This post contains some synthetic test data - created from a reasonable Drucker-Prager material model for a thermoplastic. It is well known that many thermoplastics have a pressure-dependent yield. The Drucker-Prager material model has a pressure-dependent yield surface and can be calibrated using a variety of test data - perhaps the simplest is testing in uniaxial tension and uniaxial compression.
This conversation is limited to linear DP (LDP). Also limited in scope to the example of polymers/plastics. The LDP model has a conical shape of the yield surface and the parameter beta, friction angle, controls the cone angle.
If beta=0, this becomes the Mises cylinder. The bigger beta gets, the bigger the difference between the compressive yield and tensile yield.
For polymers it is common to test in uniaxial tension and uniaxial compression.
It is also common to set the stress ratio, K=1, meaning the shape is circular in the deviatoric plane (PI plane).
It is also common to set the Dilation angle to 0.0 (no change in material volume while yielding).
So, within this polymer context, the typical calibration amounts to defining:
- E and nu (pretty easy)
- The hardening curve. (pretty easy)
- Beta
The hardening curve should be created directly from either (any) of the test datasets. (uni tension, uni compression, shear)
In many cases the core issue becomes the determination of beta.
The video below uses the attached test data and calibrates a rate-independent Drucker-Prager material model. This video was created using a beta version of what will be 2020x FD04.
The Excel file attached to this post contains synthetic test data for uniaxial tension and uniaxial compression at a slow rate (rate=0.01). Plus there are additional data sets for uniaxial tension at a rate = 1 and rate=10. These additional data sets can be used to calibrate a Drucker-Prager rate-sensitive material model.
The Excel file also contains the Abaqus model file that was used to produce each set of data.
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Back to: Calibration examples, including narrated videos
Back to: Material Modeling and Calibration - An Overview and Curriculum
