PSI - Issue 13

Valentin Tkachenko et al. / Procedia Structural Integrity 13 (2018) 1396–1401 Author name / Structural Integrity Procedia 00 (2018) 000–000

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(a) (b) Fig. 1.The geometry of crack growth specimen (a) and its model for numerical simulations (b).

Results

The result of fatigue crack growth under ultrasonic loading is presented on the kinematic diagram in fig.2. The diagram has a clear knee point at the threshold value. On the right side from this threshold value the kinematic diagram has a linear law in log-log coordinates.

Fig. 2. Kinematic diagram of fatigue crack growth under ultrasonic loading.

The trend line of these results was determined by least square method and the power was found out for it. These results are in good agreement with well known Paris law of crack growth. The experimental data were used to establish the relation between acting SIF and crack growth rate that further was used in mathematical model of curvilinear crack growth. These results were obtained for cracks with a straight crack front, fig.3-a. However, sometimes the crack initiation site is shifted to one of a lateral surface of the specimen, fig. 3-b. In this case the shape of crack front develops in curvilinear mode. Clear crack arrest marks were observed on the fracture surface, fig.3-b. Mathematical model to predict the shape of curvilinear crack was build based on the results of crack growth tests, fig. 2 and SEM observations. The initial crack front shape for mathematical modeling was build based on the first crack arrest mark at fracture pattern, fig. 3-b. After, this envelope line was used in numerical 3D simulation to confine the free surface (crack).