Fatigue Damage in Aluminium Welds.xls

Calculate fatigue damage in an aluminium weld subjected to constant amplitude loading and variable amplitude loading according to the rules of BS8118. This calculation requires the XLC addin to be installed.

Calculation Reference

Aluminium Design and Construction - Dwight

Fatigue of Welded Structures - Gurney

Calculate fatigue damage in an aluminium weld subjected to constant amplitude and variable amplitude loading according to the rules of BS8118:

Constant Amplitude Loading

• Determine the stress range (DS) that the weld is subjected to from the loading
• Lookup the fatigue strength curve (S-N curve) for the appropriate weld detail category at 2x106 cycles
• Calculate the damage fraction (D) using Miner's rule: D = n/N Where: n = number of applied cycles N = number of allowed cycles from the S-N curve for that stress range

Variable Amplitude Loading

• Divide the load history into a series of constant amplitude load blocks, each with its own stress range
• Determine the stress range for each load block
• Lookup the number of allowed cycles (N) for each stress range from the S-N curve
• Sum the damage fractions for each load block to determine the total damage fraction:
  D = SUM (ni/Ni) Where:
  ni = number of applied cycles in load block i Ni = number of allowed cycles for stress range in block i
• BS8118 provides other rules relating to load sequence effects, interaction effects between constant amplitude and variable amplitude loading, and treating the varying load as equivalent constant amplitude stress ranges.

The total damage fraction D should be ? 1.0 for fatigue failure not to occur. Higher damage fraction means earlier failure from fatigue.