PSI - Issue 72

P.D.A. da Silva et al. / Procedia Structural Integrity 72 (2025) 52–60

57

(a), σ y stresses for the AV138 peak at the overlap edges, and increase with L O . The increase in L O causes higher oscillation of σ y stresses in the adhesive, resulting from a higher dispersion along L O of the impact waves. σ y stress distributions for the adhesives DP8005 and XNR6852 E-2 show the same behaviour as the AV138. For the DP8005, compared to L O =10 mm, peak σ y stresses for are around 30% higher for L O =20 mm, and 104% for L O =40 mm. For the XNR6852 E-2, these values are 39% for L O =20 mm and 136% for L O =40 mm. Fig. 6 (b) shows τ xy stress curves along L O for the AV138. Equally to σ y stresses, τ xy stresses peak at the overlap edges. Peak τ xy stresses also increase with L O . For the DP8005 and XNR6852 E-2, and as happened with the AV138, τ xy stresses peak at the overlap edges, with no major difference, either in curve shape or value, for L O =10 mm and 20 mm, although there is a higher variation for L O =40 mm. Compared to the AV138, peak τ xy stresses are lower for all L O tested with the DP8005 and XNR6852 E-2, due to their lower stiffness.

6

5

4

4

3

2

 xy /  avg

 y /  avg

2

0

1

-2

0

0

0.2

0.4

0.6

0.8

1

0

0.2

0.4

0.6

0.8

1

x / L O 10 mm 20 mm 40 mm

x / L O 10 mm 20 mm 40 mm

a)

b)

Fig. 6.  y (a) and  xy (b) stresses at the adhesive layer midline vs. L O .

Fig. 7 (a) shows the P -  curves for the joints bonded with the AV138 and L O =20 mm. Between adhesives, the AV138 has the highest P m , followed by the XNR6852 E-2 and finally the DP8005. The maximum (or failure)  was inversely proportional to the adhesives’ stiffness. The P m evolution with L O is shown in Fig. 7 (b). Considering the AV138 results, P m increases with L O , but  y and τ xy stress concentrations increase as well, which results in a non proportional P m - L O relation. For L O =40 mm, due to the larger bonded length, there was plasticization of the inner adherend by around 0.3%. The tensile impact behaviour for the DP8005 showed smaller P m , without the existence of a linear trend (up to -22.8% for L O =40 mm). The XNR6852 E-2 led to the smallest P m between tested adhesives, but P m increased linearly with L O . Compared to the other adhesives, the P m reductions reached -6.7% for the AV138 ( L O =40 mm) and -24.9% for the DP8005 ( L O =20 mm).

100 120 140

80

60

0 20 40 60 80

40

P m [kN]

P [kN]

20

0

5

10 15 20 25 30 35 40

0

0.1

0.2

0.3

0.4

0.5

L O [mm] AV138 DP8005 XNR6852 E-2

 [mm] AV138 DP8005 XNR6852 E-2

a)

b)

Fig. 7. P -  curves for the joints bonded with the AV138 and L O =20 mm (a) and evolution of P m with L O for the three adhesives (b).

E a was measured by the area under the P -  curves for all joint configurations, and the obtained results are presented in Table 3. E a showed a marked increase with L O for all adhesives. The highest E a improvement over