DISCUSSION ON THE MASS EFFECT OF REBOUND HARDNESS THROUGH THE DEVELOPMENT OF THE SMALL BALL REBOUND HARDNESS TESTING MACHINE

Takashi Yamamoto, Kensuke Miyahara, Masayuki Yamamoto, Seijiro Maki

Abstract

Rebound hardness is a popular onsite testing method to evaluate the hardness of heavy and massive metal parts and products. However, such rebound testers are sometimes wrongly applied to small specimens that do not have enough mass. In such a case, impact energy is partly “leaked” through the vibration of the specimen and this leads to a lowered and wrong value of the coefficient of restitution. This phenomenon is called a “mass effect” and it is mainly caused by a heavy impact body mounted with a diamond or cemented carbide tip indenter.<BR />In 1987, Nakamura and Maki et al. developed a new rebound hardness tester to avoid the mass effect by using a small steel ball without an additional impact body. However, the testing direction is limited to upward only because launching a small ball in any direction was not easy at that time.<BR />In this paper, a prototype of a small ball rebound hardness tester(HNM-2012) in any direction was developed and the mass effect investigated and compared with conventional testers, using JIS Shore hardness standard blocks (&#x00D8;64×t15mm, 380 g). The advantage of a small ball rebound hardness tester is confirmed because no mass effect was observed for the tester, whereas conventional rebound testers showed a significant mass effect.

Keywords

Rebound hardness, Shore hardness, Leeb hardness, Mass effect, hardness standard blocks

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DOI

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IMEKO TC

TC5 - Hardness Measurement

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