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Significance Statement
The indentation fracture (IF) method has been one of the most popular mechanical tests for evaluation of fracture toughness of ceramics due to the simple and rapid test procedure. Especially in the ceramic industry, it is indispensable for both ranking the performances of tiny ceramic components such as bearing balls, cutting tools, dental materials etc. and their quality control because other test techniques of fracture toughness are not applicable to those small products. However, the low reproducibility of the method has been a critical issue, which hinders the standardization. In order to resolve the difficulty, we have proposed an improved indentation fracture method which reduces the error in reading crack lengths significantly. In this technique, each crack tip is clearly identified and centered in each high-resolution optical image using both an objective lens of 40× or 50× and a traveling stage, and crack lengths are measured accurately from the difference in the stage positions. Round-robin tests were conducted domestically and internationally to demonstrate the effectiveness of this simple and cost effective new approach. The coefficient of variance of the resultant indentation fracture resistance, KIFR was comparable to those typical of standard fracture toughness tests, confirming the reliability of the improved indentation fracture method.
Journal Reference
Ceramics International, Volume 41, Issue 10, Part A, December 2015, Pages 13271–13276.
Hiroyuki Miyazaki, ,Yu-ichi Yoshizawa
National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimo-shidami, Moriyama-ku, Nagoya 463-8560, Japan.
An international round-robin test on an improved indentation fracture (IF) method was conducted successfully with seven laboratories using solid-phase sintered silicon carbide, silicon nitride, and alumina. An objective lens with a high magnification of either 40× or 50× and a calibrated traveling stage were employed to enable both clear identification of the crack tips in high resolution and precise measurement of the crack length. Misreading of the crack length by each laboratory was reduced compared with the conventional indentation fracture method, resulting in a moderate scatter in the indentation fracture resistance (KIFR) data collected by the participating laboratories. The coefficient of variance for the three samples was less than 8%, which is comparable to those typical of standard fracture toughness tests such as the surface crack in flexure method and the single-edge V-notch method. Additionally, the results were consistent with those of our previous domestic round robin test, thus confirming the reliability of the improved IF method both internationally and domestically.
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