Druker Prager material to simulate triaxial test

[siddharthfcb]

I used the following to simulate triaxial test on a 8 node brick element. But the response that I get is purely elastic and no hardening is observed in the output even if I vary kinf and ko by any amount. Please help .. Thanks



wipe
model BasicBuilder -ndm 3 -ndf 3
#--create the nodes
node 1 1.0 0.0 0.0
node 2 1.0 1.0 0.0
node 3 0.0 1.0 0.0
node 4 0.0 0.0 0.0
node 5 1.0 0.0 1.0
node 6 1.0 1.0 1.0
node 7 0.0 1.0 1.0
node 8 0.0 0.0 1.0
#set triaxial test boundary conditions
fix 1 0 1 1
fix 2 0 0 1
fix 3 1 0 1
fix 4 1 1 1
fix 5 0 1 0
fix 6 0 0 0
fix 7 1 0 0
fix 8 1 1 0


#--define material parameters for the model
#---bulk modulus
set k 27777.78
#---shear modulus
set G 9259.26
#---yield stress
set sigY 5.0
#---failure surface and associativity
set rho 0.398
set rhoBar 1.5
#---isotropic hardening
set Kinf 2
set Ko 21.0
set delta1 3.0
#---kinematic hardening
set H 0.0
set theta 1.0
#---tension softening
set delta2 0.0
#---mass density
set mDen 1.7

#--material models
# type tag k G sigY rho rhoBar Kinf Ko delta1 delta2 H theta density
nDMaterial DruckerPrager 2 $k $G $sigY $rho $rhoBar $Kinf $Ko $delta1 $delta2 $H $theta $mDen


#element
element stdBrick 1 1 2 3 4 5 6 7 8 2 0.0 0.0 0.0
puts "model Built.."

set p 0.5
set q 0.5
set pNode [expr -$p/4]
set qNode [expr -$q/4]
#--loading object for hydrostatic pressure

set Time 0.0
wipeAnalysis
pattern Plain 1 Constant {
load 1 $pNode 0.0 0.0
load 2 $pNode $pNode 0.0
load 3 0.0 $pNode 0.0
load 5 $pNode 0.0 $pNode
load 6 $pNode $pNode $pNode
load 7 0.0 $pNode $pNode
load 8 0.0 0.0 $pNode
}

integrator LoadControl 0.1
numberer RCM
system SparseGeneral
constraints Transformation
test NormDispIncr 1e-5 10 1
algorithm Newton
analysis Static
analyze 10


#--loading object deviator stress
pattern Plain 2 Linear {
load 5 0.0 0.0 $qNode
load 6 0.0 0.0 $qNode
load 7 0.0 0.0 $qNode
load 8 0.0 0.0 $qNode
}

#-------------------------------------------------------
# create the analysis
#-------------------------------------------------------
#record nodal displacements

recorder Node -file displacementsDPiso.txt -time -nodeRange 1 8 -dof 1 2 3 disp
# record element displacements
recorder Element -ele 1 -time -file stress1DPiso.txt -dT 0.001 material 2 stress
recorder Element -ele 1 -time -file strain1DPiso.txt -dT 0.001 material 2 strain
recorder Element -ele 1 -time -file stateDPiso.txt -dT 0.001 material 2 state
recorder Element -ele 1 -time -file LoadDPiso.txt -dT 0.001 material 2 globalForce
record

puts "recorders set"

integrator LoadControl 0.01
numberer RCM
system SparseGeneral
constraints Transformation
test NormDispIncr 1e-5 10 1
algorithm Newton
analysis Static
analyze 105000

puts "triaxial shear application finished..."

[skamalzare]

You might need to update your material stage to plastic and then perform another analysis. By default materials are set to elastic behavior. After your first gravity analysis, you might need to add:

updateMaterialStage -material $mattag -stage 1

[siddharthfcb]

Thank you for your suggestion.. I tried it , but it still doesnt work!! The manual says that the updateMaterial command is for PressureDependMultiYield . Should it also work for Druker Prager material?? Thanks