PSI - Issue 68

Gül Demirer et al. / Procedia Structural Integrity 68 (2025) 190–196

195

6

G. Demirer and A. Kayran / Procedia Structural Integrity 00 (2024) 000–000

Fig. 4. Buckling mode shapes of the baseline laminate and optimized VS laminate; U3 denotes the out-of-plane displacement.

Panel with gaps

Panel with overlaps

Pixelation, 160 elm. Pixelation, 640 elm. Pixelation, 1440 elm. Defect Layer, 160 elm. Defect Layer, 640 elm. Defect Layer, 1440 elm.

40

40

30

30

20

20

Pixelation, 160 elm. Pixelation, 640 elm. Pixelation, 1440 elm. Defect Layer, 160 elm. Defect Layer, 640 elm. Defect Layer, 1440 elm.

Load [kN]

Load [kN]

10

10

0

0

0

0.5

1

1.5

0

0.5

1

1.5

Displacement [mm]

Displacement [mm]

Fig. 5. Load-displacement curves indicating mesh dependency of pixelation and defect layer methods

Table 1 presents the results visualized in Fig. 6, normalized with respect to the reference isotropic case. The VS design demonstrates a 59% higher buckling load compared to the straight fiber laminate when defects are not considered. This improvement in buckling load, however, comes with a reduction in sti ff ness, as the optimization focuses on maximizing buckling load without constraints on sti ff ness. The sti ff ness values tabulated in Table 1 are calculated from the slope of the linear portion of the load-displacement curves. When a 0% coverage manufacturing strategy is employed, gaps emerge, resulting in a 6.9% and 13.6% reduction in expected buckling load and in-plane sti ff ness, respectively. Despite the weakening e ff ects of gaps, the defective VS laminate still outperforms the baseline in terms of buckling load. Conversely, with the 100% coverage strategy, overlaps lead to further improvements of 29.6% in buckling load and 5.1% in in-plane sti ff ness. Although 100% coverage strategy seems advantageous, it is important to note that overlaps introduce thickness non-uniformity and weight penalty.

Table 1. Change in normalized buckling load and in-plane sti ff ness after incorporating gaps and overlaps by defect layer method (640 elements).

Laminate

Normalized Buckling Load

Normalized Sti ff ness

Value

Change (%)

Value

Change (%)

Ignoring defects

1.59 1.48 2.06

-

0.59 0.51 0.62

-

With gaps (0% coverage)

-6.92%

-13.56% + 5.08%

With overlaps (100% coverage)

+ 29.56%