PSI - Issue 7

Igor Varfolomeev et al. / Procedia Structural Integrity 7 (2017) 359–367 Igor Varfolomeev et Al./ Structural Integrity Procedia 00 (2017) 000–000

361

3

Based on the above information, three bone-shaped specimens with rectangular cross-sections were manufactured from the material blocks with the specimen numbers referred to as FZ1, FZ2 and FZ3, respectively. When cutting the specimens out of the material blocks, the defects were expected to be centered in the cross-section and their principal planes corresponding to the two largest defect extensions to be oriented normal to the load direction. Table 1 provides an overview of the specimen and defect sizes as well as some details of the load blocks applied during testing. Accordingly, two load levels with the maximum tensile stress of 600 MPa or 800 MPa were applied, whereas the stress ratio was set to be = 0.1 . Except for the FZ3 test, load blocks with 600 MPa and 800 MPa, each consisting of 6,000 cycles, were alternately applied. Fatigue crack propagation was monitored by means of beach marks introduced by either temporarily increasing the stress ratio from = 0.1 to = 0.5 … 0.6 (specimens FZ2 and FZ3) or periodically applying loading blocks with different stress magnitudes (FZ1). In their test area, all specimens were additionally instrumented with clip gages in order to detect a deformation increase indicating a considerable amount of crack propagation preceding the final failure, see Fig. 2.

Block 1

Block 2

Block 3

Fig. 1. UT indications showing the defect size and distribution.

Fig. 2. Test specimen instrumented with a clip gage.

Table 1. Size of the test specimens and defect fields, as well as a summary of the test program.

Block / Specimen

Cross-section [mm × mm]

Defect size estimated from EFBH [mm]

Overall number of cycles (excluding beach marks), maximum stress 42,300 cycles: 7 alternating blocks of 600 MPa and 800 MPa, each consisting of 6,000 cycles, final block of 300 cycles with 800 MPa 33,000 cycles: mainly at 600 MPa, about 580 cycles at 800 MPa 20,000 cycles at 600 MPa followed by 19,900 cycles at 800 MPa

Change stress ratio for setting beach marks

1 / FZ1

30×20

1.3

−

2 / FZ2

52×35

2.7

●

3 / FZ3

30×20

1.6

●