A geometric method of fatigue SCF and fracture SIF assessment

• Main Author: Lou, Benqiang
• Published: University of Strathclyde 2013
• Subjects: 623.8
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.576441

In modern marine structural design, the fatigue life and fracture prediction of local connection details of the vessel is necessary. The traditional empirical rules or numerical work has considerably advanced the qualitative and quantitative understanding of fatigue and fracture analysis. Compared with the existing methods, this thesis explores a novel geometric methodology to evaluate the stress intensity and stress concentration factors (SIF and SCF). The background and special theory was developed to give: 1. A better understanding of the singularities that commonly occur in sharp corners in ship connection details; 2. A quicker method for fatigue life estimation than present methods based on finite element analysis and/or detail classes. 3. A prediction of the stress fields so that more appropriate and reliable finite element meshes can be selected When dealing with the influence of each connection detail, a "Length Scale" estimated from the dimensions of the connection detail. This Length Scale can be converted into a Hot Spot Stress Concentration Factor for SN based fatigue calculations or used with (often simply added to) the real crack length to determine, in conjunction with a constant Y value (commonly 1.1) a Stress Intensity Factor for linear elastic fracture mechanics crack growth calculations. The method is useful both for assessment of existing structures and for design application. The thesis includes a comparison of the results from the application of this new methodology and existing fatigue analysis guidance. Within the thesis the methodology is described together with relevant conclusions.