Understanding Fatigue Simulations
. . or any other method that I’m more familiar with? I need to justify this to my customer/ to my boss/ for my own understanding. This is a question I’m often faced with when proposing fatigue simulation as a viable option for calculating fatigue life as part of a larger project.
The truth is, it depends. I know this isn’t the clear-cut answer that you were hoping for, but in reality the answers to non-trivial questions generally aren’t as definitive as everyone would like, especially when dealing with FEA.
Put simply, the reason that the two aren’t comparable is because fatigue simulation encompasses its own methodology whereas code assessment is its own, separate methodology. In this sense, the difference between the two is the same as comparing hand calculations to structural simulations. Yes, they both intend to achieve the same result, but they do so by different means.
The reason that they are comparable is that fatigue simulations – in particular fe-safe – include all the same algorithms that code assessments do. Whether your preferred code for fatigue assessment is ASME VIII div 3, API 579-1 or any other code, every fatigue damage equation stated within these codes is incorporated within the fe-safe solver and available for the user to select.
Returning to the hand calc vs simulation analogy, it is widely accepted that hand calcs are fairly limited in their application due to their simplicity, whereas structural simulation methods are more robust and allow for a greater complexity in geometry, loading and material definition. The same is still true for fatigue simulations vs code assessments, but this isn’t as readily accepted. Code assessments still have their limitations such as the practical limit of failure locations the user is able to assess or how prone the method is to human error – issues which are not inherent in the fatigue simulation process.
It does seem ironic that structural simulation is pretty standard in a design process but extrapolating that methodology to include the simulation of fatigue lives is rejected, and instead the user resorts to manual fatigue calculation methods based upon the simulated stress results.
Fortunately fatigue analysis is becoming more commonplace but there’s still some way to go before it is as readily accepted as structural simulation.
