PSI - Issue 19

Hiroyuki Oguma et al. / Procedia Structural Integrity 19 (2019) 224–230 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 8. High- magnification view of the region “A” in Fig. 7(b).

Regarding the fatigue test specimens, fracture parts which obtained in the short life regime under R = − 1, − 0.5 and 0.1 mainly showed cohesive failures, and the general surface aspect resembles that obtained in the tensile tests. In the long life regime, adhesive layer is filled with fine cracks, and glass fibers appear partially in the fracture parts as shown in Fig. 9. On the other hand, when R > 0.5, the appearance of the glass fibers occurs from shorter life regime. Change of the failure mode, from cohesive failure to adherend failure, probably relates to the effect of mean load on the fatigue strength properties as shown in Fig. 6.

a

b

B

Fig. 9. Fracture surface obtained in the fatigue test (as-received, R = 0.1, P max = 1200 N, N f = 6.10 x 10 6 ) (a) overview; (b) high- magnification view of the region “B” .

5. Conclusions

Tensile-shear tests, fatigue tests under different stress ratio conditions and fracture surface observations were carried out to investigate the effects of mean load on fatigue properties of adhesively bonded structures. The effects of mean load were observed under higher stress ratio conditions, and fatigue strength at 10 7 cycles dramatically deceased when the stress ratio was larger than 0.5. The observations revealed that change of the failure mode from cohesive failure to adherend failure probably relates to the effect of mean load on the fatigue strength properties.