Elastic Plastic Material Data

[roman.gebhard5MV47]

Hello,

i'm trying a nonlinear analysis (nonlinear material analysis).

I defined a low tangent modulus and i do not understand why my max. stresses still increasing so much?

It first hits the yield strength of 235MPa with a load factor of approx. 0,4.

The stresses are not increasing with the e-modulus (so the nonlinearity functions) but it's still increasing too much at this place?

in my Opinion it's only allowed to slowly increase (with the tangent modulus)...maybe lately with a loadfactor of 1.0 around 240MPa

But the stresses are going up to 301MPa with a load factor of 1.0.

Do you know a solution for this or better nonlinear properties to get the right results?

[John_Holtz · Accepted solution]

Hi @roman.gebhard5MV47 

Based on your input, and making the stress-strain graph,  it only takes 3.28% strain to reach 301.5 MPa stress. That does not seem too unreasonable. I think the result is accurate, especially since the "red" region of stress is a large area surrounding the maximum value. (If it required 30% or 300% strain to reach that stress level, then I would say it is unreasonable.)

In some models the maximum occurs at one corner of an element while the other corners on the element are either near the yield stress or below the yield. This occurs because the result shown in Inventor are extrapolated from interior "nodes" whose stress follows the stress-strain curve to the corner nodes. The extrapolation can exaggerate the maximum stress value when there is a large stress gradient. See this article for more details: Equivalent stress in a nonlinear analysis with Autodesk Nastran

John