Suppression of Measurement Variability in Rebound Hardness Test Using Hammer with Vickers Indenter: Roles of Hammer Mass and Impact Speed for Insufficiently Fixed Specimens

For manufacturers, rapid and reliable hardness testing of metallic components in the field is essential for ensuring quality and competitiveness. Rebound hardness testing using a hammer with a Vickers indenter has been proposed as a method that minimizes dependency on impact velocity. However, the reliability of this method can be affected by specimen fixation conditions. In this study, the influence of hammer mass and impact velocity on the coefficient of restitution was investigated using two types of hammers with different masses. Experiments were conducted on specimens with varying surface roughness under both fixed and non-fixed conditions. The motions of the hammer and the specimen were measured simultaneously using two laser Doppler vibrometers. Results showed that when the specimen is not bolted, part of the hammer’s kinetic energy is transferred to the specimen’s rigid body motion, leading to a decrease in the coefficient of restitution. This effect was more pronounced with heavier hammers and increased impact distance from the specimen center. Conversely, lighter hammers reduced the specimen’s motion energy more effectively, thereby suppressing the decrease in restitution. Additionally, changes in impact velocity did not significantly affect the restitution coefficient for a given hammer mass. These findings suggest that hammer mass plays a more critical role than impact velocity in determining the required specimen mass under insufficient fixation conditions, and validate the applicability of a predictive model for estimating apparent restitution coefficients.