STUDY ON DAMAGE TORERANT DESIGN OF SHIP STURUCTURES

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Damage tolerant design is a design method of structures considering in-service-inspections, repair actions and structural monitoring at the design stage. In this study, the following five research items related with damage tolerant design are carried out.(1) high-sensitivity sacrificial specimen for stress monitoring.(2) stress history measurement sensor using piezoelectric element.(3) inspection supporting system of ships by the use of product model.(4) inspection planning of ship structures considering corrosion effects.(5) inherent damage zone model for fatigue strength evaluation.Among them, remarkable results are obtained for the items (1) and (2).High-sensitivity sacrificial specimen of item (1) is a small sized fatigue coupon which is designed so that fatigue damage may be produced in the specimen sufficiently earlier when it is secured to the structural member. In this study, a coupon specimen which is secured onto the structural member by using adhesive agent is developed. The … More purpose is to estimate the level of long-term stress distribution working on structural member. From the fatigue tests using specimens and using a real container ship, it is found that the sacrificial specimens can predict the long-term stress of actual members.Stress sensor using piezoelectric element of item (2) is developed to monitor the stress history of structural member. The sensor is a rectangular box(90mmX60mmX25mm) made of thin aluminum plate, in which piezoelectric element, electric circuit, including integrating circuit, button type battery, make and break swich, stress level meter using LED and stress level cross counter are facilitated. The stress level meter can light on and off different color diodes according to the change of stress level. The stress level cross counter can display the number of cycles which exceeds a specific stress level during the monitoring period. The sensor is bonded onto the structural number by using adhesive agent. Through the several tests in the laboratory, it is found that the sensor can monitor the stress history of structures. Less