PROOF EXAMINATION ON SMALL REBOUND HARDNESS CARRIED OUT WITH HLD/HLE STANDARD BLOCKS

摘要

Conventional rebound hardness tests like Shore and Leeb hardness tests are mainly applied for massive and large specimens like mill roll. For small or thin specimens, however, "mass effect," i.e., loss of impact energy due to vibration of specimens during impact cannot be ignored. Nakamura and Maki proposed a simple rebound hardness test using a small ball indenter that is expected to reduce the mass effect. In this paper, we developed a prototype of a free-fall-type rebound hardness tester and carried out experiments to provide fundamental information necessary to establish Nakamura-Maki method industrially. Impact velocity and rebound velocity of ball indenters are estimated from free-fall height and rebound height, respectively. Experimental parameters are impact velocity, size, and materials of ball indenters. The most important result obtained is that coefficient of restitution, i.e., rebound hardness, is almost independent of the size of ball indenters and the rebound hardness scale can be set once other experimental parameters were fixed. Further study will be necessary to optimize experimental conditions and to measure accurate impact and rebound velocities in order to realize a versatile tester based on Nakamura-Maki method.