PSI - Issue 81

Anandito Adam Pratama et al. / Procedia Structural Integrity 81 (2026) 58–65

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based on the folded plate concept; the X-core originates from auxetic or re-entrant honeycomb designs; and the Y-core combines truss and hexagonal concepts. The panel design and materials of the sandwich panels are developments of the stiffened panel shape previously used by Alsos and Amdahl (2009). The four variations of sandwich panel designs studied are shown in Fig. 2.

Fig. 2. Geometry of core sandwich panel: (a) S-core, (b) U-core, (c) X-core, and (d) Y-core.

The sandwich panel consists of a 5 mm face plate and a 6 mm core, with core dimensions shown in Fig. 2. The panel has an overall width of 720 mm and a length of 1200 mm, and both the face plate and core are made of high-strength steel S355NH EN10210, with a density of 7850 kg/m³ and an elastic modulus of 210 GPa. The material response is defined using the Cowper– Symonds hardening model with parameters D = 40 s ⁻ ¹ and n = 5, while the engineering stress – strain relationship is illustrated in Fig. 3 based on the study of Alsos and Amdahl (2009). The surrounding water domain is modelled as a semi-circular region to allow wave propagation in all directions, represented as an acoustic fluid with a density of 1000 kg/m³ and a bulk modulus of 2.1 GPa.

5.00E+08

4.00E+08

3.00E+08

Core Plate

2.00E+08

Stress (Pa)

1.00E+08

0.00E+00

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Strain

Fig. 3. Engineering stress-strain curves for sandwich panel component materials.

Boundary conditions are applied to both the structural and fluid domains. For the sandwich panel, fully clamped (encastre) boundary conditions are imposed on all four edges, constraining both translational and rotational degrees of freedom. This boundary condition represents a local structural component rigidly connected to a much stiffer surrounding structure, such as a panel segment integrated into a ship hull or supported by longitudinal and transverse stiffeners, where edge deformations are significantly restrained. In the water domain, an acoustic-impedance non-reflecting boundary condition is applied to minimize artificial wave reflections, and the initial fluid condition is set to zero acoustic pressure at the designated boundaries. The underwater explosion (UNDEX) loading is modelled using the Abaqus incident-wave interaction approach with TNT as the explosive material, with the structure fully submerged at 2 m depth. The structural domain is discretized using S4R shell elements with a mesh size of 0.015 m, adopted from a validated reference sandwich panel model. A mesh convergence study has been conducted on the S-core model with a stand-off distance of 2 m and a TNT mass of 4 kg to verify mesh independence; the results are summarized in Table 2. The fluid domain is meshed with AC3D8R acoustic elements using a mesh size of 0.01 m. The complete simulation configuration schematic is shown in Fig. 4.