||Free Drawings Available from NIST of New Specimen in Revised ASTM Ceramics Method
ASTM Committee C28 on Advanced Ceramics has approved 26 revisions to ASTM C 1161, Standard Test Method for Flexural Strength of Advanced Ceramics. Now available, the revision will assist those who prepare ceramic bend bars for strength tests. Test Method C 1161 is used to measure ceramic strength in the specifications of Committees F04 on Surgical and Medical Devices, and F34 on Rolling Element Bearings.
According to industry sources, said George Quinn, a ceramic engineer with the National Institute of Standards and Technology, Gaithersburg, Md., who has been breaking ceramic bend bars for 33 years, 90 percent or more of the 1000-1500 flexural strength specimens that are prepared weekly in the United States conform to the B size (3 mm x 4 mm x 50 mm) in ASTM Standard C 1161. After 12 years on the books, this standard, which superseded an earlier MIL standard, was given a major overhaul to meet the emerging needs of the ceramic community.
Free engineering drawings of the new B specimens which include the new machining specifications are available from Quinn at the address below.
The revision discontinued the use of an obsolete 1/8 x 1/4 x 2 specimen, Quinn said. More guidance on the interpretation of fracture patterns was added to help users determine the origin location. The biggest change was a major revision to the standard specimen preparation procedure. The new surface grinding specifications include a requirement for final finish longitudinal grinding with diamond wheels between 400 to 600 grit as opposed to the former 320 to 500 grit range in the old C 1161 (1990) and the 200 to 500 grit range allowed by MIL STD 1942 (1983). The new finer finishing requirements are in response to industry requirements for strength test specimens that more closely match the finishes and preparation steps applied to components.
A member of committee C28, Quinn drafted the revision with broad input from ceramic research scientists and engineers, commercial users and producers. For example, he said, one major ceramic producer company was very keen on our adding a scratch check into the standard. Scratches are inadvertent faults on the test pieces and can ruin the experiment. Finely finished ceramic components and test pieces are susceptible to scratch damage. The company had been having trouble with this and went to great lengths to discover the source of the inadvertent damage.
On another score, the critical changes to the specimen-machining specifications in the standard were driven by the changes in the commercial marketplace, Quinn explained. Finer finishes are being applied to ceramics components in production, and the user community wanted the test pieces in the standard to have comparable finishes. Machine shops that prepared the specimens for their research and commercial users informed the C28 task group that the market was shifting in this direction as well. The machine shops also actively helped our committee revise the standard.
While this was all going on, some machining research studies here at NIST and also at Oak Ridge National Lab were generating new scientific information that supported the machining changes. Happiness is when researchers, users, and producers converge on a common solution.
For further technical information or to obtain the drawings, contact George Quinn, NIST, STOP 8521, Ceramics Division Bldg. 223 A329, Gaithersburg, MD 20899-8521 (phone: 301/975-5765) Committee C28 meets April 27-28 in St. Louis, Mo., in conjunction with the American Ceramics Society. For meeting or membership details, contact Gloria Collins, manager of ASTM Technical Committees (phone: 610/832-9715). //
Copyright 2002, ASTM