PSI - Issue 64

Maciej Kulpa et al. / Procedia Structural Integrity 64 (2024) 1339–1346 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Exemplary strain results During the test load, simultaneous DFOS measurements were performed on all measurement routes. Examples of the strain plots caused by the maximum load in scheme S1 and measured with sensors placed in the lower laminate are shown in Fig. 8.

0

L3 L4 L5 L6 L7 L8 L9 L11

40

80 Strain [10 -6 ] 120

160

200

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Panel's length [m]

Fig. 8. Strains measured by all DFOS sensors installed in the lower laminate under maximum load in scheme S1

It can be seen from Fig. 8 that the load distribution throughout the length of the panel was quite even, with a slight (approx. 20%) increase near the panel axis (sensor L6). The maximum recorded strain of 183× 10 -6 corresponds to only 6 MPa (Young modulus of the lower laminate is 35 GPa), which confirms that in this type of structures the ultimate limit state is not crucial and does not govern the design stage of the structure. However, a local peak can be observed in strain plots recorded by sensors L4, L7, and L11. These are not very dangerous at the moment because no local point achieved strain values greater than in the mid-span of the panel, but they are places that require further attention. These peaks may occur as a result of local imperfections in the laminates or the sensor itself, which may be bent as a result of high pressure during manufacturing. The latter effect is more likely due to the low material stress, and practically no permanent strains were observed after unloading the panel. However, these places have been precisely inventoried and will be subjected to detailed observation during planned subsequent field loads and observation using non-destructive diagnostics of composites by ultrasound.

-250 -200 -150 -100 -50 0 50 Strain [10 -6 ]

U6 - I U6 - II U6 - III U6 - IV U6 - V U6 - VI L6 - I L6 - II L6 - III L6 - IV L6 - V L6 - VI

100 150 200

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Panel's length [m]

Fig. 9. Strains measured by sensors U6 and L6 in subsequent stages of loading in the S1 scheme