×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

ASME viii div 2 fatigue failure probability?

ASME viii div 2 fatigue failure probability?

ASME viii div 2 fatigue failure probability?

(OP)
Where in ASME viii div 2 can I find for what failure probability the S-N curves in Annex 3-F are specified? Can those S-N curves be modified for a different failure probability?

RE: ASME viii div 2 fatigue failure probability?

For non-welded (smooth bar) curves, the "failure probability" is not provided and the curves may not be modified for use in constructing ASME pressure vessels.

The welded curves for use with the Structural Stress Method do have confidence intervals about the mean presented. The engineer is directed to use the -3σ curve unless otherwise negotiated with the user (and likely the jurisdiction).

RE: ASME viii div 2 fatigue failure probability?

(OP)
Thanks TGS4 for a prompt, informative reply. I have a case with a customer requesting us to use this pressure vessel norm, but the application is not a pressure vessel. I argue that this norm is not suitable for regular machine components (forged, machined steel), where you might want to know for which failure probability your S-N curve is defined. The customer wants us to guarantee a certain fatigue life using this norm, ASME VIII Div2. I'm trying to locate a norm or similar documentation, that we can use instead and that is better suited for regular machine components, where the failure probability is well defined.

Having this info, I might be able to issue a guaratee of a life of X years at load level Y, 2X years at load level 0.8Y etc. We can adjust the load level by using a different hydraulic relief valve pressure setpoint. Then I can leave it to the customer to choose combination of load level and fatigue life. It's a large 50 tonne forging, so we can't do destructive testing to get the actual S-N curve.

RE: ASME viii div 2 fatigue failure probability?

The smooth bar S-N curve has a nominal factor of 20 on mean life, but is generally accepted to just be a lower-bound on the minimum of the test data.

Personally, I would shy away from any guarantee on life for any fatigue analysis. But I play in the pressure vessel field, where other factors such as corrosion and corrosion-fatigue come into play.

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! Already a Member? Login


Resources

White Paper - Strategies to Secure Connected Cars with Firewalls
White-hat hackers have demonstrated gaining remote access to dashboard functions and transmissions of connected vehicles. That makes a firewall a vital component of a multilayered approach to vehicle security as well as overall vehicle safety and reliability. Learn strategies to secure with firewalls. Download Now
White Paper - Model Based Engineering for Wire Harness Manufacturing
As complexity rises, current harness manufacturing methods are struggling to keep pace due to manual data exchanges and the inability to capture tribal knowledge. A model-based wire harness manufacturing engineering flow automates data exchange and captures tribal knowledge through design rules to help harness manufacturers improve harness quality and boost efficiency. Download Now
White Paper - What is Generative Design and Why Do You Need It?
Engineers are being asked to produce more sophisticated designs under a perfect storm of complexity, cost, and change management pressures. Generative design empowers automotive design teams to navigate this storm by employing automation, data re-use and synchronization, and framing design in the context of a full vehicle platform. Download Now
eBook - Simulation-Driven Design with SOLIDWORKS
Simulation-driven design can reduce the time and cost of product development. In this engineering.com eBook, we’ll explore how SOLIDWORKS users can access simulation-driven design through the SOLIDWORKS Simulation suite of analysis tools. Download Now

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