PSI - Issue 47

G. Anglani et al. / Procedia Structural Integrity 47 (2023) 552–562

560

G. Anglani et al. / Structural Integrity Procedia 00 (2023) 000–000

9

Calm Ratio vs Felicity Ratio - Both Specimens

PUC Self-Repaired after fatigue

300

1400

1

Force Fracture Energy

1200

250

Heavy damage

Intermediate damage

1000

FR: 0.260537 CR: 0.596386

200

800

150

0.5

600

FR: 0.888975 CR: 0.311110

Force [N]

Calm Ratio

100

Intermediate damage

Light damage

400

50

200

Cumulated Fracture Energy [N/m]

0

0

0

0

0.05

0.1

0.15

0.2

0.25

0.3

0

0.5

1

Displacement [mm]

Felicity Ratio

(a)

(b)

Fig. 8: Damage assessment diagram for the collapsed and uncollapsed specimen (a); Load-displacement and fracture energy curves of the self repaired specimen from a static test to evaluate the resin performance after fatigue (b).

Table 1: Comparison between PUC specimens — Virgin, Self-Repaired, and Self-Repaired after 5000 loading cycles.

Specimen

Maximum Load ( N )

Fracture Energy ( N / m )

PUCVirgin

1107 880.7 836.1

275.7 240.7 231.3

PUC Self-Repaired

PUC Self-Repaired after 5000 load cycles

3.2. b-value Analysis

For the case of the collapsed specimen, the 189 AE signals recorded were divided into windows containing 15 signals each, with a step of 5 signals. The b -value was calculated according to the procedure described in section 2.3. The b -value variation during the fatigue cycles can be seen in Figure 9.

b -value evolution with N of cycles

1.6

1.4

1.2

1

0.8 b -value

0.6

0.4

b -value at collapse

0.2

500 525

550

600700721

N of cycles

Fig. 9: Evolution of the b -value with the number of cycles, until collapse.

It can be observed that the b -value accurately indicates when catastrophic failure is about to occur as, shortly before the failure, it starts to present an erratic behavior and reaches low values (0.2–0.6). As demostrated by [36], the b value is usually comprised between 1.5 and 1.0 when damage is spread over the volume of the specimen, it reaches 1.0 when the damage coalesces in the fracture surface, and it can go below 1.0 when the specimen is broken into two parts (failure). Moreover, as shown by [38], the b -value can be associated to the fractal dimension of the fracture