## 3 Proposed Sandwich Panels  
Corrugated cores are stiff and strong in the longitudinal direction, but weak in the transverse direction [30]. The simplest approach to overcome this is by placing corrugated cores aligned with both the longitudinal and transverse directions of the panel. The new configuration consists of corrugated strips placed in two perpendicular directions, forming the ribbon core (RC) depicted in Figure 5. Two different geometries for RC were used in this study, the trapezoidal ribbon core (TZRC) and the triangular ribbon core (TRC). They were designed with the geometric parameters for the TZ and T cores in order to highlight the impact of the new technique on the blast performance of sandwich structures. The relative density (\(\overline{\rho}\)) for the TZRC and TRC were 2.28 and 2.84, respectively. So, the novel topologies use a lesser amount of material compared with the traditional corrugated cores by about 64% for the TZRC and 56.9% for TRC. The width of each strip (b) was 7 mm, the height (h) was 14 mm and the thickness (t\({}_{\text{c}}\)) was 0.7 mm. The panel had the same dimensions used for the TZ and T panels. The RC structures exposed to a detonation of 55 g of TNT explosive charge located over the center of the panel with 100 mm _SoD_. Autodyn used to numerically investigate the dynamic response of the RC panels under the impact of the blast load. Figure 4: Comparison between the experimental and numerical results of deformation/failure modes due to detonation at stand-off distances (_SoDs_) of 50, 100, and 150 mm. (**a**) TZ-panel. (**b**) T-panel. Previous studies [14] revealed that the behavior of the sandwich structure subjected to blast load can be split into three stages, namely the fluid-structure interaction stage, core compression stage, and structural dynamic response stage. Figure 5 shows a series of deformation processes of TZRC and TRC panels subjected to the detonation of 55 g TNT with a stand-off distance of 100 mm. Figures 6 and 7 show the panel at time t = 0 after remapping the final state of the 2D model to a 3D model just before the impulse is imparted to the front-face sheet of the sandwich panel. Then, at t = 0.001 msec, the shock wave firstly strikes the center of the front-face sheet. From this moment on, the front face was starting to interact with the explosive product. During the fluid-structure interaction stage, the front face obtained an initial velocity when the shock wave impinged on it, while the core and back face kept still. A dent deformation was first formed in the central area of the front face, Figures 6 and 7. Then, the high compression velocity generated by the front face induced a shock wave into the core and the core would be compressed gradually at t = 0.03 msec. It could be seen that the compression of the shock wave is more compressed than the front face. Figure 5: Schematic and inner core configuration of the ribbon core sandwich structures. (**a**) Trapezoidal corrugated ribbon core (TZRC)-panel. (**b**) Triangular ribbon corrugated core (TRC)-panel. core decreased from the center to the peripheral region as displayed in Figures 6 and 7c. During this stage, the front face was decelerated by the core while the core and the back face were accelerated. At the end of the core compression stage, the panel components obtained the same velocity and went into a phase of structural dynamic response under their own inertia. The dent deformation extended outwards and downwards with the transfer of momentum, Figures 6 and 7d. Then, the panel went into an oscillation until the kinetic energy was gradually dissipated by plastic bending and stretching. Finally, at t = 10 msec, the panel underwent residual deformation as shown in Figures 6 and 7e. Figure 8 illustrates the midpoint velocity and deformation/time histories of face sheets. As exhibited in Figure 8a, the velocity at the midpoint of the front-face sheet quickly reaches its maximum value at the beginning of the response, and then gradually decreases due to core compression.