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VIDEO: Fatigue of Welded Structures
Wednesday, 23 September 2009

MoreVision has developed a number of programs to post-process finite element results, calculate fatigue damage and to plot damage directly onto the FE mesh. The assessments cover code of practices used in many countries (UK - BS7608, US - AISC LRFD,  France -UIC 515-4 Goodman Diagram, German DIN 15 018, Swedish Volvo standards)

Fracture Mechanics If a component is subject to repeated applications of structural loading then it will be susceptible to fatigue failure. Stresses act on small flaws inherent in the material causing then to grow until they break. Two approaches can be employed to assess this situation:
    • Fatigue Life Assessment.
    • Fracture Mechanics Approach.
Using stress information derived from an ANSYS structural analysis MoreVision have developed custom programs to assess fatigue life or to study crack growth.

Our library of programs includes methods of assessment used in various countries following a number of codes:
Fatigue Life Assessment
    • UK - BS7608 (fabricated steel), BS8118 (aluminium), BS5400 (bridges), BS2573 (cranes).
    • US - AISC LRFD.
    • France - UIC 515-4 Goodman Diagram (railway).
    • German DIN 15 018 (cranes).
    • Swedish Volvo standards (automotive, construction equipment).
Fracture Mechanics Approach
    • UK - PD6493 (fracture).

The fatigue life of a welded structure it totally dependant upon the choice of welded detail. In the following examples the detail on the left hand side of the page is improved by adopting the detail on the right hand side. Just three examples are given though there are generally many ways of optimising a fabricated structure.

1) Weld reinforcement and weld toe re- profiling

The fatigue life of this butt weld is improved by grinding the weld reinforcement flush with the parent plate. This reduces the stress concentration at the weld toe. Paradoxically it could be further enhanced if the weld toes are dressed back 1 to 2mm below the thickness of the parent plate! The benefit from the removal of poor quality material at weld toes which contains fatigue prone inherent flaws outweighs the slight increase in stress due to loss of net section.

2) Removal of weld stop starts


The presence of stop start defects in a weld will reduce the fatigue life of a weld.

3) Do not weld on plate edges


Welds on the edge of a stressed plate have a lower fatigue life than welds which stop 10mm short of the edge.

 

Consultancy Projects - Fatigue Analysis Of Welded structures


Finite element stress analysis.
Finite element stress analysis.

Understand fatigue classification of welds.
Understand fatigue classification of welds.

Understand how to select appropriate stress from finite element model for fatigue assessment.
Understand how to select appropriate stress from finite element model for fatigue assessment.

Software developed by MoreVision to take benefit from fatigue enhancement methods (like toe grinding, TIG dressing and stress relieving).
Software developed by MoreVision to take benefit from fatigue enhancement methods (like toe grinding, TIG dressing and stress relieving).

View fatigue classification directly on finite element model.
View fatigue classification directly on finite element model.

View damage directly on finite element model.
View damage directly on finite element model.

Export results to spreadsheet for detailed analysis and verification.
Export results to spreadsheet for detailed analysis and verification.

Fatigue assessment of rollercoasters.
Fatigue assessment of rollercoasters.

Fatigue assessment of railway bodyshells and running gear.
Fatigue assessment of railway bodyshells and running gear.

 

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