During the last years a good time and effort has been spent to obtain a more reliable way to calibrate elastomeric materials.This post makes available to the community a new Hyper+Prony calibration method using Isight, a C++ calibration tool and a real-time curve-fitting visualization GUI. 

Relative to the past work, this is a continuation of LI ZHANG's work available in the community, Calibration for Hyper-Viscoelastic Material using Isight + Fortran. The suggested mathematical model for calibration is now completed and fully integrated in the new C++ tool, allowing the user to perform a more accurate calibration using three different types of test data: Uniaxial, Equibiaxial and Planar.

Calibration tool

The new calibration tool was migrated from Fortran to C++. It allows the use of different Hyperelastic models like Neo-Hooke, Yeoh, Ogden (order N=1 to N=6), Arruda-Boyce, Van Der Waals and Mooney-Rivlin. However, until this date, only the integrated calibration with Neo-Hookean, Yeoh and Ogden are validated. 

The image above is an overview of the calibration tool workflow with all necessary input files and generated output files. The attached documentation gives a more in-depth explanation how the program works, the format requirements for the different files, the used error norm and some general considerations about the use of the program.

The calibration is performed using 5 different sets of  Butyl Rubber test data. During the experiments, it was noticed that better calibration results can be achieved when the different data sets have approximately the same amount of data points. The new decimated version of the data sets can be found inside the attached .zip file.

Isight Model

One of the big issues on the material calibration subject is the diversity of possible answers. That makes the process more difficult in the sense of defining which one is the best. With that in mind different Isight models were tested, with the goal of getting a configuration able to produce good results consistently. The suggested Isight model is based on the previous models with some differences: it uses Pointer-2 as the optimization algorithm and a  calculator component to constrain the g prony terms values. All the detailed information about this model is present on the attached documentation.

Graphics GUI

This Graphic GUI was developed to solve one of the past stated drawbacks. It's a standalone application with the purpose of seeing the curve fitting results not only at the end of the process, but while the optimization process runs. The application needs all the input & output files generated by the C++. It allows the display of 12 different plots.

Attachments Explanation

The attached .zip file contains 5 different folders inside:

• "Butyl_Data_Decimated": decimated test data used on the calibration
• "Input Files": Different types of input files formatted for the supported Hyperelastic models
• "Documentation": Two different files: "Calibration for Hyper-Prony_equations" has the derivations of the equations of the mathematical model and "Calibration for Hyper-Prony_Cplus_Isight" has a detailed explanation about the calibration process and its components.
• "Run_Dir": Folder "ready-to-run" that includes already all the necessary files.
• "Source Code": C++ tool and GUI source codes

Video tutorials:

(Download the videos for better image quality)

Building the Isight model from scratch (download):

Run the calibration process from the predefined folder "Run_Dir"(download):

Back to: Simultaneous and Integrated Calibration of Hyperelastic-Viscoelastic Materials

Back to: Material Modeling and Calibration - An Overview and Curriculum