Image courtesy of Axel Products test lab

Originally posted in August of 2023.

The image above shows the use of a clip-on extensometer to measure the displacement in the center region of a uniaxial dogbone specimen.  There are a variety of reasons why one might want to model the entire dogbone specimen and use the extensometer test data as part of an FE mode calibration.  This post shows a worked example of how to do this.

In Abaqus the extensometer (or alternate imaging techniques) can be mimicked by using an axial connector element.  In the 3DExperience material model calibration app, this is enabled in FE mode by allowing the displacement simulation data to come from a connector element (single element elset) and compare this to the extensometer test data.

For my example, the specimen is pulled at the grips with a constant velocity.  But the measured displacement at the extensometer is not linear over time because of plasticity occurring in the gauge section of the specimen.  For this calibration workflow, one needs to know both the grip motion information (displacement / velocity) and the measurement from the extensometer. Hopefully the test lab has recorded both of these pieces of information along with the time and the load cell force. 

In the image below we show the force-time and the CU1-time.  The test data is synthetic.  The test data was imported as a single dataset. Outside of the calibration app the dogbone model runs in ~38 secs.  Units are N, mm, MPa.

The material model used to generate the synthetic test data was:

*Material, name=Teflon
*Elastic
550.0, 0.4
*Plastic, hardening=Johnson Cook
3.5163, 44.0130, 0.65304, 0, 2000, 1000

This work was performed in R2023x HF3.11 on Aug 1, 2023.

The image below shows the initial set-up of the calibration.  I have perturbed the material model by changing the Johnson-Cook A and B parameters.  In this image we show a Force-Time plot and a Displacement-Time plot.   

If we desire we could also plot the Force-Displacement :
 

This narrated video starts from scratch and steps through a worked example of using extensometer test data.

The attached zip file contains:

• 3dxml file of a simple dogbone with axial connector element extensometer.
• The Abaqus run-ready FE model. (dogbone.inp)
• The synthetic test data. (fake_test_data.txt)

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