Some years ago, even before Isight became part of the SIMULIA portfolio, I became interested in the idea of material model calibration using general purpose optimization methods. This interest led to an Abaqus Technology Brief back in 2007. For some material models, and for some simple deformations, calibration tools are available within Abaqus/CAE. But what happens when you are outside that scope? If the deformations are still simple, and you know the equations of those simple deformations, you can use Excel to calibrate material models - since Excel has a built-in optimizing solver. Using Excel is pretty interesting in its own right since it forces you to think about error measures, data comparison, etc. In other cases, especially when you don't know the equations behind the material model, or when the deformations are not simple, you could use a general purpose optimizer driving a series of Abaqus analyses to perform material calibration. For years, perhaps even decades, I'd run across customers who had a standard ASTM rubber puck, compressed with friction, or even bonded to the fixturing. A test person might call this "uniaxial" since it is only loaded in one direction, but from a solid mechanics perspective, this is not uniaxial compression. This is a highly complex deformation that excites both the shearing of the material and the material's bulk modulus. And since for rubber the bulk modulus is roughly 2000 times the shear modulus, this causes a big difference from the real "uniaxial compression" definition. This complex deformation is characterized by bulging of the vertical sides of the rubber puck as the deformation progresses as shown here.
There is no single equation that describes the stress-strain relationship for this complex deformation. But if we trust that Abaqus can accurately model this deformation, then we can use Isight to drive a series of Abaqus analyses to calibrate, or reverse engineer, the correct hyperelastic material model coefficients. I want this post to also serve as a learning tutorial, so am I providing all the needed files for you to learn from, and repeat this exercise on your own computer. First, watch this narrated PowerPoint video that describes the overall problem and solution.
Now that you understand the problem we want to solve, we will walk the set-up of the Isight model using another narrated video. This problem was solved using earlier versions of both isight and Abaqus, but since we are using fairly basic functionality, it can also be set up in more recent versions.
After watching the two videos, you should be able to follow the demo script (in zip file) and open a a new Isight session (double click on the null.zmf file) and build this Isight process capture. The attached zip file Bonded Rubber Puck.zip (at bottom of post) contains the following:
Demo - Script for Bonded Puck.docx - Guidance sheet to set up the Isight work-flow
null.zmf - Optional empty Isight model to build the work-flow
puck_bonded.inp - Abaqus analysis input file
puck_bonded.odb - Abaqus output database file
puck_bonded.sta - Informational Abaqus status file generated for the analysis
RF2_Test_Data.txt - Text file containing the test data used for Data Matching
puck_bonded.zmf - Complete Isight model
puck_bonded.zrf - Results file generated from the completed Isight model
Note that the model has been created using Isight 5.0 and Abaqus 6.10
To simply run the Isight work-flow:
1) Extract the contents of the zip file to a folder on your machine.
2) Start Isight 5.0 Design Gateway and open the puck_bonded.zmf file.
3) Execute the model.
Note that SOSS answers 4212 and 4765 explain the usage of the Abaqus *PARAMETER keyword with the Isight Abaqus Component.
Let me know if you have any questions or comments about these files.
