Thermal radiation of steel specimens under cyclic loading

Abstract

1. The obtained formulas of mathematical approximation of the experimental dependences of the heating of material on stress make it possible to determine unambiguously the fatigue limit of medium carbon steels under cyclic circular bending by a nondestructive method. 2. The regularity of the change of intensity of the energy flux with increasing load can be detemiined in operation at each stage within a mere 15–20 sec. With such a test regime the tests can be considerably shortened, and the noise due to heating of the headstock and tailstock of the machine can be reduced. 3. To determine the energy characteristics of a material in the process of stepped loading, the results obtained after the third loading block have to be used because in the course of the preceding blocks the material loses strength and it adapts to the loads. 4. In nonsteady loading regime the thermal characteristics are affected by the history of the loading; the power of the thermal radiation has a tendency toward stabilization of decrease after recovery of the metal, and it increases when the level of the preliminary loads increases. 5. Technological factors (surface treatment and coating) change the thermal characteristics and correspondingly the fatigue limit of specimens.