INVESTIGATION OF THE RESPONSE OF DUAL-PHASE STEELS SUBMITTED TO 20 KHZ AND LOW FREQUENCY FATIGUE LOADINGS

摘要

Application of piezoelectric fatigue systems working at ultrasonic frequencies has enabled efficient testing in the desired Very-High-Cycle (VHC) ranges. However, the controversy is over whether the high- loading frequency affects the fatigue response of the materials or not. In this work a ferritic-martensitic dual-phase steel was investigated under ultrasonic 20 kHz loading as well as conventional low frequency fatigue tests. The objective was to study the possible effect of frequency on high and very-high-cycle fatigue behavior, thermal response of the material as well as the deformation and fracture mechanisms. The S-N curves were obtained and compared for 20 kHz and 30 Hz cycling. In addition, fractography studies were conducted to reveal the crack initiation and fracture mechanisms for ultrasonic and conventional fatigue loadings.