PSI - Issue 47

Francesco Ascione et al. / Procedia Structural Integrity 47 (2023) 826–841 Author name / Structural Integrity Procedia 00 (2019) 000–000

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unstable state to stable one, the load restarts to increase). 2.2 Influence of the absorption on the fracture energy in mode II

In Table 1, the average (µ) and standard deviation (  2 ) values of the three above mentioned loads P, of both the corresponding vertical displacement δ (ENF test) and the fracture energy values, are collected. The values for the aged specimens are those relative to the end of the immersion period: 15 months for SikaDur 30 and 12 months for Araldite [Ascione et al. 2021].

Table 1. Test results relative to SLJ specimens after absorption period. End of Elastic Stage

End of Post-Elastic Stage

End of fracture propagation

P nl [N]

δ nl

G II, Pnl [N/mm]

P max [N]

δ max

G II, Pmax [N/mm]

P u

δ u

G II, Pu

[mm]

[mm]

[N]

[mm]

[N/mm]

μ

1577 0,05 1492 0,06 1622 0,01 2053 0,03 1430 0,01 892 0,15

2,56 0,01 2,33 0,04 2,82 0,01 3,30 0,03 4,05 0,11 2,60 0,13

0,38 0,14 0,31 0,16 0,39 0,03 0,59 0,10 0,59 0,10 0,23 0,38

1624 0,04 1642 0,04 1744 0,02 3129 0,10 2082 0,01 1030 0,09

2,72 0,02 2,68 0,04 3,16 0,01 5,26 0,11 7,73 0,01 3,16 0,07

0,47 0,14 0,48 0,17 0,59 0,06 1,97 0,37 1,77 0,03 0,38 0,21

1366 0,03 1385 0,14 1585 0,03 2941 0,11 1935 0,00 1060 0,01

2,57 0,02 2,87 0,04

0,58 0,11 0,69 0,13 0,81 0,08 4,11 0,34 3,28 0,00 0,92 0,03

Unaged

σ 2

μ

SikaDur30

Aged (SW),A

σ 2

μ

59,11 4,45 6,68

Aged (TW),A

σ 2

μ

Unaged

σ 2

0,11 9,18 0,00 4,44 0,01

μ

Aged (SW),A

Araldite

σ 2

μ

Aged (TW),A

σ 2

A= continuous absorption In Figure 4, all the experimental P- δ curves for the unaged and aged specimens and for both resins are depicted. Matching the values of Table 1 and the curves of Figure 4, it is possible to observe that in general no relevant changes for SikaDur30 were revealed even if an increment of the fracture energy �� , � � was recorded. This last result was due to the curing degree of 87% reached by means of a curing temperature of 23°C [Ascione et al. 2021]. The temperature of the water (30°C) in which the samples were immersed activated a post curing phase which effect is greater than the degradation due to plasticization and/or hydrolysis. In opposition, significant changes were monitored in the case of Araldite. In general, the decrease of Araldite was due to the fact that its curing degree (the curing was performed under the same conditions as SikaDur 30) was equal to 98%. The temperature of the water, differently from the case of SikaDur 30, was not sufficient to activate a post curing phase. The degradation phenomenon, due to plasticization, subsequently analysed in detail, is more evident. Both the ultimate load and the initial stiffness of the P- δ curve were halved. Furthermore, the mechanical response was changed, from a ductile behaviour (elastic and post-elastic stage) for the unaged specimen to a linear elastic for the aged ones. 2.3 Influence of the desorption phenomenon on the fracture energy in mode II The influence of the desorption phenomenon on the fracture energy in mode II was evaluated with reference to only Araldite. The results are collected in Table 2 where symbols assume the same meaning of those of Table 1.

Table 2. Test results relating to the SLJ specimens after the desorption period. End of Elastic Stage

End of Post-Elastic Stage

End of fracture propagation

P nl [N]

δ nl

G II, Pnl [N/mm]

P max [N] 3129 0,10 2378 0,01 2038 0,00

δ max [mm] 5,26 0,11 4,18 0,04 3,77 0,01

G II, Pmax [N/mm]

P u

δ u

G II, Pu [N/mm]

[mm] 3,30 0,03 3,34 0,10 2,92 0,00

[N]

[mm] 6,68 0,11 7,43 0,07 8,11 0,02

μ

2053 0,03 1995 0,05 1663 0,00

0,59 0,10 0,57 0,27 0,42 0,00

1,97 0,37 1,11 0,09 0,87 0,02

2941 0,11 2840 0,13 2636 0,06

4,11 0,34 4,39 0,18 4,74 0,12

Unaged

σ 2

Aged SW,A+D Aged TW,A+D

μ

σ 2

μ

σ 2

A= continuous absorption, D= continuous desorption