How to use the fatigue strength reduction factor?
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The JB4732 fatigue analysis mentions the fatigue strength reduction factors for fillet welds and studs – how are these factors used? For studs, I can understand it as the average tensile stress of the bolt, multiplied by this coefficient, to obtain the stress required for fatigue calculations. But what about fillet welds? How should those be handled?
As I understand it, it involves calculating the membrane stress on the compressed elements at the fillet weld, then multiplying that value by 4.0; this resulting value is used to assess the fatigue of the fillet weld. For example, the weld area between the saddle pad and the cylinder.
This coefficient is very large; if it is taken into account, the requirement cannot be met. It is recommended to use the Asme method, as it takes grinding and non-destructive testing into account, allowing the coefficient to be set at no more than 1.5
It can only be judged as 4732; the fillet welds indeed do not meet the requirements. We basically do not use fillet weld structures for the pressure-bearing components of our fatigue testing equipment.
The stud strength should be calculated as membrane stress plus bending stress, multiplied by the fatigue strength reduction factor; the fatigue strength reduction factor at the corners of fillet welds is 2. The values to be used depend on the interpretation of the structure in accordance with ASME-III NB sections, and we are not clear about how to interpret our 4732 standard