PSI - Issue 47

Jaroslav Václavík et al. / Procedia Structural Integrity 47 (2023) 282–289 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Again the node was tested without CFRP stiffening, with the one-side CFRP and with double side CFRP plate length 550 mm from upper and bottom side. To make it possible to glue the plate over the welds, the upper transversal welds were grinded out to the surface level. The transversal welds were stiffened with the CFRP plates, which beginning and ends were positioned to areas with operational stresses lower than the debonding threshold. The comparison of strain response at strain gauges during fatigue test at the weld and at the end of CFRP plate is presented in Fig. 9a. The crack appears several million cycles at the transversal weld under the CFRP plate at the same position, as at the non-stiffened join (Fig. 8b), but after higher number of cycles (Fig. 9b). However, when the stiffening is made only from one side of the profile, the stress is increased on the opposite side which leads to lower fatigue life of the profile. Nevertheless the CFRP plate is not debonded on both cases. 4. Conclusions The use of stiffened hollow profiles with the CFRP plates can on several joints increase the strength of the bus structure. This results in an increase in service life and a delay in the occurrence of cracks and their propagation. The beginnings and ends of the CFRP plates must lie in areas of the debonding limit stress. These areas can be determined using FEM calculation and verified using measurement with strain gauges. In properly designed hybrid structure the hybrid beams must not delaminate during the bus service life to be able withstand the roll over accident. In the project, some stiffened structure parts were tested in the laboratory. Currently, there is an effort to use reinforcement on buses in real operation. Acknowledgements The article has originated in the framework of M-ERA.NET call 2019 and was supported with Technological Agency of Czech Republic under the No. TH71020003. References Jahn J at al. Assessment strategies for composite-metal joining technologies – A review. 26th CIRP Design Conference, Procedia CIRP 50 (2016), 689 – 694. Bocciarelli, M., Colombi, P., Fava, G. & Poggi, C. 2014, Some issues on the strengthening of steel structures with fibre-reinforced polymer materials, Australian Journal of Structural Engineering, Vol. 15, No. 4, October, 337-354. Kamruzzaman, M. et al. A Review on Strengthening Steel Beams Using FRP under Fatigue. Scientific World Journal, Volume 2014, Article ID 702537, 21 pages. Colombi, P, Fava, G., Sonsogni, L. Fatigue crack growth in CFRP-strengthened steel plates, Composites: Part B 72 (2015) 87–96. Zhang, L., Cao, S. and Tao, X. Experimental Study on Interfacial Bond Behavior between CFRP Sheets and Steel Plates under Fatigue Loading, Materials 2019, 12, 377; doi:10.3390/ma12030377. Vatandoost, F. Fatigue Behaviour of Steel Girders Strengthened with Prestressed CFRP Strips. https://www.researchgate.net/ publication/268412445 (2010). Laubrock, M. Design of load-bearing adhesive joints in agricultural machinery. Sika Vehicle Manufacturing Days 2022. Meschut, G. at al., Lifetime prediction of hybrid joints, FAT-Schriftenreihe 326, Forschungsvorhaben IGF-Nr. 19187 BG, 2020. Liu, H.; Xiao, Z.; Zhao, X.L.; AI-Mahaidi, R. Prediction of fatigue life for CFRP-strengthened steel plates. Thin-Walled Struct . 2009, 47, 1069– 1077. Wu, C., Zhao, X.L., Chiu, W.K, Al-Mahaidi, R., and Duan, W.H., Effect of fatigue loading on the bond behavior between UHM CFRP plates and steel plates. Coposites Part B: Engineering, 20123.