PSI - Issue 72

Thomas Steffen Methfessel et al. / Procedia Structural Integrity 72 (2025) 105–112

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curves for the critical crack length in Fig. 9, on the other hand, show that smaller adhesive thicknesses result in larger crack sizes and vice versa and also there is a jump in the curves. This jump is due to the non-monotonic behavior of the energy release rate. The available sandwich-type joint model and the strength assessment concept can also be applied to other structural configurations and load cases. As an example, the case of a CFRP (carbon fiber reinforced plastic) patch adhesively bonded by epoxy to a concrete substrate is to be considered (100mm patch length, 2mm thickness). Due to the mismatch in the thermal expansion properties under temperature change the CFRP patch tends to debond from the concrete substrate. For this situation Fig. 10 shows the calculated critical temperature change in dependence of the adhesive layer thickness, again with the effect of a reduced critical load for increased adhesive thickness. This kind of prediction can be done easily with the provided sandwich-type modeling and strength assessment and is of significant relevance for the practical application.

Fig. 10. Critical temperature and initiated crack length in dependence of the adhesive layer thickness.

7. Conclusions Concluding, it can be stated that the suggested higher-order displacement approach for the adhesive layer within the considered sandwich-type model clearly leads to predictions of higher accuracy and is well validated by comparative finite element calculations. Following the concept of Finite Fracture Mechanics, the approach also allows an effective strength assessment based on the coupled stress and energy criterion. The provided analysis and assessment tool involves only low computational effort but, nevertheless, is of good predictive quality. With that it is valuable for the actual practical application. References Bigwood, D. A., Crocombe, A. D., 1989. Elastic analysis and engineering design formulae for bonded joints. International Journal of Adhesion and Adhesives 9 (4), 229-242 Da Silva, L. F. M., Rodrigues, T. N. S. S., Figueiredo, M. A. V., Moura, M. F. S. F., Chousal, J. A. G., 2006. Effect of Adhesive Type and Thickness on the Lap Shear Strength. The Journal of Adhesion 82 (11), 1091-1115 Goland, M., Reissner, E., 1944. The stresses in cemented joints. Journal of Applied Mechanics 11 (1), A17-A27 Leguillon, D., 2002. Strength or toughness? A criterion for crack onset at a notch. European Journal of Mechanics – A/Solids 21 (1), 61-72 Methfessel, T. S., Mesbah, C., Becker, W., 2024. Failure analysis of crack-prone joints with Finite Fracture Mechanics, using an advanced modeling approach for the adhesive layer. International Journal of Adhesion and Adhesives 130, 103608 Ojalvo, I. U., Eidinoff, H. L., 1978. Bond Thickness Effects upon Stresses in Single-Lap Adhesive Joints. AIAA Journal 16 (3), 204-211 Volkersen, O., 1938. Die Nietkraftverteilung in zugbeanspruchten Nietverbindungen mit konstanten Laschenquerschnitten. Luftfahrtforschung 15 (1,2), 41-47