Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


RE: How can Rupture Allowable Stress be Less than Creep Allowable?

RE: How can Rupture Allowable Stress be Less than Creep Allowable?

RE: How can Rupture Allowable Stress be Less than Creep Allowable?

Additional info for (closed) thread367-305865: How can Rupture Allowable Stress be Less than Creep Allowable?
Original Poster: PSSC

A likely reason for the discrepancy/confusion could be that rupture tests and creep tests are carried out in a fundamentally different way-- namely, the strain rates employed. Creep testing is done with sensitive strain equipment because we are explicitly interested in the strain rate throughout the testing, and these tests are long (up to 10k to 30k hours). Rupture testing is done at much higher strain rates (shorter tests-- ~1k hours) with less sensitive strain equipment. The devil in the detail is that some of the defined parameters that illustrate the process depend on strain rate. So, when we extrapolate the data from rupture tests to, say, 10k hours, the illustrative parameters are not comparable to those borne of the creep test conditions. Furthermore, some extrapolations can be up to 30% different from experimental data, and there are some mechanical phenomena that occur only under long-life conditions (e.g. after 40k+ hours). Therefore, it is important to bear this in mind when considering the loading profile for a design.

It might be important to find the strain rates used in the rupture experiments.
That being said, according to an article by Euro Inox on BSSA's website:
"It is usually satisfactory if creep does not exceed 1% deformation in 10,000 hours.... A design stress figure commonly used for uniformly-heated parts not subjected to thermal or mechanical shock is 50% of the stress to produce 1% creep in 10K hours. However, this should be used carefully and verified with the supplier. A[nother] common criterion is for the load to cause failure at 100K hours, with an added safety factor of 1.5 (see the ASME code, for example)." (article link, page 8)

more detail on creep and rupture differences: http://www.tech.plym.ac.uk/sme/mats340/cpintro.pdf


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close