ABAQUS - Steel Rod Tension Test

[MTohmeh]

Hello,

I am a very new user to ABAQUS and I am attempting to do a simple tension test on a steel rod to see if I can match up my theoretical stress-strain curve to the one being output by ABAQUS.

My steel rod properties are as follows:

Density:
Density = 0.000730 lb-s²/in²

Elastic:
Young's Modulus = 28661481.06 psi
Poisson's Ratio = 0.3

Plastic:
Yield Stress (psi) / Plastic Strain (in/in)
60126 / 0
60445.0074 / 0.005263826
69475.5558 / 0.017378623
81969.7216 / 0.036360787
91223.0488 / 0.055086133
94979.59041 / 0.066305501

But when I run the analysis, I go to XY Data and combine the PE22 with the S22 and get a Stress-Strain curve that almost matches perfectly with the theoretical Stress-Strain curve, except for the first two data points, which gives me a slope (E = 5458162.467) instead of the theoretical slope (E = 28661481.06)

ABAQUS:
Strain / Stress
0 / 0
0.0116319 / 63488.8
0.0287301 / 74957.4
0.0440649 / 83862.3
0.064943 / 92761.9
0.0661112 / 92633.6
0.065971 / 88998.3
0.0658559 / 86000.1
0.0657489 / 83182.5
0.0655604 / 78208.7
0.0654334 / 74880.6
0.0653874 / 73679.1
0.0653204 / 71926.1
0.0652243 / 69412.4
0.0650904 / 65905.9
0.0649115 / 61220.5
0.0648263 / 58990.7

Any help would be appreciated as I am very new to ABAQUS and not very experienced with FEA programs.

Thank you

 

[MTohmeh]

To clarify my problem,

I am applying a displacement to determine the elastic and plastic behavior of the rod through the stress-strain curve, but I get different values for the slope in the elastic region. Changing the displacement also has a large effect on the linear (elastic) portion of the stress-strain curve.

 

[burningDiesel]

At your first increment:
0.0116319 / 63488.8
you are already well into the plastic region. Start with getting more output in the linear region

 

[MTohmeh]

Thank you very much for your reply, as I have been stuck on this problem for days.

Forgive me if this question may sound stupid, but how would I go about getting more output in the linear region?

Thank you again for your reply

 

[burningDiesel]

just increase the output frequency and ask for exact output times, or decrease the initial and maximum step size at the step dialog

 

[MTohmeh]

Hello again,

These are now the new results I am getting when increasing the output frequency:

ABAQUS:
Strain / Stress
0 / 0
0.000744291 / 60460.3
0.00224891 / 61136.1
0.00450245 / 62148.3
0.00784938 / 63988.1
0.0128502 / 66867.8
0.0203003 / 71398.5
0.0313252 / 78655.2
0.0477414 / 87593.5
0.0537317 / 90553.8
0.0559898 / 91525.6
0.0587716 / 92457.1
0.0601022 / 92902.7
0.0608245 / 92562.4
0.0608245 / 91037.2
0.0608245 / 90303.4
0.0608245 / 88864.7
0.0608245 / 88108.2
0.0608245 / 86992.7
0.0608245 / 85386.4
0.0608245 / 82994
0.0608245 / 79539.4
0.0608245 / 74673.1
0.0608245 / 68097.8
0.0608245 / 66588.2
0.0608245 / 65132.2
0.0608245 / 63047.4
0.0608245 / 60134.5
0.0608245 / 56187.4
0.0608245 / 54809.9
0.0608245 / 52805.6
0.0608245 / 52315.2
0.0608245 / 51104
0.0608245 / 50037.8
0.0608245 / 48488.8
0.0608245 / 46287
0.0608245 / 43259.5
0.0608245 / 40936.8

Which gives me a slope of (E = 81,232,071.86), I just can't seem to figure out why this is having such a big impact on my stress-strain curve, I'm thinking there must be some sort of problem that I'm just not seeing.