Effect of fatigue crack propagation on natural frequencies of system in AISI 4140 steel

In this study, effect of fatigue crack growth on the natural frequency of the beam that having a great importance in engineering applications, was studied. Beams which have a very wide application areas, are often used as the basic structural member in engineering structures. Therefore, early detection of damage that may occur in these structures is of great importance for the prevention of devastating damage. In the early detection of damages, one of the most commonly used methods is the vibration analysis of the structure. Thus, the detection of the changes in the natural frequencies of structure and monitoring the natural frequencies' changes is very important. From this point, in this study, the effects of fatigue crack growth on the natural frequency of the beam that produced from 4140 steel, are investigated experimentally and numerically. The length and cross-sectional area of the beam are 500 mm and 8x16 mm2, respectively. 3 mm long and 0.25 mm wide crack was opened to the beam by using wire EDM. Then beam subjected to 3-point bending test with 10 Hz in dynamic fatigue device and measuring the natural frequency of the beam periodically changes that occurring in the natural frequency of the beam is measured. These data was used to detection and determine the size of the fatigue crack in the beginning of the crack propagation in beams that subjected to dynamic loading. Experimental data showed that the natural frequency of the beam decreases corresponds to fatigue crack growth in the beam.