PSI - Issue 28

S.V. Suknev et al. / Procedia Structural Integrity 28 (2020) 903–909 Author name / Structural Integrity Procedia 00 (2019) 000–000

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5. Results Figure 2 illustrates experimental data (dots) on the critical load at the instance of the initiation of tensile cracks at the hole as a function of its diameter 2 a , obtained in the first series of tests and the results of calculating the critical pressure according to the FFM using Eq. (2) for 0   (curve 1) and 0.6   (curve 2). The stresses 1  and 2  are calculated by the finite element method at the center of the specimen with no hole, loaded via inserts of a given size. The size 0 d is determined from the best match between the calculation results and the experimental data. Its value is 1.0 mm, which is comparable with the size of the largest pores in the material. In accordance with Eq. (3), the stress s T is equal to 0 T in the first case (dashed line) and 0 1.3 T T s  in the second case (solid line).

p c / C 0

0.8

2

0.4

1

0

20 2 a , mm

0

5

10

15

Fig. 2. Critical pressure versus the hole diameter.

Figure 2 shows a significant size effect, i.e., the effect of the hole diameter on the local strength of the material. As it decreases, the critical pressure increases, reaching the ultimate compressive strength, and, as it increases, it asymptotically approaches the stress 0 1.3 T T s  . This behavior of critical pressure is well described by the modified FFM and the others TCD methods. In these methods, the length scale parameter (size of the fracture process zone) is represented in accordance with Eq. (1). Figure 3 shows experimental data (dots) on the critical stress at the instance of the initiation of tensile cracks at the hole as a function on the biaxiality ratio and the results of calculating the critical stress according to the FFM using Eq. (4). The calculations are carried out using 0 d and  , determined in the first series of tests. The dashed curve is calculated according to the traditional approach for 1   .

 c /  0

3

2

1

0

0

0.1

0.2

0.3



Fig. 3. Critical stress versus the loading biaxiality ratio.