ABSTRACT

In this paper, the applicability of health monitoring is discussed for crack-type damages of metal ship structures. Three types of line sensors, i.e. conductive film sensor, the conductive paint sensor and the plastic optical fiber sensor, are made on an experimental basis. The sensors are bonded on the surface of a welded Joint model and a notched plate specimen by adhesives or painting, and fatigue tests are carried out. Based on the results of the experiments, the performances of each type sensor are discussed. Further, the significance of direct monitoring of damages and failure events on ships and the selection criterion of the health monitoring members in ship structure are made clear.

INTRODUCTION

Recently, there has been a growing interest in the so-called intelligent or smart structures, among which is the idea of the health monitoring. The aim of the health monitoring is to provide real time and continuous safety assurance of structure by a sensor network spread in the structure. This network emulates the nerve system of the human body. Fatigue cracks, buckling and excessive deformations induced in the structure are the main objects of the monitoring. This concept has evolved since the Aloha Boeing 737 accident in April 1988, as a promising approach to maintain structural safety instead of repeated in-service inspections. Some methods of employing fiber-optic sensors have been proposed to monitor the internal deformations and cracking of aircraft structures, within the composite layers of which fiber-optic sensors are embedded. Of course, monitoring of several items on ships has been performed. However, the direct monitoring of structural damages or failure events have been scarcely carried out, yet. This is re garded as being the following reasons. (1) There is no such sensor which has excellent performance of sensing fatigue cracks or buckling, and (2) There are a lot of hot spots which are susceptible of damages in ship structures moreover, these members are arranged with pretty long distances among members.

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