Fatigue Calculation for Structures - reg 1

[Sivadas5791]

How to carry out fatigue calculation for locomotive car body structures ? Which method is preferable Equivalent stress approach or Linear damage calculation ? The method has to be inline with eurocode design guidelines . I have carried out the fatigue load case with +0.15 g and -0.15 g, how do i proceed next ?

 

[karachun]

First you can check eurocode design guidelines to see what methods they use.

 

[rb1957]

what's the endurance limit of your steel ? I mean, you want infinite life, yes? So endurance limit equals either
a) 1.15g (the maximum stress of your fatigue cycle
b) 0.15g (the alternating stress of your fatigue cycle)
The R of your fatigue cycle (= min/max) is very high (about 0.74) which works in your favour.

For a precise number …
1) how many cycles per hour ?
2) how many hours in service ?
3) what safe life factor ? (3, 4, 5, 10?)

I understand that train wheels are monitored/inspected for fatigue damage (temperature or ringing sound) … why should your body be more sensitive to fatigue

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

 

[Sivadas5791]

@rb1957 yes the car body is also analyzed for fatigue . Its for 5*10^6 Cycles ,after running the model for +/- 0.15 g.How to consider the stress range ? how do i calculate fatigue for welds? The analysis has to meet eurocode 9 guidelines.

 

[rb1957]

"Its for 5*10^6 Cycles" … factored safe life, mean life, design (unfactored) life ?

"after running the model for +/- 0.15 g" … about 1g right ? so a load cycle of 0.85g to 1.15g …

"How to consider the stress range ?" … that'd be on a case by case basis … depending on the detail you're analyzing, what doe the FEM tell you ? I'd typically cut fatigue stress at zero, but I think you mechanical guys use the compression part of the cycle. I'm guessing you need something like a Goodman diagram or some other fatigue analysis S/N diagram.

"how do i calculate fatigue for welds? The analysis has to meet eurocode 9 guidelines." … not a clue !

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