Problem in plotting graph in Abaqus

[Souhardya Roy]

I want to draw the graph between stress and strain of an Aluminum hybrid foam in Abaqus and validate it with a research paper. In the paper, the graph is between stress and strain however, I am not getting strain as any field or history output in my Abaqus simulation after the results. I am getting something called Logarithmic strain (LE). Is it because I am using foam? The graph is not coming as intended however, the values of max stress and strain are almost close to the actual values in the paper, the strain is logarithmic strain which is coming close to the actual normal strain in the paper. Also, I am getting a linear graph though, it should be like the one shown in the picture. Please guide me on this. I have attached the pictures of the output and the graphs.

 

[FEA way]

There are several different strain measures. You can find their description in the documentation chapter Abaqus Introduction & Spatial Modeling --> Conventions --> Stress and Strain Measures. Logarithmic strain is used for output in the case of hyperelastic materials. Are you still using crushable foam plasticity with linear elasticity ? Is the same material model used in the research paper ?

 

[Souhardya Roy]

Yes. But I am not getting the correct results. Can you tell me in what units should I put the density (=2g/cc) to get consistent results? The length is mentioned in mm, Young's Modulus and Yield Stress are plotted in Mpa and max load is 9816N. The strain rate is 0.1s^-1, so how shall I incorporate that in Abaqus? By fixed increment = 0.1? And the time for the test is 5s, does that mean that the time period should be 5 in the step module? Also the test is carried out in 500 steps, so shall I put the maximum increments as 500 in the step module?

 

[FEA way]

With this unit system, the density should be in tonne/mm^3. You can specify the parameters of automatic incrementation like this: step time period = 5 s, initial increment = 0.01 s, maximum increment = 0.01 s. The minimum increment can be much lower than that for potential convergence issues. Also, keep the maximum number of increments high too for the same reason. You can control the strain rate (rate of load application) using the amplitude definition.