Abstract
It has been a general practice that the C scale of Rockwell hardness tester was widely used to measure the hardness of steel balls. But, to acquire the true hardness number of steel balls, the relation between the hardness munber measured on the spherical surface and that on the plane surface should be considered. Zhe present authors introduced two assumptions, and traced mathematically the relationship among the spherical hardness, the radius of steel balls and its correction value. The result of calculation was ΔH=29.5 (l-H/160)2/γ, which was also justified by the experimental value. Furthermore, the relation between the hardness number of steel balls gained by the Rockwell test and that by the rebounding one was shown by our experiments. In a rebounding test, the physical mechanics of the coefficient of the rebound had been little known. We, authors, presented a simple dynamic theory of the coefficient of the rebound, which might be summerized in the following expression; e=1/√l+K'K'', where K' corresponds to the coefficient of elasticity in collision, and K'' the coefficient of the permanent strain in collision. The experimental results of Rockwell tester using, concerning the coefficient of the rebound between steel balls and anvils were approximately interpreted and the coefficient of the rebound in the rebounding test was found to be nearely equal to the calculated value.
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