PSI - Issue 42

V. Shlyannikov et al. / Procedia Structural Integrity 42 (2022) 714–721 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The test setup included a Zwick/Roell HA100 servo-hydraulic test frame with a Zwick CUBAS control system. The mixed mode cyclic fracture tests were performed at a load ratio R = 0.1 with discrete applied force direction. A S-shape grips (Richard et al. (1983)) are utilised to deliver mode mixity between pure mode I and pure mode II loading conditions (Fig. 2). Pure Mode I is obtained when the force F is applied in a β = 90◦ direction, whereas pure mode II is achieved by applying the force F in a β = 0◦ direction. The CTS specimens mode I and mode II loading conditions are listed in Table 2. An optical microscope is used to determine the actual position of the crack tip on the curvilinear crack path monitoring (Fig. 2a), and continuous measurements of the crack size are made along the path in the CTS specimen. As a result of the tests, experimental crack paths were obtained based on periodically measured increments of crack length in mode I and initial mode II loaded CTS specimens for all the materials we are considering (Fig. 3).

Fig. 2. Test equipment. (a) Mode I; (b) Mode II.

Also in this study, the displacement and strain fields around of the crack tip in the CTS specimen were measured using digital image correlation (Fig. 2b). The images were captured using an Isi-sys 3D-Micro-DIC stereo sensor system. The stereo system includes high-speed video cameras CameraIQ-7H-3 with a resolution of 2448x2048 5.0 MP. The cameras are equipped with a set of lenses with a fixed focal length to provide fields of view from 100x75 mm to 200x150 mm. For the correct implementation of DIC, one of the faces of the specimens was prepared by spraying a black speckle over a white background. During mixed mode fatigue tests, the loading cycle was periodically paused to allow the acquisition of a sequence of images at uniform increments through a complete loading and unloading cycle.

Fig. 3. Experimental crack paths for the initial pure Mode II fracture.