# Dyna result doesn't match Test result

1. Jul 21, 2010

### lambertlai

I try many time to model a simple tensile test for steel MAT_024 but the graph doesn't match from Dyna result and Test result.
Process:
1. Collect data Tensile strain and stress convert to True stress and strain use formula True stress: eng. stress*(1+eng. strain). True strain= ln(1+eng. strain) and then the true strain convert to plastic strain = true strain - (true stress / Young modulus) and plot the graph

2. Use MAT_024 from dyna

3. Then I extract nodout and sec force.

LN1 is left node 1 (triangle on left)
RN1 is right node (triangle on right)

4. Eng stress= Force/Ao and eng. strain= delta Length / original length and plot the graph. (original area is 40, original length is 45mm)

Then the both result was different, why? What the misstake? Anyone can help me solve this problem?

Last edited: Jul 21, 2010
2. Jul 22, 2010

### john.phillip

In the first figure, when you define the stress x plastic strain for the material, the maximum inputed value is around 0.5GPa for a strain of 0.3, but when you show the lab test stress x strain graph in the last figure, the maximum stress is around 0.37GPa for the same strain.

3. Jul 23, 2010

### lambertlai

The 1st figure is a plastic strain vs true stress as a input, is it right?
if true stress vs strain and lab test strain stress the max. stress is different right?