## 5 Concluding Remarks  
An experimental and numerical study on the response of sandwich panels with aluminium skins and extruded polystyrene foam cores exposed to blast loading has been presented. The main contribution from this work is the large amount of high-precision experimental data together with a validated numerical modelling strategy that may be used to improve simulation-based optimisation techniques of sandwich panels exposed to blast loading. The constitutive behaviour of the aluminium skins and polystyrene foam cores was characterised through series of quasi-static material tests. In addition, the dynamic response of the foam cores was investigated through low-velocity impact tests. The results from the quasi-static tests were used to calibrate the modified Johnson-Cook material model for the skins and the Deshpande-Fleck material model for the foams. The material models were in general able to describe the quasi-static behaviour of the materials. An extension of the Deshpande-Fleck crushable foam model was implemented as a user-material subroutine in LS-DYNA to account for both the density distribution and the viscoplastic behaviour of the foams. When compared to the results from the low-velocity impact tests, the extended Deshpande-Fleck model was able to represent the viscoplastic behaviour of the core materials with reasonable accuracy. In the blast load tests, sandwich panels with the different foam core materials were subjected to various blast load intensities. The failure load increased significantly for the sandwich panels compared to skins only. This increase was especially evident when comparing the results at the intermediate blast load. In general, the response of the test specimens in terms of back-skin displacement and core compaction correlated with the density of the foam core, and a lower density core gave a higher displacement of the back skin. Some discrepancies to this trend were however observed regarding fracture of the sandwich panels, since in one test the panel with intermediate core density failed while the others did not. Fracture of the panels may, on the other hand, be mitigated without changing the weight of the component by using a stronger or more ductile aluminium plate for the skins. The numerical simulations captured the trends observed experimentally. They also showed that a model that takes the density distribution across the core into account dissipates more energy than a model with constant density, which confirms that a graded density foam core would be preferable in an energy absorbent. A viscoplastic formulation of the core material reduced the core compression and energy absorption. In this study, FSI effects were not considered, and the numerical simulations provided in general conservative results in terms of back skin displacement. It is however expected that including FSI in the modelling approach would scale the results proportionally so that the main trends will still be captured. K.A.B. : Formal analysis, methodology, investigation, visualization, writing--original draft preparation, writing-review and editing. A.R. : Conceptualisation, writing--original draft preparation, writing--review and editing. T.B. ([PERSON]): Formal analysis, software, writing--review and editing. M.L. : Writing--review and editing, supervision, funding acquisition. T.B. ([PERSON]): Conceptualisation, writing--original draft preparation, writing--review and editing, supervision, funding acquisition. All authors have read and agreed to the published version of the manuscript. The present work has been carried out with financial support from the Centre of Advanced Structural Analysis (CASA), Centre for Research-based Innovation, at the Norwegian University of Science and Technology (NTNU) and the Research Council of Norway through project no. 237885 (CASA). The authors would like to acknowledge the assistance of [PERSON], [PERSON], [PERSON] and [PERSON] with the various experimental programs. The authors declare no conflict of interest.