Drucker Prager Plasticity model

Hi All,

I am trying to code the Drucker prager plasticity model for the 2D plane strain case using consistent tangent modulus. I am using C++, therefore I would appreciate if anyone could share relevant materials which I could use and preferrably for the 2D case so it is not unnecessarily complicated.

I have already seen some codes written for the 3D case,however I am not sure if I am converting it to the 2D case right, as it does not work at the moment. For the consistent tangent modulus, I have to return a 3*3 matrix to the program for 2D with the coefficients for the x,y and xy directions. What I am doing currently is just selecting relevant members from the general 3D tangent matrix(6*6) and ignoring the z direction. Is that wrong?

Thank you!

Setareh