Abstract
The effects of a surface-layer whose Young's modulus is lower than that of the substrate on the fatigue strength were studied. Pure iron plates possessing pure titanium layers on the both sides were prepared as a model material. The formation of the titanium layer remarkably improved the fatigue strength of pure iron. In addition to the fatigue test, we made a calculation of the image stress which acts on a dislocation due to the discontinuity of the elastic constants at the surface and interface. As a result, it was found that the absolute value of image stress in the vicinity of the surface becomes smaller as the elastic modulus of the surface-layer is decreased. From the results of the above experiment and calculation, it was thought that the improvement of the fatigue strength with the formation of the titanium layer was caused by the reduction in the remote applied stress and image stress acting on dislocations near the surface.
