PSI - Issue 68

Ihssane Kididane et al. / Procedia Structural Integrity 68 (2025) 358–364

362

Ihssane Kididane et al. / Structural Integrity Procedia 00 (2024) 000–000

5

5

Cohesive fracture pattern (SLB test agreeing with references from literature)

4.5

4

3.5

3

2.5

Adhesive fracture in interphase substrate/adhesive (example for all other SLB /CMMB)

2

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1

0.5

Direction of crack growth

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0

Fig. 3. Experimental results at constant mode-mixity, φ = 41 ◦ . Left: fracture energy, Right: exemplary fracture patterns.

of the interface rather than properties of the adhesive layer, there appears to be a similar qualitative dependence on layer thickness between them.

3.2. Mode I fracture

The initial mode I loading in the CMMB tests was evaluated in a first step to determine the dependence of the mode I fracture energy J Ic on the adhesive layer thickness. Fig. 4 shows the obtained crack resistance curves as well as the averaged values of fracture energy for the di ff erent adhesive layer thicknesses. The equivalent crack growth ∆ a eq = a eq − a eq , 0 was calculated by Eq. 5 with a eq , 0 = (304 . 5 ± 4 . 1)mm 1 being the initial value of a eq before crack propagation. Within the strongly scattering adhesive layer thicknesses, the expected (Marzi et al., 2011) increasing trend in J Ic with increasing t adh is indicated.

3

3

2.5

2.5

2

2

1.5

1.5

1

1

0.5

0.5

0

0

0

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1

1.5

0

20

40

60

80

100

Fig. 4. Mode I fracture during initial loading. Left: R-curves, Right: J Ic vs. t adh .

3.3. CMMB results at varying mode-mixity

Fig. 5 shows the obtained fracture envelopes from CMMB tests in two forms of presentation. In order to exclude falsification of the fracture envelopes due to possible crack rest, points are shown only if the crack has grown by an

1 The di ff erence between the equivalent and the (real) nominal initial crack length ∆ 2 = a eq , 0 − a 0 ≈ 24 mm is in the expected range, Kididane et al. (2024) reported ∆ 2 = (26 . 7 ± 0 . 2) mm for another structural adhesive.