Do you want to plot stress-strain graph in ABAQUS, here is how?
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Three approaches for plotting stress-strain graphs in ABAQUS
I teach a finite element course in my university and with my students we do models involving ABAQUS. One of the common questions I always hear from my student is "How do I generate stress strain plot graphs in ABAQUS?" It is not such a strange question as there is no button within ABAQUS that can plot these graphs automatically. As a result, I had to make a video for my students showing them how to do so. I have re-mastered that video into a form that is suitable for you, my CM Videos Insider community and the YouTube audience. Here is the video, in case you have not seen it.
The thesis of that video is that if one wants to generate stress-strain profiles from ABAQUS, there are three possible strategies that we can use in doing so. These are what I described as:
- Localized stress-strain approach
- Volume-averaged stress-strain approach
- Experimental equivalence stress-strain approach.
(1) Localized stress-strain approach
This is essentially about probing local points within the test specimen to assess their stress and strain plots. It will require the user to isolate an element in the model, and probe its Field Output variables. For the instance considered in this video, which involved a tensile testing, the field output variables plotted were E11 and S11 which correspond to the strain and stress in the 1- or X-axis of the model. Whilst this method is viable and quick in generating stress-strain plot, it suffers from a localization effect. If you choose a different element, you might get a different plot and so it should be used carefully. It is not a recommended option for getting a global stress-strain profile for the structure. It is more of a nano-indentation type approach.
(2) Volume-averaged stress-strain approach
This second approach is a better way than the previous method because it removes the localization effect on stress-strain profile seen in the previous approach. Here, the user has to identify a region within the test specimen that one wants to average-out the behaviour of variables tracked in the model. It requires some prior work as you would have to identify the region, often the gauge section, and then track the History Output for such region. Like the previous method, you will have to track the S11 and E11 variables (at an integration point) for all the elements that belong to that region. In the end, using the avg(X,X,...) operation command in ABAQUS, you can generate the average values of stress and strain and that is your plot.
(3) Experimental equivalence stress-strain approach
This third method is not always intuitive as it requires a bit of lateral thinking. What it refers to is essentially creating a stress-strain plot that mirrors equivalently what you would do when physically setting up an experiment. The idea here is to extract the force and displacement profiles, as you would naturally extract from an experiment, and then operate on those based on the gauge length and cross-sectional area, A of the material to determine the normal stress and strain variables. To do so, the user will have to isolate a reference point where you will track the reaction force, RF1 and displacement, U1 variables in the 1- or x-axis. These variables are then post-processed to generate stress-strain profiles. It is the best method when you have experimental data that you want to compare with numerical predictions. It inherits the nuances/oddities of physical experiments as I discussed in more depth in the video above.
The Take-home messages
Having reviewed the three methods, the take home messages are as follows:
- It is possible to generate stress-strain plots in ABAQUS but it is not straight forward.
- Localized stress-strain plots is particularly sensitive to local regions being tracked and so not generalizable.
- Volume-average stress-strain plot, associated over a region, is the best way to generate stress-strain plots
- Experimental-equivalence stress-strain plots is best suited when comparing experimental data with numerical plots.
- Pre-planning is essential for generating stress-strain plots as you will have to identify the region and using the History Outputs option, you can track variables of interest during the simulation.
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