Crack Propagation Analysis And Fracture Assessment Of Marine High Tensile Steel Plate Of Container Ships

Fatigue is one of the main damage modes of ship and ocean engineering structures.The application of high tensile steel makes the fatigue problem in ship hull moresevere. For large container ships whose decks are constructed with thick high tensilesteel plates, it is necessary to perform studies on safety life assessment of the partswith welding defects in thick high tensile steel plates. The main works of this paperare as follows:1) The models of long-term response stress distribution of wave induced fatigueload are introduced, along with methods to determine the long-term stress rangedistribution, including simplified method, spectrum analysis method and design wavemethod. The simplified methods respectively based on DNV, CCS and JTP-CSR rulesare compared and used to determine the long-term stress range distribution of a40000T oil tanker. The calculation results of different rules are quite different fromeach other.2) Fatigue assessment methods are introduced, including cumulative damagemethod and fracture mechanics method. The latter can better reflect the nature ofstructure fatigue, and explain some fatigue phenomena. Especially for welded jointswith lots of initial flaws, fracture mechanics method is more appropriate.3) In this paper, the fatigue loading spectrum was generated from the long-termdistribution which obeys two-parameter Weibull distribution, and the unique crackgrowth rate model was adopted to predict the crack size at any given time. Combiningthe predicted crack size, the calculation of stress intensity factor and reference stressand Failure Assessment Diagram (FAD), a procedure to assess the safety life of acracked thick high tensile steel plate was put forward.4) The safety life assessment of thick high tensile steel deck plate with anembedded crack in a container ship was performed by coding a calculation program.In addition, the influence of fatigue loading spectrum on damage tolerance and fatiguelife was analyzed. The calculation results indicate that the length of fatigue loadrepetition period as well as the value of shape parameter of Weibull distribution willgreatly affect the fatigue safety life.