Study on the fatigue strength of Ships and Offshore Structures under Variable Amplitude Loading Conditions

这项研究的目的提出了一个实用的Fatigue-strength diagram，用于设计船舶和离岸结构的实用性-strength.由于其目的，其Fatigue-strength characteristic characteristic in the variable amplitude loading conditions of structure of structures， corrosion environmental conditions， and the variation on work need to be taken to consideration.我们在开发的顺序中进行了调查，并在crack propagation behavior中进行了研究。对裂缝打开和关闭操作的测量，对焊接连接中使用的测试片段的疲劳测试，以及裂缝传播分析程序的开发。使用开发的程序创建了一个致命的强度的诊断程序，获得的结果将按以下方式进行。Kop预测公式的提出，其中可以用于裂缝传播分析。两种或更多的配方化，其中一些可以用于裂缝传播分析，被提议围绕表面裂缝的干扰影响。Crack传播分析程序，其中一个程序可以将变量放大器加载、多表面Crack和Corrosion环境条件纳入其中。通过与本研究和其他研究人员的可变抽样加载测试结果进行比较，该测试结果被开发的程序所批准。Crack传播分析的初始裂纹设置方法已经提出。根据裂纹传播分析的基础，一个硬度-强度图可以被用于初始设计的建议。由于初始裂纹的变化而改变的命运强度是明确的。

The purpose of this research is proposing the practical fatigue-strength diagram for designing of ships and offshore structures.For that purpose, the fatigue-strength characteristic under the variable amplitude loading conditions of structure material, corrosion environmental conditions, and the variation on works need to be taken into consideration.We inquired in the order of development of examination of a crack propagation behavior, measurement of a crack opening-and-closing action, the fatigue test that used the test pieces of a welded joint, and a development of crack propagation analysis program. The fatigue-strength diagrams ware created using the developed program.The obtained results are as follows.・Proposed of Kop presumption formula which can be used for crack propagation analysis.・Two or more formulization which can be used for crack propagation analysis was proposed about the interference influence of a surface crack.・The crack propagation analysis program which can take into consideration of variable amplitude loading, multiple surface crack, and corrosion environmental conditions was developed.・By comparison with the variable amplitude loading test result by this research and other researchers, it checked that the analysis result by the developed program was appropriate.・The initial crack setting-up method for crack propagation analysis was proposed.・On the basis of crack propagation analysis, the fatigue-strength diagram which can be used for an initial design was proposed.・Variation in the fatigue strength by change of initial cracks was clarified.