Effect of Impact Angle on Rebound Hardness and Their Correction.

Abstract

A method of rebound hardness testing is introduced in which a hammer propelled by a spring mechanism strikes a sample surface. The rebound hardness is obtained by dividing the rebound velocity of the hammer by its impact velocity. This method can be applied for any impact angle, but the values obtained at some angles deviate from the true hardness because the velocities are affected by the component of gravity and other factors such as friction. The impact and rebound velocities at various impact angles are measured and the relations between the velocities and the angles are distussed. The hardness value is found to increase as the impact angleθ, the angle between the impact direction and gravity direcction, increases. For less hard materials, the calculated hardness is more closely dependent on θ. In addition to this, the impact and rebound velocities have a linear relation to the cosine of θ. These results determine the relation between the rebound hardness and the impact angle. That is, the hardness values can be obtained by using an impact angle derived from the impact velocity.