Fatigue Life Estimation of Offshore Structures Under Variable Loads.

本研究项目由两个主题组成。在第一个题目“多缺口试件疲劳试验及其可靠性分析”中，提出了一种多缺口试件的疲劳试验方法，目的是通过少量的疲劳试验来估计疲劳裂纹萌生寿命的分布函数。重点是有效利用一个试件提供的疲劳数据，减少疲劳试验所需的试件数量。试验结果表明，两个或三个多缺口试件足以确定实际水平的裂纹萌生寿命分布函数。在第二个题为在役检验对结构疲劳损伤可靠性退化的影响中，提出了一种通过定期在役检验来估计结构构件可靠性的一般方法。选取疲劳裂纹萌生前后存在失效可能性的TLP筋连接构件，进行了可靠性检测分析。讨论了构件的疲劳性能、构件的故障率、裂纹的可检验性和起裂裂纹的形状等因素对结构可靠性的影响。

This research project consists of two topics. In the first topic titled "Fatigue Test Using Multi-Notched Specimen and Its Reliablilty Analysis", a fatigue testing method using a multi-notched test specimen are presented for the purpose of estimating the distribution function of fatigue crack initiation life by a small number of fatigue tests. Emphasis is put on the effective use of the fatigue data provided by one test specimen and to decrease the number of specimens required in the fatigue tests. The experimental results indicate that two or three multi-notched specimens are enough to determine the distribution function of crack initiation life of practical level.In the second topic titled "Effect of In-Service Inspection on the Reliability Degradation of Structrues Due to Fatigue Damage", a general method for estimating the reliability of structural member through periodic in-service inspections is developed. Choosing a connecting component of TLP tendon, which has a possibility of failure before and after the fatigue crack initiation, reliability analysis of inspections are carried out. And the effects of fatigue properties of member, the failure rate of member, detectability of a crack by inspection and the shape of initiated crack on the structural reliabilities are discussed.