ULTRASONIC FATIGUE TESTS ON AISI-SAE 4140 STEEL: EFFECT OF ARTIFICIAL PITTING HOLES WITH HEMISPHERICAL SHAPE ON FATIGUE ENDURANCE

摘要

This work deals with ultrasonic fatigue tests carried out on the AISI-SAE 4140 steel without pitting and with artificial pitting holes of hemispherical shape. Numerical simulation were carried out in order to evaluate the stress concentration factors in the case of artificial pitting holes;;the results show that the stress concentration factors increase considerably with the presence of artificial pitting holes and induce an important reduction on the experimental fatigue life of tested specimens. Numerical results were obtained for one and two close hemispherical pitting holes; for one pitting hole placed on a curve surface the stress concentration factor was Kt ≈ 1.7, lower than the same pitting hole placed on a flat surface: Kt ≈.2.07 Concerning the two close pitting holes, the stress concentration factor increases exponentially with the proximity of the holes;;this induces a high stress surpassing the elastic limit of testing material when a closer distance between the two pitting holes is reached. Experimental and numerical results are discussed and conclusions are presented concerning: ultrasonic fatigue life, artificial pitting holes and stress concentration factors.