×
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

FEA Non-Linear Analysis

FEA Non-Linear Analysis

FEA Non-Linear Analysis

(OP)
When "he" say: o man this is non-linear, he means result in his hand is last word, so no comment on accuracy should be made. This is in top level (or is suppose to be) engineering in Detroit automotive.
I can see more and more often that FEA word becomes excuse for non-ability to understand mechanical engineering at all. FEA C-A-N be made to be useful SOMETIMES.
Properly used, in calculation of stresses, among 100 lines of calculation, FEA result as input into calculation takes only 2 lines (Form Factor and Nominal Stress).

Now about that NON-LINEAR
When "FEA" calculates it does not calculates deformations and stress separately as two independent calculations. "FEA" calculates only ELONGATION, and stresses are post-calculation from elongation (it is why stresses are less accurate then deformation, one error more is made).

When elongation due to loads and constraints is calculated at the point, stress is: (total elongation) x (E modulus of elasticity)
example: elongation = 0.0002, E=210000, stress=0.0002*210000=42 N/mm^2 (try this on your computer)
This is calculation along straight line and it is why it is called linear.
When "yield" is past, real stress swings away from the straight line, and if we continue to use linear analysis error is made.
Now comes non-linear as need.
Is FEA useful at all in non-linear? If one is not close to expert in metal forming unknown error is on the way.
The best way “non-linear” is to do linear analysis and find elongation. Make FLOW curve for the material (by hand on a paper). Draw vetrical line with known elongation, up to curve, then draw to left ordinate showing stress. You got real stress.

It is that simple and accurate as your FLOW curve is. Flow curve is (Stress)-(Logarithmic elongation) curve. Engineers working in field as bending, drawing, forging, .. (all above yield, so "non-liner" guys) knows it.
No non-linear analysis, in so many cases, is not even and close to real stress. E.G. Hertzian stress, Press Fit, .. and yields very large errors done by computer.
FEA C-A-N be very useful only in hand of "good engineers" not computer cables.

So lets comment on non-linear FEA (actually FEM).
With High Respect

RE: FEA Non-Linear Analysis

in theory it is simple to predict stress. simply obtain deformed shape, have enough gauss points in the correct area to capture stress distributions and use a suitable material model and hey presto.

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