TWI Frequently asked questions
In the UK, you should consult BS7608:1993 'Code of practice for fatigue design and assessment of steel structures' which provides guidance on allowable cyclic stresses for welded joints. Similar rules will be found in BS8118 Part 11991 'Structural use of aluminium - Code of practice for design' for joints in aluminium alloys. The allowable stress is strongly dependent on joint geometry; for example, fillet welds have a lower fatigue strength than butt welds. Thestandards provide a series of sketches of typical joints showing potential failure sites, and give the fatigue performance for each in terms of an S-N curve (where S is the allowable nominal cyclic stress range and N is the fatiguedesign life in cycles). Similar data are published by other national standards organisations.
See also 'Fatigue Strength of Welded Structures', by S J Maddox, 2nd Edition, Abington Publishing, 1991. (ISBN 1 85573 013 8)
Copyright by TWI, 1999
