×
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

low creep aluminum

low creep aluminum

low creep aluminum

(OP)
We are constructing high precision parallel spring flexure structures by EDM machining of aluminum parts and we have problems with creep effects of the final structures. Could anyboby tell me which aluminum alloy should we employ for lowest creep? Where may I find such data?

RE: low creep aluminum

It's a little out dated, but the book "dimensional Instability" by Marschall from 1977 is a good primer.

2024-T6 is often employed for low capacity sensors.

There's couple charts for microyield behavior of of this alloy I could provide if you interested.

What kind of alloys have you tried so far?

Also if you find any other good references, please let me know.

Thanks,
Mark

RE: low creep aluminum

sensoptic,

Are you certain that creep is the problem?  Springs often have problems with high stresses near the limits of the intended travel, which can result in yielding.  Creep is associated with elevated temperatures, so what is the temperature range of this design?  Is the flexure essentially a cantilever beam with fully reversed loading?  Reiterating Mark's previous question, what alloys have you used so far?

RE: low creep aluminum

There was a review paper recently published in the Journal 'Materials Science and Technology' on creep in aluminum alloys.  It may be of some use ...
Citation:
Creep resistant aluminium alloys and their applications
Robinson J.S.; Cudd R.L.; Evans J.T.
Materials Science and Technology, 1 February 2003, vol. 19, no. 2, pp. 143-155(13), Institute of Materials.

Regards
David.

RE: low creep aluminum

(OP)
Thank you for the suggestions. We are using AA7075 at room temperature for our flexure structures. As suggested by Mark, AA2024 could be a better choice for precision applications. Our structure (10x10x1 cm3)is a linear translation stage operating as a pendulum for an inclination sensor application (like a swing moving laterally, only 2 deg), the two hanging arms have each two blade flexures. In fact, we are not sure that the creep (about 2% in one week) observed is due to the material or due to the structure design!

RE: low creep aluminum

1.  At room temperature, alloy 7075-T6 is essentially immune to creep.  Sources for creep data include the following:

MIL-HDBK-5H
http://www.grantadesign.com/MILpdfs/MIL5-H/MIL5H-3-7-4.pdf

Atlas of Creep and Stress-Rupture Curves
http://www.asminternational.org/Template.cfm?Section=BrowsebyTopic&template=Ecommerce/ProductDisplay.cfm&ProductID=10554

2.  It doesn't sound as if your application involves creep-- time-dependent strain based on the application of a static force.  I would recommend investigating the structure design & geometry, as there may be a problem with fixity/constraint, stresses, etc.

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