CURRENT STATUS OF REBOUND HARDNESS TEST BLOCKS IN JAPAN AND OUTLOOK

摘要

Currently, about 30,000 high-precision, standardized hardness blocks are supplied to the Japanese market each year, and are available in about 140 different types. The history of hardness blocks in Japan can be traced back more than 70 years to the development of the Shore hardness block (cp64xt 15 mm) by Shoichi Yamamoto. In Japan, the Shore block has the largest share of the market for rebound hardness test blocks. Recently, however, the Leeb hardness block has also been increasingly used for rebound hardness testing, and the R type ((pll5xt 33 mm) and P type (cp90xt 56 mm) Leeb hardness blocks are produced exclusively in Japan. The successful expansion of the Shore hardness test in Japan is due to the use of Vickers hardness values, which are more reliable than Shore values, and the VHS conversion method adopted by the Japan Industrial Standards (JIS). This paper discusses how differences in geometry between the R- and P-type Leeb hardness blocks influence Leeb hardness values. Based on hardness measurements using the Vickers and Leeb (HLD and HLE) hardness scales with these Leeb blocks, a method for converting Vickers hardness values into Leeb values is also discussed. As a result, no influence from geometric differences on the Leeb (HLD and HLE) hardness measurements is found, and conversion from Vickers to Leeb hardness can be defined by the same formula for both R- and P-type blocks.