged the subcommittee to play a key role in ensuring that the
U.S. is both an active participant and a leader in extending test methods
developed for the U.S. into the international arena.
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Comments to: mgc@ornl.gov
Revised: July 5, 1995