The current procedures of fatigue design of ship structural components via application of S-N diagrams based on the test results of typical, simple welded joints are not complete and may need an adjustment. The main base for discrepancies of actual and S-N-modeled fatigue behavior of structures is an approximation following the principles of identity of fatigue damage in baseline specimens and in the actual conditions of structural details. Some of the principal sources for discrepancies are the following: (1) in ship hull structures the fatigue process is mostly the displacement-controlled whereas the laboratory testing of welds occurs under the load-control, (2) the laboratory specimens which are the bases for design S-N diagrams are usually tested until the complete failure and development of fatigue process depends mostly on the compatibility of test-pieces whereas in actual structures the compatibility may not be affected, etc. The identity of fatigue processes in both hull details and specimens therefore may be restricted to the initial phase of the process including fatigue crack initiation and early propagation, mostly within the stress concentration zone since the local conditions are assessed in fatigue analysis and design. A procedure of adjustment of design S-N curves is developed which retains the current format of fatigue design and takes into consideration the possible mismatch in conditions for fatigue damage between laboratory specimens and structural details. The method is based on application of the strain-controlled approach to both the specimen and the detail.
With S. V. Petinov and A. K. Thayamballi, "The Similitude of Fatigue Damage Principle: Application in S-N Curve-Based Fatigue Design," Proceedings of the Symposium - Fatigue Design '98, Espoo, Finland, 1998.