Effect of test piece length on the fatigue strength of steel in air

Abstract

1. It is established that the scale factor for short fatigue test pieces is a function of their diameter, length, and shoulder radius, the latter parameter having no effect on the fatigue properties of long test pieces. 2. Our results, demonstrating the dependence of the endurance limit (the principal fatigue strength characteristic) on the length and, consequently, the volume of the test piece, lend support to the statistical theory of the scale factor, the validity of which was doubtful before the existence of such a relationship was established. 3. The results of the present investigation show that the resistance of materials to cyclic stresses should be determined on test pieces of two distinct types: either on test pieces of “zero” length (as recommended by a new draft Soviet standard) which are least affected by the scale factor (Fig. 3), or on specimens long enough to exclude the effect of the shoulder radius.