The sandwich plate can be used to replace the conventional steel stiffened plates on the ship’s hull structure. By using the sandwich plate, not only the stiffness of the plate can be increased but also the overall ship weight can be reduced, as well as the ship payload can be increased. The sandwich plate should be accompanied by the damage identification system to prevent ship structural failure. In this paper, the global damage identification method, which is based on the vibration analysis, is investigated. For that purpose, the vibration-based damage identification using the Finite Element Method (FEM) is explored. The variables being investigated are the damage sizes, damage locations, and the boundary conditions which affect the natural frequencies of the structures. The sandwich plate considered in this study consisted of steel faceplates with the polyurethane elastomer core, which has been checked to meet Lloyd’s register, an international maritime standard. From the analysis, it is found that the fully clamped boundary conditions accompanied by high vibration modes are more sensitive to the presence of artificial damage. The changes in the natural frequencies can be used as a reference to identify the size and location of damage in the sandwich plate.

The implementation of a sandwich panel on the marine structure needs better knowledge of mechanical behaviour, primarily static and dynamic response. The static and dynamic response is investigated due to the application of a sandwich panel on the ferry ro-ro ramp door using finite element software ABAQUS. Five modification models using different sandwich thickness and stiffener configuration were compared using static analysis to analyze a comparison of structural strength and weight saving. Additionally, the dynamic response was also investigated due to debonding problem. The influence of debonding ratio, geometry, number of debonding, debonding depth, debonding location, and boundary condition was carried out. Debonding was estimated by using free vibration analysis where the Lanczos method for Eigen values extraction was applied. Result of the static analysis showed that Model C caused an increase in strength to weight ratio compared to the existing model. Furthermore, the natural frequency was being calculated as modal parameters to investigate the debonding problem. The natural frequency of the debonded model decreased due to discontinuity in the damaged area. The dynamic response using natural frequency change can be performed as a structural health monitoring technique.

A lightweight sandwich plate system (SPS) consisted of steel faceplate and polyurethane elastomer composite cores have excellent potential to be applied on the ship structure. Steel faceplate and polyurethane elastomer (PU) cores are frequently applied, but PU has a relatively high material cost. More economical material can be achieved by combining PU with fiberglass as a fiberglass reinforced polyurethane elastomer (FRPU) composite. In this study, the sandwich consisting of steel faceplate and FRPU composite core material is applied in the tanker side hull by investigating the structural performance and weight saving analysis using finite element analysis (FEA). Four sandwich side hull models using different stiffener configurations are compared with the conventional stiffened plate model. The results show the promising SPS application on structural strength and weight reduction. The remarkable stress reduction, deformation, and structural weight reduction due to SPS application are discussed. Therefore, its weight reduction can increase the ship payload so that ship operations will be cost-effective.

As one of the most dangerous defects in the sandwich panel, debonding could significantly degrade load carrying capacity and affect dynamic behaviour. The present work dealt with debonding detection of the rectangular clamped hybrid sandwich plate by using ABAQUS software. The influence of various damage ratios on the linear and nonlinear dynamic responses has been studied. The finite element model was initially validated by comparing the modal response with the experimental test. Rectangular debonding was detected by comparing dynamic responses of free and forced vibrations between intact and debonded models. A wide range of driving frequency excitation corresponding to transient and harmonic concentrated loads was implemented to highlight nonlinear behaviour in the intermittent contact in the debonded models. The results showed that debonding existence contributed to the natural frequency reduction and modes shape change. The numerical results revealed that debonding affected both the steady-state and impulse responses of the debonded models. Using the obtained responses, it was detected that the contact in the debonded region altered the dynamic global response of the debonded models. The finding provided the potential debonding diagnostic in ship structure using vibration-based structural health monitoring.

Rizky Chandra Ariesta, Achmad Zubaydi, Abdi Ismail, Tuswan Tuswan; Original scientific paper, pp. 1-8 Download