13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 2.3. Specimen Figure 2 shows the shape and dimensions of the specimen that was used in this study. The specimen had a chevron notch and side grooves. The fatigue crack initiated at the tip of the chevron notch, where the stress intensity factor was high. The groove on the side of the chevron notch caused Mode II fatigue crack growth in the section with the maximum shear stress and prevented crack branching in the direction of the maximum tensile stress, which was a Mode I crack. Two crack propagations were simultaneously carried out on a single specimen. Compressive force Q was applied on the crack face with the middle jigs to avoid crack branching in Mode I. In order to reduce the unexpected horizontal force applied to the specimen, three of the four grooves on the end of the cantilever were made flat and one was made larger with a radius of 1 mm to 4 mm. The three flat grooves allowed for the relative displacement caused by the elastic deformation between the specimen and the jigs. The large circular groove prevented the specimen from moving. 2.4. Experimental setup Figure 3 shows the setup of the experiment. Four ceramic cylinders were placed between the cantilevers and the loading jigs. As a result, the load applied to the specimen was divided into two equal halves on the cantilevers. A cyclic tensile load P in the form of a sine wave, ranging from 0.5 kN to 10 kN (stress ratio: R = 0.05) was applied to the center holes in the jig and specimen through two pins using a servo-hydraulic fatigue testing machine operating at a frequency of 6 Hz. In order Table 1. Chemical composition of specimen (mass %) C Si Mn P S Fe 0.11 0.27 0.55 0.021 0.023 Bal. Figure 2. Shape and dimensions of specimen (unit: mm) Figure 3. Experimental setup
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