convergence issue with Drucker-Prager cap plasticity integration algorithm. How to sort this?

screenshot of my solver output.


MY APDL COMMANDS


/PREP7

et,matid,CPT215 !define matid to CPT215

KEYOPT,matid,18,2

MP,EX,matid,20000 ! Define Elasticity Modulus (enter a value for E)

MP,NUXY,matid,0.2 ! Define Poisson's ratio

TB,MPLA,matid,,,DPC !Define Drucker-Prager

TBDATA,1,31.6,36.34,3,1,40000,-35 !fuc,fbc,fut,Rt,D,sigVc

TBDATA,7,2,0,2e-5,3000,2000 !R,gamt0,gamc0,betat,betac

TB,MPLA,matid,,,NLOCAL

TBDATA,1,1600,2.5 !nonlocal interaction range c, over nonlocal parameter m

! Replace SOLID185 with CPT215

allsel

esel,s,ename,,SOLID185

emodif,all,type,matid

allsel

! Print out the result:

etlist,all

/SOLU

OUTRES,ALL,ALL

Answers

  • jjdoylejjdoyle PittsburghPosts: 135Member

    Your material model setup looks generally correct for a coupled damage-plasticity Microplane model. The format looks same as the example offered in Section 4.8.2.2 of MAPDL Material Reference Manual, with some of the strength values modified.

    The warning message that you are showing in solver output is very general. It could mean that the code cannot establish where the stress state is on the yield surface. Have you bisected to the smallest time step size? This might be remedied by using more substeps, but I cannot tell from the output if you have reached the minimum time step size or what your autotime stepping specifications are.

    Also, what is the motivation for using the CPT215 element? Are you trying to define a pore pressure thermal simulation? Perhaps you need to change the strategy of the loading to make it more manageable to resolve.

  • tolukumartolukumar Posts: 7Member

    Hi @jjdoyle . Actually I am using a minimum substep of 60 and a maximum of 100. But, the error still persists. I don't know how to solve it

    By the way, I am using CPT215, because I want to use drager prager plasticity criterion for seismic analysis of my concrete beam-column joint.

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