A common starting point when examining material model calibration issues is to focus on elastomers and the hyperelastic material model. This is a nice starting point because we have known equations for the stress-strain relationships in hyperelastic models. The stress-strain equations for all of our hyperelastic models are given in the Abaqus documentation. When you have known equations, then you can examine the calibration issues in a manual derivation way, or use fairly simple Excel spreadsheets to examine material model behavior, and the Excel solver to solve for the model coefficients (aka parameters). The beauty of this is that the underlying calibration issues and concepts are well exposed. This tutorial, and it's narrated videos are best viewed after reading this file:
W01-Q-ManualFit.pdf (Workshop pdf document)
This file is available for download alone or also contained in the zip file. The zip file contains two pdf's and a python script used in the workshop.
Please take a moment to download and read through this workshop document. Once you have read through it, you will notice that we are limiting our scope in this tutorial to: a) the simplest form of hyperelastic material model called neo-Hookean, b) only the uniaxial deformation of an elastomer. The two files have been used in the past as the first workshop in our course "Testing and Analysis of Elastomers". After reading the first downloaded document, then listen to this narrated PowerPoint Presentation (download video here):
After reading the Workshop document (pdf file) and then listening to the above narrated PowerPoint video, we will now take a look at an Excel spreadsheet used to explore various concepts and issues that arise when calibrating a material model. The Excel spreadsheet is named Neo_Hooke_curve_fit as is available for download. Please listen to this video (or download video here):
And now, for completeness, I have also added a video that shows how we could obtain the same neo-Hookean coefficient using the hyperelastic calibration tool in our Abaqus/CAE software (you can download the video here):
I'd be very interested to know if you have a favorite publication, or website, that does a good job explaining error measures (error norms) for purposes of curve-fitting or calibration ?
If this tutorial was helpful for your work, you might like to continue on this hyperelastic model calibration subject with:
"Yeoh Model Calibration of an Elastomer"
The attached documents are:
uniaxial_data.txt This is just the uniaxial test data for use with Abaqus/CAE curve-fitting. Stress in column 1, strain in column 2.
Neo_Hooke_curve_fit.xlsx This is the Excel spreadsheet shown in the 2nd video.
W01-Q-ManualFit.pdf Workshop 1 pdf document, please read this before viewing the entire post.
Workshop_Manual_Fit.zip This zip file contains: W01-Q-ManualFit.pdf, W01-S-ManualFit.pdf, and ws_manual_fit.py
Neo_Hooke_curve_fit_ST_S58.xlsx Bonus spreadsheet - same format as the other sheet, but different and more test data
Back to: Material Modeling and Calibration - An Overview and Curriculum
