The purpose of this paper was to make clear the effect of specimen dimension on surface damage under an action of pulsating impact contact load. The dynamic stress produced by a falling weight on a rod specimen was studied at first, and the dynamic strain was measured. In pulsating impact experiments, two series of commercial steel S25C and S45C were used. The surface damage was defined by the first appearance of a pitting on the surface and the pulsating number Np till to the appearance was discussed. The results obtained are summarized as follows.
(1) A concise equation for the dynamic stress in a rod specimen produced by a falling weight was formulated.
(2) The dynamic strain showed a good correspondence to the theoretical result and the distribution of the maximum shearing strain was given.
(3) The surface hardness HV increased with an increase of number of impact. But no clear correlation was found between HV and Np.
(4) Np was smaller for a shorter length specimen and larger for S45C than S25C. The increase of surface hardness by heat treatment caused an increase in Np.
(5) Before an appearance of a pitting, several visible cracks were seen on the surface of a specimen.
These results were explained by taking into account the effect of the superposition of stress waves, which were produced by an impact load, in a specimen. The effect depended on the dimension of a specimen.
