PSI - Issue 24

Vito Dattoma et al. / Procedia Structural Integrity 24 (2019) 978–987 Dattoma et al. / Structural Integrity Procedia 00 (2019) 000 – 000

980

3

specimens are reported. Experimental overview of fatigue bending tests shows general data variation in damage modes due to test variability, but after tests, even that different fatigue failure zones of specimens are evaluated, good coherence of resulting life is observed. In Figure 1b, diagram illustrates resulting trend of maximum test load as function of fatigue c ycles’ number, where linear behavior is approximately identified in double logarithmic plot.

Table 1. Mechanical/ physical properties of CFRP material constituents.

Property E 11 (GPa) E 22 (GPa) E 33 (GPa) G 12 (GPa) G 23 (GPa)

Fiber

Matrix

Laminae 128.638

290

3.4 3.4

14

7.336 7.336 4.045 2.912

/

/

25

1.25 1.25 179 0.43 0.43 1.24

7

/

T g (°C)

/

0.236 0.011 1.785

ν 12 ν 23

0.34

0.545

ρ (g/cm 3 )

/

(a) (b) Fig. 1. (a) Schematic view of four-point bending test ASTM D7264M – 07; (b) fatigue curve diagram.

Table 2. Scheduled experimental results for each fatigue bending tests.

ID P1 P2 P3 P4 P5 P6 P7 P8 P9

F max_norm [%]

F Amp_norm [%]

N. cycles (N f )

Damage zone and type

58.30 53.39 52.76 49.96 58.96 54.98 47.81 51.39 52.59 60.56

27.70 25.34 24.07 22.87 28.68 26.29 22.07 23.74 23.90 29.48

71798 78316 204000 142677 18930 25800 442561 185343 73696 13289

Crack at upper left support and delamination in 6° and 16° layers;

Delamination in 5° and 16° layers Delamination in 6° and 24° layers

Crack on 1° ply; delamination in 2°, 16° and 30° layers

Delamination in 10° layer Delamination in 10° layer

Undamage

Delamination in 6° and 8° layer Delamination in 6° and 10° layers

P10

Delamination in 10° layer

3. Damage monitoring methods and numerical model 3.1. Thermographic control

Thermographic controls are performed using a cooled IR camera FLIR X6540sc (Flir System, Inc. Winstonville, OR, USA) with 640×512 pixels. Thermal sequence is acquired with a sample rate of 117 Hz, with an observation time of 10 seconds. It is important to highlight as 117 Hz represents the maximum value of the sample rate selectable from IR camera to acquire frames of whole specimen. An optimum set-up arrangement is proposed as in Fig. 2b, where