PSI - Issue 77

L.A.S. Maia et al. / Procedia Structural Integrity 77 (2026) 87–94 Maia et al. / Structural Integrity Procedia 00 (2026) 000–000

93 7

3.4. Adhesive fillet effect With the introduction of the adhesive fillet, the length of the adhesive layer increases with decreasing θ . τ avg was calculated using τ xy only between the adherends, which is delimited by x / L O =0 and 1 in the following figures. 3.4.1. Stresses For the DP8005+AV138 joint (Fig. 8 a), peak τ xy / τ avg decreased for smaller θ . The decrease in τ xy stresses was noticeable, especially at x / L O =0.0; 1.0, where the fillet redistributed loads. By contrast, the RTV106+AV138 joint showed no improvements due to the low stiffness of RTV106. The adhesive fillet improved τ xy stresses for the DP8005+XNR6852E-2 joint. This improvement was mostly verified in the region where the adherends’ ends meet the adhesive fillet ( x / L O =0.0; 1.0), confirming that, when paired with a sufficiently robust adhesive, the fillet geometry can significantly mitigate stress concentrations at the overlap ends. σ y / τ avg stresses for the DP8005+AV138 joint are presented in Fig. 8 (b). Filleting visibly alleviated peak σ y stress concentrations of the joint. The lowest θ presented the best performance, due to a smoother transition between the adherends and the adhesives. In contrast, the RTV106+AV138 joints exhibit virtually identical σ y stress profiles regardless of the fillet presence. Peak σ y stresses remain located at the overlap ends, just as in the model without fillets. σ y stresses of the DP8005+XNR6852E-2 joints benefited from the adhesive fillet. The models with the lowest θ induced a smoother peel stress gradient, significantly reducing peak σ y stresses at the overlap edges in comparison to the model without fillets.

2

4

3

1

2

σ y / τ avg

τ xy / τ avg

1

0

0

-1

-1

-0.6

-0.1

0.4

0.9

1.4

-0.6

-0.1

0.4

0.9

1.4

x / L O

x / L O

a)

b)

7,5º

15º

30º

45º

60º

90º

7,5º

15º

30º

45º

60º

90º

Fig. 8. Normalized τ xy (a) and σ y (b) stresses for the DP8005+AV138 joint (adhesive fillet effect).

3.4.2. Joint strength Fig. 9 (a) presents the P - δ curves for the DP8005+AV138 joint. As θ decreases from 90° to 7.5°, P m significantly increases. The θ =7.5° model sustained P m =20.43 kN at δ =0.657mm (41% and 20% higher, respectively, than θ =90º. This gain reflects the more uniform stress transfer afforded by adhesive fillets. U increased as θ decreased. U for θ =7.5° was 7.14 J, which is 59.7% higher than for θ =90º. In contrast, the RTV106+AV138 joints exhibited negligible sensitivity to the adhesive fillets.

25

20

15

P m /P 90 °

P [kN]

10

5

0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

0°

15°

30°

45°

60°

75°

90°

θ

δ [mm]

a)

b)

DP8005+AV138

RTV106+AV138

DP8005+XNR6852E-2

7,5º

15º

30º

45º

60º

90º

Fig. 9. P - δ behavior of the DP8005+AV138 joint (a) and normalized P m (b) for different α .