Power of SIMULIA Portfolio 8:
Simultaneous and Integrated Calibration of Hyperelastic-Viscoelastic Materials
Integrated Hyper+Prony Calibration solution
There is a capability in Abaqus/CAE to calibrate a hyperelastic material model and to calibrate a linear viscoelastic, Prony series, model. But these calibrations are separate and independent. In our classes on rubber: "Modeling Rubber and Viscoelasticity with Abaqus" and "Testing and Analysis of Elastomers" , we teach you how to use the calibration tools in A/CAE, but the key element is that the hyperelastic calibration uses one kind of test data and the Prony series calibration uses a different kind of test data. The test data used in the A/CAE Prony series calibration is often taken from a portion of the stress relaxation test. This means
- the user has to chop apart and modify the actual test data prior to its use in Prony series calibration.
- the viscoelastic calibration process assumes one can determine either the "instantaneous", or "long term" hyperelastic material model.
The tools in A/CAE have been used successfully for two decades by people in sealing/gasket applications. This is because their typical time frame of interest for the viscoelastic behavior is quite long (hours, days, weeks) compared to the time frame of the hyperelastic test (seconds, minutes). For that class of problems the fact that the A/CAE calibration process "bakes" some viscoelastic behavior into the hyperelastic definition of the material model was acceptable.
About a decade ago, we started to struggle with helping people interested in other applications, especially where the time frame of interest was much shorter. At short time frames in drop testing and crash applications, there were no tools available to us for calibrating a Hyper+Prony material model in a simultaneous and integrated fashion from test data such as a family of rate curves (shown in the image above, and posted in Butyl Rubber Test Data). Our struggles led us to try to accomplish testing that would fit into our available calibration tools, see the post: Hyper-visco rubber material models in Abaqus. As the Isight optimization software became part of the SIMULIA portfolio, another solution approach was to run reverse engineering optimizations using an Abaqus unit-cube single element model with the hyperelastic+Prony series material model. The downside to this approach is that it can be quite slow owing to the hundreds and hundreds of simulation runs involved.
A better solution is to create newer calibration tools around a set of math that integrates the Hyper+Prony response and can be applied to any time-varying test data. In recent years, the calibration tool, MCalibration by Veryst LLC, has done just that. For the past several years a few of us at SIMULIA have also gradually developed internal tools based on a set of math equations for the integrated Hyper+Prony response. This post, by Li Zhang :
Calibration for Hyper-viscoelastic Material
makes some of those ideas and tools available to you. The solution process that Li describes in his post has a drawback that we are trying to address – there is no graphic depiction of the stress-strain curves evolving as the optimization process unfolds. Li produced a script to get the stress-strain plots at the end of the process. It would be better to see the stress-strain curves evolving as the optimization process proceeds. We are working to address that issue, and hopefully will have a new post soon to share that with you.
Here is the eSeminar recording, Power of SIMULIA Portfolio 8:
Simultaneous and Integrated Calibration of Hyperelastic-Viscoelastic Materials
(this narrated video can be downloaded for better viewing fidelity)
