PSI - Issue 27

Tuswan Tuswan et al. / Procedia Structural Integrity 27 (2020) 22–29 Tuswan et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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quick turnaround in port. Moreover, the stern ramp can also serve as a watertight door when pivoted or folded into its closed position. The stern ramp/door is designed by assembling a sandwich panel on the top and bottom structure. The original stern ramp/door is entirely constructed by two stiffened steel plates connected by stiffener. The structure modification is completed by replacing the top and bottom plate of the ramp door with the sandwich panel. The modification of the stern/ramp door is calculated based on DNV-GL rules of steel sandwich panel construction to calculate the thickness configuration of the sandwich panel (DNV-GL, 2016). The calculation of thickness configuration based on DNV-GL using strength index criteria to fulfill the equivalent strength results in the configuration thickness of the top and bottom sandwich, as illustrated in Fig. 1. Sandwich panels compose the proposed stern ramp/door with dimension 8 m in length, 8.6 m in width, and 0.346 m in height. Based on the DNV-GL strength index calculation, the top and bottom sandwich panel is constructed to have a uniform configuration of faceplate and core material thickness. The configuration of the top and bottom sandwich thickness is 5-15-3 mm. Both longitudinal and transverse stiffener use I beam with using 300x40 mm in dimension. The complete configuration of the ramp door model is fully presented in Fig. 1.

Fig. 1. Configuration of the stern ramp/door model.

The proposed ramp door is constructed by two sandwich panels connected by stiffener between them. The sandwich panels use steel material as the faceplate and the combination of unsaturated polyester resin (UPR) and clamshell powder as core material. The longitudinal and transverse stiffener uses steel material. Several findings regarding the application of sandwich material in the ship’s structure have been conducted by using the same material type, such as in the side hull structure (Tuswan et al., 2019), in the car deck system (Tuswan et al., 2020). The mechanical properties of the stern ramp/door model are presented in Table 1.

Table 1. Mechanical properties of the stern ramp/door. Materials

ρ ( kg/m 3 )

E ( Pa )

υ

Faceplate

7850 1465

2.1 x 10 11 4.4 x 10 9

0.3 0.3

Core material

2.2. Debonding model development A review of literature presents that although extensive research has been conducted on the issue of free vibration of debonding problems, only a few outcomes are reported on predictions of the dynamic properties in terms of debonding shapes mainly analyzed in the complex ship structure such as stern/ ramp door. In this case, debonding is assumed to be located on the interface between the top faceplate and the upper part of the core material of the bottom sandwich panel. The debonding is treated as an artificial imperfection at the interface layer between two layers. It is expected that debonding shapes can be used as the sensitivity parameter of the internal damage occurrence. To achieve that purpose, the varying shapes of debonding is used. The planar size of prescribed debonding is defined by a damage parameter ( D % ) denoting the ratio of the debonded area ( A d ) to the entire area of the interface of the