## How does a Fatigue analysis software use a FEM model in life estimation calculations?

## How does a Fatigue analysis software use a FEM model in life estimation calculations?

(OP)

Hi All

I just need to know how does a fatigue analysis software use the FEM model we load in it to calculate the life, cause i don't find it on manuals

I just need to know how does a fatigue analysis software use the FEM model we load in it to calculate the life, cause i don't find it on manuals

## RE: How does a Fatigue analysis software use a FEM model in life estimation calculations?

## RE: How does a Fatigue analysis software use a FEM model in life estimation calculations?

another day in paradise, or is paradise one day closer ?

## RE: How does a Fatigue analysis software use a FEM model in life estimation calculations?

1. Determine the no. of load input points or channels.

2. Collect the load histories for these channels.

3. Perform unit load analysis in FEA for each channel.

4. Software then determines simultaneous max and mins

across all channels. This results in a reduced

set of loads but hopefully will contain all significant

events.

5. Using the simul. max mins and the unit loads applies superposition

to determine the x,y & maybe Z elastic stress histories for

each element.

6. determine the critical stress direction (max principal histograms,

2D or 3D ) for each element. Then calculate the normal stress

history in this critical direction for each element.

7. Rainflow cycle count this normal stress for each element.

8. Applying a Neuber type plasticity correction to determine element's

elastic and plastic closed stress-strain hysteresis loops.

9. Do a Palmgren-Miner damage estimate for each element.

10. Select a user determined number of max damaged elements. Number

depends on computer available.

11. Repeat steps 5 to 10 for all the max damaged elements using the

full load history of each channel, multiplied by the unit loads,

and superimposed.

12. Take life predictions and adjust by a user determined (from

experience) safety factor.