Development of Crack Monitoring Sensor for Ship Structure

讨论了结构监测在金属船舶和近海构筑物裂纹型损伤中的适用性。检查了两种类型的监测方法；现有裂纹的感知和裂纹损伤的预测。作为现有裂缝的感知，采用了健康监测的概念。实验制作了导电薄膜传感器、导电涂料传感器、塑料光纤传感器、玻璃光纤传感器和碳纤维传感器五种线路传感器。将传感器通过粘合剂或涂料粘接在焊接接头模型和两类试件表面，并进行疲劳试验。在这些试验中，密切观察了疲劳裂纹破坏传感器的现象。此外，通过测量传感器的电阻或激光束的光强输出来感知疲劳试验中失效的瞬间。根据实验结果，讨论了各类型传感器的性能。为了预测疲劳损伤，研究了在构件上附加牺牲试样的方法。牺牲试样的设计使构件的应力被放大，从而导致比构件更早的裂纹萌生。为此，研制了长60mm、宽10mm、厚0.25mm的矩形薄板，中间有人工裂缝。在试样长度的中间部分涂上聚四氟乙烯薄膜，整个试样夹在两块薄环氧树脂板之间。将牺牲试样用环氧树脂粘接在光滑疲劳试样上，在脉动拉伸和全反应力条件下进行疲劳试验。试验结果表明，本研究开发的牺牲试样可以预测两种应力条件下构件的疲劳起裂。

The applicability of structural monitoring is discussed for crack-type damages of metal ships and offshore structures. Two types of monitoring methods are examined ; perception of existing crack and forecast of crack damage.As the perception of existing crack, the concept of health monitoring is employed. Five types of line sensors, i.e. conductive film-sensor, conductive-paint sensor, plastic optical-fiber sensor, glass optical-fiber sensor and carbon-fiber sensor are made on an experimental basis. The sensors are bonded on the surface of a welded joint model and two types of specimens by adhesives or painting, and fatigue tests are carried out. In these tests, the appearance that the fatigue cracks break the sensors is closely observed. Further, electric resistance of sensors or light strength output of laser beam are measured to perceive the instant of failure during the fatigue test. Based on the results of the experiments, performances of each type sensor are discussed.In order to forecast fatigue damage, method to attach sacrificial specimen on member is examined. Sacrificial specien is designed such that magnified member stress is transmitted to the specimen and thus results in earlier crack initiation than the membe. For this purpose, a rectangle thin plate with 60mm-length, 10mm-width and 0.25mm-thick, which has an artificial crack in the center, is developed. The middle part in length of the specimen is coated by teflon film and the whole of the specimen is sandwiched in between two thin epoxy resin plates. The sacrificial specimen is bonded on a smooth fatigue specimen by epoxy resin, and fatigue tests were carried out under pulsating tension and fully reversed stress conditions. From the test result, it is concluded that the sacrificial specimen developed in this study can forecast the fatigue initiation of member for both stress conditions.