PSI - Issue 13

A.A. Lukyanchuk et al. / Procedia Structural Integrity 13 (2018) 1285–1290 A.A. Lukyanchuk and others / Structural Integrity Procedia 00 (2018) 000 – 000

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Figure 6 - : Specimens No.151, 157 after reaching the thickening of 0.05 mm

Figure 7 shows a photo of two specimens after an ultrasound inspection with the noted typical fatigue damage. Specimens are shown after reaching: a thickening of 0.05 mm and runtime of about 50 000 cycles; achieving a thickening of 0.1 mm and runtime of about 1 000 000 cycles.

(A). (B) Figure 7 - A) Specimens No.149 and 151 after reaching a thickening of 0.05mm; B) Specimens No.149 and 151 after reaching a thickening of 0.1mm

4. Results of fatigue tensile tests using the proposed failure criterion

To check the results (sensor designed and criteria) additional fatigue tests of that kind of specimens were carried out. The main interest was the possibility of derivation S-N curve from the data obtained for further estimation of fatigue. Specimens were tested under regular loading with the stress ratio: R = 0. The tests were carried out at three loading levels. The loading levels were chosen to obtain the fatigue lives in the required range. The delamination occurred in the range of 10 3 ÷ 10 6 cycles. Complete destruction according to the "classical criterion" was not achieved by any single specimen. The values of the fatigue life were recorded only by the delamination sensor in the zone of the hole, criterion (1) was used for this. When criterial value was reached, the specimen was considered to be failed. The results of the inspection of specimens by ultrasonic methods corresponded to the data described in the section above. The results of fatigue tensile tests of open-hole specimens are shown in Figure 8. It also shows the S-N curve approximated. Fatigue scattering parameter S lg N is 0.21. The experimental data for the construction of the S-N curve were approximated by a power law in the form [6, 7]:       lg lg , , lg R m с R R с N C m N C m            (2)

    

R m – experimental constants; N и  – fatigue and maximum stresses of regular loading.

where C и