PSI - Issue 37

Jani Romanoff et al. / Procedia Structural Integrity 37 (2022) 17–24 Romanoff et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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As can be seen, the fully fixed case results in more even dZ/dy-distribution, especially at the end of the stiffeners, which indicates more uniform membrane stretch in the panels due to von Karman strains. At the same time, we see that the curvature associated with bending deformations is less and much more localized, to the center region of the panels. When longitudinal edges are allowed to pull in straight lines, the membrane stretch is less uniform, and bending is activated more. In this case, the projected area of the opening is more extensive, which would mean in the ship collisions or grounding a larger inlet, leading to more rapid flooding of the damaged compartments. 4. Conclusions This experimental campaign showed that it is essential to consider the influence of actual boundary conditions and welds in the strength modeling of steel structures. The boundary conditions contribute directly to the load-carrying mechanism and how much external loading is carried out by membrane and bending actions. The consequences are seen both at the absorbed energy levels and at the shape of the opening the penetrator makes. In addition, it was shown that the initial imperfection shape seems not to explain much to the actual outcome of quasi-static collision tests on web-core panels. Still, the influence of loading, material, and structural gradient explain why these advanced structures, which are very effective on carrying loads especially at linear range, become unpredictable and absorb less plastic energy under accidental loads. The investigations also show the importance of time in the assessment of both load and response of structures. In web-core panels where the gradients occur spatially at the same place, the failure may be rapid even though the loading is quasi-static and slowly applied. The presented investigation was limited to measurements at room temperature and scanning the specimens only after the experiment. In case of lower temperatures, the failures could become even more sudden. Also, as the experiments show, it would be very useful to measure the deformations and strain during the experiment, and this way trace better the load-carrying mechanism of the panels as it evolves. This is not an easy task as the scanning takes time, and the oscillations of the displacement-controlled impactor will affect the quality of scanning. On the other hand, Digital Image Correlation measurements for strains are not easy due to the test setup and significantly deforming specimens, leaving very little space for the measurements below the indenter. In order to remove these deficiencies, the test set-up would need modifications. Therefore, these issues are left for future work. Acknowledgements The experimental program would not have been possible without the project called Ultra Lightweight and Fracture Resistant Thin-Walled Structures through Optimization of Strain Paths, by the Academy of Finland (310828). This work was also supported by the Estonian Research Council grant PSG526. This financial help is gratefully acknowledged. Also the authors would like to thank Veijo Laukkanen for his help on executing the experiments. References Bulgen, L., Le Sourne, H., Besnard, N. and Rigo, P., 2012. Extension of the super-elements method to the analysis of oblique collision between two ships. Marine Structures, 29(1) 22-57. DOI: 10.1016/j.marstruc.2012.08.002 Frank, D., Romanoff., J and Remes, H., 2013. Fatigue strength assessment of laser stake-welded web-core steel sandwich panels. Fatigue and Fracture of Engineering Materials and Structures, 36(8), 724-737. DOI: 10.1111/ffe.12038 Kim, S.J., Kõrgesaar, M., Ahmadi, N., Taimuri, G., Kujala, P. and Hirdaris, S., 2021. The influence of fluid structure interaction modelling on the dynamic response of ships subject to collision and grounding. Marine Structures 75(1), 102875, DOI: 10.1016/j.marstruc.2020.102875. Kõrgesaar, M., Romanoff, J. and Palokangas, P., 2016. Penetration resistance of stiffened and web-core sandwich panels: experiments and simulations. Aalto University, Department of Mechanical Engineering, Finland. ISSN 1799-490X (pdf). Kõrgesaar, M., Romanoff, J., Remes, H. and Palokangas, P., 2018a. Experimental and numerical penetration response of laser-welded stiffened panels. International Journal of Impact Engineering 114(1), 78 – 92, DOI: 10.1016/j.ijimpeng.2017.12.014 Kõrgesaar, M., Romanoff, J. and Palokangas, P. 2018b. Experimental and numerical assessment of fracture initiation in laser-welded webcore sandwich panels. Eighth International Conference on, Thin-Walled Structures - ICTWS 2018, Lisbon, Portugal, July 24 – 27. Le Sourne, H., Besnard, N., Cheylan, C. and Buannic, N., 2012. A Ship Collision Analysis Program Based on Upper Bound Solutions and Coupled with a Large Rotational Ship Movement Analysis Tool, Journal of Applied Mathematics, ID 375686, 27 pages, DOI 10.1155/2012/375686. Pedersen, P.T. 2010. Review and application of ship collision and grounding analysis procedures. Marine Structures, 23(3), 241-262. DOI: 10.1016/j.marstruc.2010.05.001