Issue 47

M.F. Funari et alii, Frattura ed Integrità Strutturale, 47 (2019) 277-293; DOI: 10.3221/IGF-ESIS.47.21 292 C ONCLUSIONS he proposed model is developed with the purpose to study the behavior of sandwich structures affected by debonding phenomena and macrocrack in the core region. The numerical model is inspired by the previous works of the authors, performed in the framework of the layered structures and here generalized to sandwich structures. In this work, the numerical model is based on a 2D plane stress formulation to simulate the internal core, whereas the face- sheets follow a one dimensional model based on Timoshenko beam kinematics. In order to describe the delamination process, the proposed approach combines ALE formulation with a CZM. Moreover, crack growth in the core is predicted by a 2D moving mesh approach, in which a proper fracture criterion and mesh refitting procedure are introduced to predict crack tip front direction and displacement. Compared to existing formulations available in literature, this model presents lower computational complexities in the governing equations. In particular, the combination between CZM and ALE formulations, gives the possibility to introduce nonlinear interface elements in a small region containing the crack tip front, whereas in the remaining a coarse discretization is considered. In the model here proposed, macro-cracks at core/skin interface or in the core are decoupled during the crack evolution, therefore future developments are required to predict interaction phenomena, such as coalescence or initiation mechanisms. However, comparisons with numerical and experimental results, developed in both static and dynamic frameworks, show the capability of the proposed model to predict interfacial debonding phenomena at core/skin interfaces or the evolution of internal macrocracks in the core. A CKNOWLEDGEMENTS he authors acknowledge Frank McCauley and Jeremy Moore from Diab Limited UK for kindly providing the foam core material that was employed in the experimental section of this work. This work is also supported by Italian Ministry of University and Research (P.R.I.N. National Grant 2015, B86J16002300001) and SRPe (Scottish Research Partnership in Engineering) under the PECRE 2017/18 Scheme. R EFERENCES [1] Spadea, S., Orr J., Ivanova K. (2017). Bend-strength of novel filament wound shear reinforcement. Composite Structures, 176, pp. 244-253. [2] Ascione, L., Berardi V. P., Giordano A., Spadea S. (2015). Pre-buckling imperfection sensitivity of pultruded FRP profiles. Composites Part B: Engineering, 72, pp. 206-212. [3] Carlsson, L. A., Kardomateas G. A. (2011). Structural and Failure Mechanics of Sandwich Composites. York SDHLN, Springer Dordrecht Heidelberg London New York, Springer. [4] Mortas, N., Reis P. N. B., Ferreira J. A. M. (2014). Impact response of balsa core sandwiches. Frattura ed Integrità Strutturale, 30, pp. 403-408. [5] Morada, G., Vadean A., Boukhili R. (2017). Failure mechanisms of a sandwich beam with an ATH/epoxy core under static and dynamic three-point bending. Composite Structures, 176, pp. 281-293. [6] Tumino, D., Ingrassia T., Nigrelli V., Pitarresi G., Urso Miano V. (2014). Mechanical behavior of a sandwich with corrugated GRP core: Numerical modeling and experimental validation. Frattura ed Integrita Strutturale, 30, pp. 317- 326. [7] Rabinovitch, O. (2008). Cohesive interface modeling of debonding failure in FRP strengthened beams. Journal of Engineering Mechanics-Asce, 134(7), pp. 578-588. [8] Judt, P. O., Ricoeur A. (2015). Crack path predictions and experiments in plane structures considering anisotropic properties and material interfaces. Frattura ed Integrita Strutturale, 9(34), pp. 208-215. [9] Rashid, M. M. (1998). The arbitrary local mesh replacement method: An alternative to remeshing for crack propagation analysis. Computer Methods in Applied Mechanics and Engineering, 154(1), pp. 133-150. [10] Mi, Y., Aliabadi M. H. (1994). Three-dimensional crack growth simulation using BEM. Computers & Structures, 52(5), pp. 871-878. [11] Ingraffea, A. R. (2007). Computational Fracture Mechanics. In Encyclopedia of Computational Mechanics , E. Stein, R. Borst and T. J. Hughes, John Wiley & Sons, Ltd. T T