2 Characterization of High Frequency Pulse Loading on Fatigue of Metals 13 Fig. 2.8 Strain field evolution, block 2C at HF of 35 Hz, and peak amplitude of 2600 N Fig. 2.9 Wheeler and Willenborg models pulse, a high strain hardening region is developed ahead of the crack, acting like a hard inclusion. The DIC data show how strains changed from 42 K cycles to 52 K cycles, including its size and dimensions; it includes utilization of work by Bruck [16], and modification work by Yates was utilized to locate the crack tip location [17] and associated plastic zone [18, 19]. The DIC data capture a kinking of the crack, also observed in microscope measurements, and how it circumvents around this are of high strain in order to continue its growth. This highlighted future work needed in investigating the strain fields ahead of the crack and shear effects to better understand the kinking behavior. This all leads to gaining a deeper understanding of the behavior observed by Laseure [7]. At the core of this work are the models by heeler [4] and Willenborg [5]. These models look at the plastic zone behavior, Wheeler relies on crack growth rates, and Willenborg utilizes stress intensity for the calculation, as shown in (Fig. 2.9): More recent research work by Mehrzadi and Taheri [6] and Chen [19] outline the behavior of the plastic zone ahead of the crack tip. The common thread of all these models is that an overload plastic zone is created once an overload/underload occurs, and the magnitude of this region has an effect on the crack growth rate as long as the cyclic plastic zone stays within its boundaries. The radii of the plastic and overload zone can be calculated utilizing the Irwin approximation [20]. The
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