stress-strain plastic material curve

[051174]

someone may help me on algoritm to define to build stress-strain curve for non linear material analysis?

 

[prost]

Given that there are an infinite number of nonlinear material constitutive relations, you'll have to be more specific. Are you talking polymer, metal, composite, bone, what kind of material?

 

[rb1957]

see also Ramberg-Osgood

 

[051174]

i'm talking of metal and in particular aluminium alloy

 

[rb1957]

that's good .. there is a lot of data available ... google (or yahoo, depending on your preference) "Ramberg Osgood elastoplastic"

 

[prost]

Depending on the aluminum alloy, there are Ramberg Osgood constants in MIL-HDBK-5; for instance, see Figure 3.2.3.1.6(a) for 2024-T3

 

[prost]

Anybody who needs the original Ramberg Osgood paper, NACA TN-902, go to

http://www.apesolutions.com/frm_link.htm,

near the bottom of the page you can download the PDF.

 

[rb1957]

or here

http://naca.larc.nasa.gov/,

click the "additional reports" button for a list of reports ...

 

[sdm919]

Are you trying to write an algorithm or use an FEA package?

Most FEA packages allow you to input an arbitrary stress-strain curve as a tabular set of data points, so you don't need an "equation" to do a plastic analysis using FEA software.

If you really need an equation, as already mentioned, Ramberg-Osgood is the most commonly used model in the Aerospace industry.

If you're writing an algorithm, you really should understand plasticity theory. The main points are the yield criterion, the hardening law, and the flow rule. It's not just a closed form stress-strain equation.

Here are some references:

Plasticity: Theory and Application by Mendelson
Fundamentals of the Theory of Plasticity by Kachanov
Continuum Theory of Plasticity by Khan & Huang