PSI - Issue 54

I.R.S. Araújo et al. / Procedia Structural Integrity 54 (2024) 406–413 Araújo et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Damage analysis This section presents the study of the stiffness degradation (SDEG) damage variable for the various joint configurations. This variable represents the percentile degradation of the cracked elements compared to a purely linear behavior. The study of the SDEG damage variable of the elements of the adhesive layer, along x / L O , is one of the tools that helps to compare the various joint configurations for the different adhesives. This variable has values between 0 (undamaged material, up to peak stress) and 1 (failure), providing the degradation of the stiffness of the damage law under mixed-mode conditions. Fig. 5 shows the extent of damage (SDEG) at the instant of P m with the normalized length of the adhesive layer ( x / L ), in scarf joints with different  bonded with the adhesives AV138 (a), 2015 (b) and 7752 (c). Plot analysis shows that the greatest incidence of damage in this type of joint takes place at the adhesive layer ends, thus in agreement with the distribution of stresses presented in previous works (Alves et al. 2018). At the middle of the adhesive layer, damage is typically zero when P m is reached. The comparison between different  shows that, as this geometrical parameter increases, there is less localized damage at the ends and more uniform damage throughout the adhesive layer, which also agrees with the documented variation of stress distributions as a function of  (Silva et al. 2018), since stresses also become more uniform for higher values of  . Between adhesives as their stiffness increases, the magnitude of the damage in the various  increases and is concentrated in smaller areas at the ends of the bond, showing more oscillations. On the other hand, the increased ductility of the adhesive allows for a more uniform distribution of damage at the instant of P m , which leads to better utilization of the adhesive’s strength throughout the bond length. Comparison of these plots with those known for DLJ (Nunes et al. 2016), it can be concluded that damage is much more uniform across the adhesive layer. Thus, while in SLJ the adhesives’ ductility plays a significant role on strength, it is expected that, for scarf joints, the bulk strength of the adhesives becomes more relevant to achieve higher P m .

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Fig. 5. SDEG evolution at P m as a function of x / L for scarf joints bonded with the AV138 (a), 2015 (b) and 7752 (c).

3.3. Joint strength Fig. 6 shows the P m values obtained experimentally and numerically using the XFEM for the scarf joints bonded with the adhesives AV138 (a), 2015 (b) and 7752 (c). Evaluation of the AV138 results shows that the XFEM prediction for the scarf joints with  =3.43º (23.69 kN) does not match the result obtained experimentally (29.7 kN).