PSI - Issue 52

Ruben I. Erives et al. / Procedia Structural Integrity 52 (2024) 600–610 Ruben Erives et al./ Structural Integrity Procedia 00 (2019) 000–000

607

8

60

95% confidence intervals

40

20

0

0

20

40

60

80

Fig. 6. Deviation from linearity as a function of the measured phase angle

4.3. The delamination onset parameters The initiation of fracture resistance, 0 , was determined by reading the value of the fracture resistance at delamination onset (measured from AE signals). Similarly, the initiation end-opening, 0 , is correlated to the onset time, 0 . In Fig. 7, two plots are shown with a) the end-opening displacement as a function of time, and b) The fracture resistance versus displacement curve with the initiation marked with a solid vertical black line.

10 4

10 5

1

15

5000

4

0.8

4000

3

10

0.6

Delamination onset

3000

2

0.4

2000

Delamination onset

5

1

0.2

1000

0

0

0

0

50

100 150 200 250 300

0

0.5

1

a)

b)

Fig. 7. a) End-opening displacements and cumulative energy as a function of time, and b) R-curve with the cumulative energy as a function of the end-opening The delamination onset parameters, i.e., 0 , 0 , from all tests are shown in Fig. 7a and 7b respectively. The blue markers correspond to the parameters obtained with AE, while the red markers correspond to the parameters obtained using the deviation from linearity. It can be noted that both criteria show very similar parameters, and excellent correlation. The initiation end-openings are plotted using the log( 0 ) since the values are very small. Furthermore, using the log of the value provides a better fit.