A simple theory of rebound hardness by a spherical indenter. The influence of the conditions of a spherical indenter and a specimen on rebound hardness.

Abstract

Because the theories of rebound hardness suggested until now are based on Meyer's Law which expresses the fully plastic deformation of a specimen under a spherical indenter, the experimental results of impact carried out over a wide range conditions of specimens and indenters can't be explained by it fully and quantitatively. To solve the above points, first the simple theory of rebound hardness is obtained on the basis of three points ; (1) The relative equations of a specimen and a spherical indenter in the elastic-plastic transient indenting process (at the 1st report) are used. (2) To correspond to the various profile of indenters (D type Shore hammer, etc.), the relative equations of rebound energy including the elastic effect of the holding shaft on an indenting sphere (at the 3rd report) are used. (3) The dynamic work necessary to produce a unit volume of the permanent indentation is different quantitatively from the dynamic mean contact pressure. Secondly, the impact experiments are given by the two tip ball type indenters for several specimens, and the necessary expressions are formulated to calculate the concrete values of rebound hardness number. Finally, the experimental results by IIZUKA regarding the influence of the wide conditions of D type Shore hammer on rebound hardness number are quoted and compared with the calculated values using this theory and a good coincidence is obtained between them quantitatively in all points.