Through-life hybrid fatigue assessment of naval ships

Abstract

When a ship enters service it has an implied or calculated design fatigue life. Factors including construction quality, loads, material performance, and operational profile are assumed. However, these factors vary through life. Failure of structural items due to fatigue cracking can lead to increased cost of ownership and reduced capability. Therefore, to allow informed decision-making regarding fleet availability and economy, it is necessary to monitor the variables that influence a ship's fatigue life. This paper presents a new method whereby in-service data, fleet maintenance reports, and Finite Element Analysis are incorporated to predict ongoing fatigue life and hence support the management of the remaining service life of a ship. The method is applied to a naval High Speed Light Craft to demonstrate its merit. The fatigue lives of different welded details are predicted using a practical implementation of the S-N curve approach, employed with strain and operational data acquired from an on-board hull monitoring system. The proposed method is efficient because it is properly linked to stress analysis, inherently includes the influence of the operational profile, and is a balance between accuracy and effort.

Numerical Prediction of Cavitation Fatigue Life and Hydrodynamic Performance of Marine Propellers

“…The specification lacks a corresponding fatigue analysis formula. Structural fatigue strength analysis methods include the nominal stress method [18], the junction stress method [19], the local stress method [20], and the fracture mechanics method [21]. The nominal stress method is primarily used in engineering to estimate the effective fatigue life with Finite Element Method (FEM) based on the material's S-N curves and fatigue damage accumulation theory [22].…”