Study on Fatigue Strength Evaluation of Ship Structural Members in The Ocean Going

为了发展一种更可靠、更精确的船舶结构构件疲劳设计方法，提出了一种新型的疲劳设计图。这些图表是通过以下三个过程得出的：（1）使用疲劳裂纹扩展分析作为疲劳强度评估的基础，（2）实施作者的新风暴模型，用于波浪载荷引起的应力发生的时间历程，（3）采用新的航行模型代替全航向模型。这些图表是三维的，由以下三个参数组成：1）外部载荷中的最大应力幅，2）应力集中系数和3）裂纹结构构件中的疲劳裂纹长度。它们可用于任何疲劳寿命，并可用于初始疲劳设计，而不是当前的疲劳设计规范。他们还预测剩余疲劳寿命在开裂的结构构件时，疲劳裂纹后发现一定的服务期。

In order to develop a more reliable and accurate fatigue design method for ship structural members, a new type of fatigue design chart is proposed. These charts are derived by the following three procedures : (1) use of fatigue crack growth analysis as the basis for fatigue strength evaluation, (2) implementation of the authors' new storm model for the time history of stress occurrence induced by wave load and (3) incorporation of a new sailing model instead of the all headings model. The charts are 3-dimensional and are composed of the following three parameters : 1) maximum stress amplitude in the external load, 2) stress concentration factor and 3) fatigue crack length in cracked structural members. They can be prepared for any fatigue life and be used for initial fatigue design instead of the current fatigue design code. They also predict the residual fatigue life in cracked structural members when fatigue cracks are found after a certain service period.