Abstract
Welded parts fabricated from high-strength steel (HSS) require an almost infinite lifetime, i.e., a gigacycle (109). Therefore, it is necessary to test its high-cycle fatigue behavior. In this paper, an accelerated fatigue test method using ultrasonic resonance is proposed. This method reduces the experimental time required in comparison with a conventional fatigue test setup. The operating principle of the accelerated ultrasonic fatigue test involved the use of a 20-kHz resonant frequency. Therefore, it was necessary to design a specimen specifically for the test setup. In the study, ultrasonic fatigue testing equipment was used to test butt-welded 590- and 780-MPa ferrite–bainite steel plates. In order to design the specimen, a dynamic Young’s modulus was measured using piezoelectric element, a laser Doppler vibrometer, and a digital signal analyzer. The S–N curves of fatigue behavior of the original and butt-welded specimens were compared. The fatigue test results showed that the infinite (i.e., gigacycle) fatigue strengths of the welded specimens were approximately 8% less than those of the original specimen.
Highlights
The fatigue test results showed that the infinite fatigue strengths of the welded specimens were approximately 8% less than those of the original specimen
Industrial development has led to increasing demand for parts and elements with a longer service life
Previous studies determined that differences exist between fatigue and fracture behaviors according to the test regime
Summary
Industrial development has led to increasing demand for parts and elements with a longer service life. Previous studies investigated gigacycle fatigue regimes to assess fatigue behavior in applications in the aerospace, space, high-speed rail, automotive, and biomedical industries. These applications involve operation under severe environments and in situations where it is difficult or impossible to replace parts. The maximum load was applied at the center of the specimen, and the maximum displacement was observed at the free end For this ultrasonic fatigue test, the design of the test specimen was critical because it was necessary for the Metals 2017, 7, 103; doi:10.3390/met7030103 www.mdpi.com/journal/metals. Most previous studies were performed with hourglass-type solid cylindrical specimen to resonate.
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