Effect of Presence or Absence of a Screw for Fixing Specimen on Rebound Hardness Test by Using Hammer with Vickers Indenter

For manufacturers, rapid and accurate quality control of materials and products in the field is essential for improving competitiveness. Rebound hardness testing is one of the fundamental material tests expected to meet this requirement. However, it has been known that many factors affect rebound hardness which may cause the fluctuation in the measured value. In order to elucidate the effect of the fixing method of the specimen, the coefficient of restitution of a hammer using a Vickers indenter was compared with and without bolting the specimen to the base. The motions of the hammer and the specimen were measured simultaneously using two laser Doppler vibrometers and were also numerically analyzed using an elastoplastic finite element method. It has been clarified that, in the case of without bolting, the restitution coefficient is decreased compared to with bolting. The decreasing tendency becomes larger as the impact point moves away from the specimen center. The rebounding behaviors of the hammer and the specimen without bolting can be reproduced with a numerical model in which an appropriate elastic film is inserted between the specimen and the base. The numerical results show that the hammer impact causes rigid body motion in the specimen, which consumes hammer energy, resulting in a decrease in the coefficient of restitution. The range in which the coefficient of restitution can change is also evaluated by assuming a simple two-body collision model.