- #1

FEAnalyst

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- TL;DR Summary
- Is it possible to calculate the fatigue life of a simple beam analytically?

Hi,

some time ago I wondered if it's possible to calculate fatigue life (number of cycles to failure) for complex models analytically, based on static FEA results: https://www.physicsforums.com/threa...culations-based-on-static-fea-results.994264/

Unfortunately, it seems that it's not doable. However, now I would like to perform such calculations for a simple case of a beam subjected to bending. Let's assume that the beam is simply-supported and has uniformly distributed load (UDL) acting on it. Let's assume that the beam is 1 m long, has square cross-section (40x40 mm) and is made of steel. Force resultant of applied UDL is 8000 N. Thus the maximum stress is around 94 MPa. I used bilinear stress-life curve approximation with 2 data points: transition (stress: 200 MPa, life: 1000 cycles) and endurance (stress: 75 MPa, life: 100000 cycles). Direct reading of fatigue life for stress of 93.75 MPa gives the following result (interpolated linearly): 85150 cycles to failure.

I performed a numerical analysis in SolidWorks Simulation to check this. Static stress result is correct but the result of fatigue simulation is around 40000 cycles to failure. What may cause the difference ? Does it mean that it's not possible to calculate faitgue life even in such a simple case ? Or maybe I should use different approach than simply reading from stress-life curve ? I'll just add that mean stress effect wasn't included here (because I assumed fully-reversed loading) and that I enabled fatigue calculation based on von Mises stress (instead of stress intensity) in SolidWorks Simulation. I also specified 1000000 as the number of cycles for this study.

some time ago I wondered if it's possible to calculate fatigue life (number of cycles to failure) for complex models analytically, based on static FEA results: https://www.physicsforums.com/threa...culations-based-on-static-fea-results.994264/

Unfortunately, it seems that it's not doable. However, now I would like to perform such calculations for a simple case of a beam subjected to bending. Let's assume that the beam is simply-supported and has uniformly distributed load (UDL) acting on it. Let's assume that the beam is 1 m long, has square cross-section (40x40 mm) and is made of steel. Force resultant of applied UDL is 8000 N. Thus the maximum stress is around 94 MPa. I used bilinear stress-life curve approximation with 2 data points: transition (stress: 200 MPa, life: 1000 cycles) and endurance (stress: 75 MPa, life: 100000 cycles). Direct reading of fatigue life for stress of 93.75 MPa gives the following result (interpolated linearly): 85150 cycles to failure.

I performed a numerical analysis in SolidWorks Simulation to check this. Static stress result is correct but the result of fatigue simulation is around 40000 cycles to failure. What may cause the difference ? Does it mean that it's not possible to calculate faitgue life even in such a simple case ? Or maybe I should use different approach than simply reading from stress-life curve ? I'll just add that mean stress effect wasn't included here (because I assumed fully-reversed loading) and that I enabled fatigue calculation based on von Mises stress (instead of stress intensity) in SolidWorks Simulation. I also specified 1000000 as the number of cycles for this study.