PSI - Issue 42

Jakub Šedek et al. / Procedia Structural Integrity 42 (2022) 398–403 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

400

3

Two variants of the panel were analysed – the first in pristine state (no damage or flaw), and the second with a damage presence. The damage was included in the form of initial delamination of 70 mm in length between the centre stringer and the skin.

Table 1. Composite stacking sequence of the sub-parts. Sub-part Number of plies (-)

Thickness (mm) Stacking sequence

Skin Web Cap

18 18 20

2.52 2.52

[45/-45/0/45/90/-45/45/0/-45] s

[45/90/-45/0/45/0/-45/0/45/-45/0/-45/0/45/0/-45/90/45]

2.8

[45/90/-45/0/45/0/-45/0/0/90] s

3. Test The aim of the test was the evaluation of buckling modes, stress-strain redistribution, and deformation development under continuous compression loading and strength characterization of the pristine and cracked panels. The hydraulic loading frame with a static capacity of 1.2 MN was utilized. Both ends of each panel were bonded into metallic potting plates (dimensions of 750 mm x 150 mm x 40 mm) in order to apply regular boundary conditions in the way that rotation of the test bench during mechanical loading was restricted. Only deformation in the loading direction (parallelly with stringers) was allowed. No anti-buckling device during mechanical loading was used. Panels were loaded quasi-statically with displacement control and the rate of the cross-head of 0.5 mm/min. The load-displacement curves determined by digital image correlation (DIC) are shown in Fig. 2. These data were used as the basis for correlation with simulations by means of finite elements.

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Fig. 2. Load-displacement curves determined by DIC.

The load-displacement curves were almost the same for both panels. The change of the stiffness can be seen at the compressive load of approx. 180 kN, when the buckling of the skin appeared. Both panels were able to carry the load also after buckling. The rupture of the pristine panel occurred at the load of 456 kN and cracked panel withstood the load of 476 kN. The collapse of both panels was initiated by debonding of the central stringer from the skin followed by its failure and debonding of other stringers connected with their decomposition down to sub-parts; i.e, webs and caps. Finally, total separation of sub-parts occurred together with their failures. 4. Numerical analysis The numerical analysis was utilized to predict the buckling load and the compressive strength of the pristine and cracked panels. Material parameters stated in Table 2 were used in the analysis.