PSI - Issue 26

S.M.J. Razavi et al. / Procedia Structural Integrity 26 (2020) 225–228 Razavi et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3. Results and discussion

Fig. 2 illustrates the fatigue life results obtained from fatigue test of both non-reinforced and reinforced adhesive joints. According to the experimental data a clear fatigue life improvement can be observed for the reinforced adhesive joints. This fatigue life improvement is a function of fiber distance. Lower fiber distance or higher weight percentage of the reinforcing fibers enhances the fatigue strength of the joint. During the fatigue tests, damage initiated from the overlap ends changing the color of the adhesive layer to a brighter color. According to previous research by Khoramishad and Razavi (2014), the transferred load in the reinforced adhesive joints was shared between the adhesive layer and the reinforcing fibers resulting to higher strength of the joint. By extension of the fatigue crack through the adhesive layer to some extent, the fibers started to pull out from the adhesive layer. Fig. 3 illustrates the fiber pullout mechanism after the joint failure under fatigue loading. Incorporation of the metallic fibers to the adhesive layer results in lower peak stresses along the bonding length, which increases the load bearing of the adhesive joints. On the other hand, due to the higher thermal conductivity of metallic fibers compared to the adhesive, metal fibers can provide better temperature distribution in the adhesive layer during curing process resulting in a lower residual stress level. It is worth mentioning that although reducing the fiber distance improved the fatigue performance, there is a practical limit for reducing the fiber distance. In critically small distances, the risk of incorporating air voids in the bond line increases, which can reduce the efficiency of the method. Further studies need to be performed to evaluate this point.

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Load amplitude (N)

Non-reinforced a=1.9 a=0.9

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0

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100,000

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Number of cycles to failure

Fig. 2. The load-life diagram for the tested adhesive joints.

Fig. 3. Reinforced adhesive joint with fiber spacing of a = 0.9 failed under fatigue loading.