13th International Conference on Fracture June 16–21, 2013,Beijing, China -4- 3. K expressions In situations where the linear elastic fracture mechanics theory (LEFM) is valid the crack driving force is traditionally represented by using the stress intensity factor ∆K. For the specimen type used in this investigation and for the grid constraint of our test‘s machine, the stress intensity factor for the specimen of this investigation is not tabulated in books, therefore the finite element method (FEM) was employed to obtain the value of the stress intensity factor. Figure 2 shows the K solutions used for the two configurations that have been used for test. The typical solution available in literature for SENT specimens is also shown and the difference in the given K values for a given crack length can be clearly observed. The curve was normalized by dividing the stress intensity factor by the applied stress and the crack length by the specimen length. Figure 2. Stress intensity factor obtained by finite element models for the used configurations. 4. Experimental Results 4.1. Results using the range of the stress intensity factor The fatigue crack growth rates of austenitic stainless steel 301LN at room temperature, at 3 different load ratios and different load levels are shown in Fig. 3(a). For all test conditions the crack growth rate increases with increase in ∆K. The curves show a trend that can be considered linear with positive and constant slope. The influence of load level is negligible, in spite of we found some papers that mention that some austenitic stainless materials in specimen with thin section [7,22] suffer the influence of stress level on fatigue crack growth rate. (a) (b)
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