PSI - Issue 5

A. Prokhorov et al. / Procedia Structural Integrity 5 (2017) 555–561 A. Prokhorov et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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All of specimens have inclusions on the fracture surfaces having complex chemical composition, which can be the sources of fracture.

a

b

c

d

Fig. 7. Fracture surface of specimen tested with water cooling (a), the fist area of fatigue fracture (b), the second area of fatigue fracture (c) with partial fracture on the grain boundaries (red arrow), the third area of fatigue fracture (d)

5. Discussion

Fatigue tests were carried out with two different conditions: ultrasonic test with air cooling and potential drop method and ultrasonic test with water cooling. The results obtained after the first kind of test allow us to show that the signal of potential drop shows the sharp increase on the last stage of test, which we can associate with fracture areas. Also, we can associate this increase with temperature rise which has been shown in previous works Plekhov (2014). The second type of experiments illustrates the three stages of fracture evolution. Authors suppose water influence on the fracture evolution on this material because the first types of tests do not show these stages. Structure evolution can be understood using another non-destructive method or modified PDM. The qualitative different scenario of fracture under water and air cooling were observed. The fracture initiation under air cooling conditions is observed into the grain volume and has brittle character. The prolongation of fatigue life using water cooling leads to the grain boundaries fracture and failure initiation caused by disclination motion.