×
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

Jobs

Fatigue Testing

Fatigue Testing

Fatigue Testing

(OP)
Hi I'm after some advice

If I have a component that must flex 50 times through its life (2 months), I have an automated test fixture that will flext the component and check for a failure, (true return position).

If I wanted to prove that the component woudl not fail in normal operation say to 1:10,000 at 95%, I belive I'd have to test 30,000 parts to 50 flex's.

Now I only have 10 parts available, although completly representative of the final part.

So can I test each of the 10 parts to 3,000 actuations, and deduce the same fact. i.e

Is it true or fair to say, To test to a failure rate 1:10,000 @ 95%, I could either :-
Test 30,000 components, once each Or
Test 10,000 components, 3 times each Or
Test 1,000 components, 30 times each Or
Test 100 components, 300 times each Or
Test 10 components, 3,000 times each Or
Test 1 component, 30,000 times each ?

Some help would be great.

Thanks

Arron

RE: Fatigue Testing

Clearly, the last case cannot possibly yield a plausible answer.  You could survive 50 car crashes, but you'd be unlikely to survive 30,000 car crashes.

Moreover, since there are a number of long-term and thermal-related issues with fatigue failures that going past 500 actuationson a single unit wouldn't make much sense.  Some materials tend to work-harden, so exercising beyond a certain point fundamentally changes the parameters of the material itself, thereby nullifying any potential conclusions.  Likewise, mechanical working of a material that can fatigue induces heat, which can accelerate or otherwise alter material behavior as well.


On the other hand, if all pieces can handle 3,000 actuations, then there isn't a problem beyond whether the pieces you have really encompass ALL possible process and material variations.

TTFN

Eng-Tips Policies FAQ731-376


RE: Fatigue Testing

What do you mean by "1:10,000 at 95%"? Are you saying you want a 95% confidence that less than 0.001% of the components will fail?

What is the material? If metal, what is the loading vs. yield strength?

ISZ

RE: Fatigue Testing

Sounds like you are looking for Mean Time To Failure (MTTF)....

RE: Fatigue Testing

Using the true installation loadings, run about ten samples until failure and then do a Weibull analysis and follow it up by applying a 95% confidence limit. From the 95% conf curve, read off the B5 (the point where 5% of the population has failed, with 95% confidence)

Use some Weibull software, it takes away the headaches.

Bill

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!


Resources