×
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

Bending Moment Induced by Shims

Bending Moment Induced by Shims

Bending Moment Induced by Shims

(OP)
This is a rather embarrassing riddle for me since I've been in the aerospace industry for 20 yrs now:

We have a skin 0.130 thick that has a dent at the edge. The dent is 0.040 out of plane over about 5.0 inches wide.
Residual stresses are about 15 KSI. We are not going to reverse bend it (not allowed of course). We will be able to lay it up and shim out the gaps. Even with the residual stress I can show it good statically and for crack growth.

PROBLEM: I made the mistake of reviewing the Mc/I bending stress induced by the 0.040 thick shim. When you add this bending stress to the residual stress I can NOT show this part good.

EXAMPLE: Take a strip model 1.0 wide X 0.130 thick with 10 KSI axial tension stress. Make it eccentric by 0.040 inch. This creates a bending moment of 18.5 KSI which is significant.

I know intuitively that it is overly conservative to add the entire bending moment induced by an 0.040 shim due to the fixity of the adjacent structure. I know that the load will really want to go straight and the load will redistribute around this hump. Heck, we shim stuff in this range all the time.

QUESTION: How do I prove that this 18.5 KSI is not real and/or not a concern? (Without a horrendous spring model or FEM project)?

RE: Bending Moment Induced by Shims

EasyAim,

It could be that you are using the wrong theory to analyize your situation.

According to Seely & Smith (Advanced Mechanics of Materials, 2nd Ed.), plates may be divided into three groups. "Thick plates", in which shearing stresses are important, "medium-thick" plates in which bending is the main means of resistance, and "thin plates" who useful resistance depends in part on direct tension.

I suggest you do some research into thin plate theory and see if your situation improves.

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