Menu

Discussion Forum

New Discussion
Filtrer

Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.

Number of Cycle to Failure (Fatigue Analysis)

Posted 25 avr. 2022, 04:40 UTC−4 Structural & Acoustics, Acoustics & Vibrations, Structural Mechanics Version 6.0 2 Replies

Shivaksh Rohatgi
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Hi all, I am doing a Fatigue stress based analysis of a tuned mass dampener with the end goal of obtaining S-N Curve (or Wöhler curve) to determine the relation between Stress and number of cycles to failure for my geometry. I used the findley's criterion and successfully coputed fatigue usage factor but not able to figure out the way to obtain number of cycles to failure.

Can someone help me by telling if (and how) I can get this in Comsol or am I supposed to use other software for this purpose?

Thank you.

2 Replies Last Post 27 avr. 2022, 09:18 UTC−4
Mats Danielsson COMSOL Employee

Please login with a confirmed email address before reporting spam

Posted: 3 years ago 27 avr. 2022, 05:03 UTC−4

Hello.

The Findley criterion applies to the fatigue limit of the material, where the fatigue usage factor that is computed suggests failure if it exceeds one, etc. Now, if you want to use the Findley criterion for finite life computations, using an S-N curve, it is doable, but you would currently need to do it manually. The criterion computes a measure of stress deemed the most critical. After performing the fatigue computation, you could then use this stress in an S-N curve to get the number of cycles. Note, however, that in order to do this, you would need to shift the S-N curve, depending on the R value that it represents. If you are then able to express the inverse of this shifted S-N curve, N(S), you immediately get the number of cycles. Otherwise, you would need to solve an equation to get the number of cycles.

Mats

Hello. The Findley criterion applies to the fatigue limit of the material, where the fatigue usage factor that is computed suggests failure if it exceeds one, etc. Now, if you want to use the Findley criterion for finite life computations, using an S-N curve, it is doable, but you would currently need to do it manually. The criterion computes a measure of stress deemed the most critical. After performing the fatigue computation, you could then use this stress in an S-N curve to get the number of cycles. Note, however, that in order to do this, you would need to shift the S-N curve, depending on the R value that it represents. If you are then able to express the inverse of this shifted S-N curve, N(S), you immediately get the number of cycles. Otherwise, you would need to solve an equation to get the number of cycles. Mats
Shivaksh Rohatgi
Send Private Message Flag post as spam

Please login with a confirmed email address before reporting spam

Posted: 3 years ago 27 avr. 2022, 09:18 UTC−4
Updated: 3 years ago 27 avr. 2022, 09:19 UTC−4

Hello.

The Findley criterion applies to the fatigue limit of the material, where the fatigue usage factor that is computed suggests failure if it exceeds one, etc. Now, if you want to use the Findley criterion for finite life computations, using an S-N curve, it is doable, but you would currently need to do it manually. The criterion computes a measure of stress deemed the most critical. After performing the fatigue computation, you could then use this stress in an S-N curve to get the number of cycles. Note, however, that in order to do this, you would need to shift the S-N curve, depending on the R value that it represents. If you are then able to express the inverse of this shifted S-N curve, N(S), you immediately get the number of cycles. Otherwise, you would need to solve an equation to get the number of cycles.

Mats

Thank you Mats. I was able to get number of cycles for a range of load (using parametric sweep), but to plot them in an S-N curve I need stress data from the result of Study 1 (Stationary analysis) and number of cycle data from Study 2 (Fatigue analysis). Is it possible to plot this graph in Comsol or the only way to do it is to export data and use other plotting software to do that. I have attached my model builder sceenshot for reference ?

>Hello. > >The Findley criterion applies to the fatigue limit of the material, where the fatigue usage factor that is computed suggests failure if it exceeds one, etc. Now, if you want to use the Findley criterion for finite life computations, using an S-N curve, it is doable, but you would currently need to do it manually. The criterion computes a measure of stress deemed the most critical. After performing the fatigue computation, you could then use this stress in an S-N curve to get the number of cycles. Note, however, that in order to do this, you would need to shift the S-N curve, depending on the R value that it represents. If you are then able to express the inverse of this shifted S-N curve, N(S), you immediately get the number of cycles. Otherwise, you would need to solve an equation to get the number of cycles. > > >Mats Thank you Mats. I was able to get number of cycles for a range of load (using parametric sweep), but to plot them in an S-N curve I need stress data from the result of Study 1 (Stationary analysis) and number of cycle data from Study 2 (Fatigue analysis). Is it possible to plot this graph in Comsol or the only way to do it is to export data and use other plotting software to do that. I have attached my model builder sceenshot for reference ?

Attachments:

Note that while COMSOL employees may participate in the discussion forum, COMSOL® software users who are on-subscription should submit their questions via the Support Center for a more comprehensive response from the Technical Support team.

Suggested Content