Help with Drucker-Prager parameters

[mcl1463]

Hello,

I am trying to model nanoscratching of High Density Polyethylene, and I am going to compare the results obtained by 3 different models (Viscoelastic, Drucker-Prager and Mohr Coulomb).

I am having difficulty obtaining the angle of friction, dilation angle and flow potential eccentricity for the Linear Drucker-Prager model. What is the p–t stress plane? Also, the major problem I have is that I do not have any triaxial test data for this material, therefore, I was thinking of using a suboption to compensate for this.

I know that the Mohr-Coulomb parameters can be matched with Drucker-Prager, but I do not have those parameters yet.

Thanks in advanced :).

[FEguru]

The p-t plane is similar to the p-q plane (pressure vs. Mises stress), with the exception that it accounts for the K factor that makes the yield/flow surface in the deviatoric plane non-circular.

Good calibration of the Drucker-Prager material model requires experimental data obviously (to determine friction angle, dilation angle, K, and hardening if necessary). Personally, I view the flow potential eccentricity as a numerical parameter to facilitate convergence. If you don't have enough experimental data to evaluate K you can assume it to be K=1.0 (which gives the original Drucker-Prager material), or if you have the Mohr-Coulomb parameters you can find an appropriate matching K value (according to the Abaqus documentation for matching these two material models).

By the way, I would not recommend using either the Mohr-Coulomb or the Drucker-Prager material models for High Density Polyethylene. Why not use a viscoelastic material?

[mcl1463]

We are beginning to model viscoelastic, but we are stuck on choosing what parameter to use to model plastic deformation as well.

What do u recommend for this?