Fatigue Strength of Ship Structural Details Using Notch Stress Intensity Factors

Field of Research: Fatigue Strength; Ship Structural Design

Duration: 01.04.2010 – 31.10.2014

Project leader: Prof. Dr.-Ing. W. Fricke

Funded by: TUHH Pool

Summary:

More and more, engineers apply finite-element-analyses (FEA) in combination with simplified methods for fatigue assessment to design structural components – in ship building industry mainly the concept of structural hot-spot stress using coarse numerical models with shell elements. Nevertheless, an economic design calls for a satisfyingly exact assessment of lifecycle as well as simple application. Moreover, high flexibility is necessary with respect to different geometries of weld joints and crack locations. In case of some typical structural details of ships the hot-spot stress method has reached its limit.

An interesting alternative which shows great promise assesses fatigue strength on basis of notch stress intensity factors (N-SIF) and the averaged strain energy density (SED). In this relatively new approach local notches which are caused by fabrication as well as welding processes are reduced to sharply shaped V-notches. The fatigue behavior of these is described by one uniform S-N curve showing narrow scatter. In addition, a relative coarse mesh which could be generated with less effort is suitable FEA despite of the focused view on a highly local position. Size effects and links to other approved concepts on fatigue assessment are included as well.

The research project has the aim to introduce the recent method based on the averaged SED in practical shipbuilding design process by means of different – simple and complex – welding details. Thereby, varying constructions of finished research projects are investigated numerically and references with respect to advantageous modeling technique and estimation automation are derived. Furthermore, the underlying assumptions and influence parameter (notch opening angle as well as yield strength and fatigue behavior of material) are validated by performing fatigue tests of flushed grinded butt welds which are prepared with a defined notch in the heat affected zone.

Persons: C. Fischer

Papers:

Feltz, O.; Fischer, C. and Fricke, W..Fatigue Assessment of Weld Toe and Root Cracks with the Notch Stress Intensity and Crack Propagation Approach. Proc. of ,11th Intl. Symp. on Practical Design of Ships and other Floating Structures, COPPE/UFR, Rio de Janeiro; 2010

Feltz, O.; Fischer, C.; Fricke, W. and Larrrazin, P.:Application of the Notch Stress Intensity and Crack Propagation Approaches to Weld Toe and Root Fatigue. IIW-Doc. XIII-2337-10/XV-1354-10, Int. Inst. of Welding, 2010

Düster, A.; Fischer, C. and Fricke, W.: Beurteilung der Schwingfestigkeit von Schweißverbindungen auf Basis der lokalen Formänderungsenergiedichte. Jahrbuch der Schiffbautechnischen Gesellschaft, 105. Bd., Schiffahrts-Verlag „Hansa“ C. Schroeder & Co., Hamburg (erscheint 2012)

Fischer, C.; Düster, A. and Fricke, W.: Different Finite Element Refinement Strategies for the Computations of the Strain Energy Density in a Welded Joint. In: Advances in Marine Structures (Ed. Guedes Soares & Fricke), Taylor & Francis, London, 2011

Fischer, C.; Feltz, O.; Fricke, W. and Lazzarin, W.: Application of the Notch Stress Intensity and Crack Propagation Approaches to Weld Toe and Root Fatigue. Welding in the World 55, 7/8, 2011, pp. 30-39

Fischer, C.; Fricke, W. and Rizzo, C.M.: N-SIF based fatigue approaches of hopper knuckle details. In: Sustainable Maritime Transportation and Exploitation of Sea Resources, Rizzuto & Guedes (Eds.), Taylor & Francis Group, London 2011

Fischer, C.; Fricke, W. and Rizzo, C.M.: Bewertung der Schwingfestigkeit auf Basis von Kerbspannungsintensitäten am Beispiel von geschweißten Knicken im Schiffbau. In: DVS-Berichte Bd. 275 ‚Große Schweißtechnische Tagung 2011‘, DVS-Media GmbH, Düsseldorf, 2011

Rizzo, C.M.; Fischer, C.: Application of advanced notch stress approaches to assess fatigue strength of ship structural details: applications and comparisons, Schriftenreihe Schiffbau 662, Technische Universität Hamburg-Harburg, Hamburg, 2012

C.M. Rizzo, C. Fischer: Application of advanced notch stress approaches to assess fatigue strength of ship structural details: analysis of tests and evaluation of approaches for complex geometries. Schriftenreihe Schiffbau 674, Technische Universität Hamburg-Harburg, Hamburg, Germany, 2014.