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Cumulative Damage Calculations With The Proposed New Fatigue Design Rules

TWI Industrial Member Report Summary 4/1976

By T R Gurney


In the new fatigue design rules for welded joints the S-N curves for most joints will be parallel straight lines when plotted as Log stress v. Log cycles, and the cut-off level for cumulative damage calculations will occur at a constant life. It is shown that, on account of these features, it will in many cases only be necessary to carry out a single cumulative damage summation and that it will then be possible to deduce the correct design stress by multiplying by suitable factors. In the same way it will be possible to define design stresses for other joint classes, other probabilities of failure and other spectrum lengths. Thus calculation procedures will be considerably simplified.