STRESS-STRAIN PROBLEM IN LAYEREDSHELL

[dgale]

Hello everyone,
I'm using shell and beam elements in my model and I have found out that the elementsShellMITC4 with section LayeredShell doesn’t follow the constitutive equation, shows a higher strength than the maximum strength defined for the material.

I want to show the wrong behaviour of this kind of element with a little model. I would like you try to run it in order to verify if you arrive to the same conclusion, since I’m going crazy.

The aim is to model a plate supported in two of its edges and apply a boundary condition in the node of the middle of the span (node 28), which can be a displacement or a rotation. When we apply a total displacement of 25mm (dof=3; dU=-0.1e-3), we get the following stresses and strains:
Stress in the most compressed fiber (elem 23; gp 1; fiber 11) :

file: stress23111.txt
T Sigma11 Sigma22 Sigma12 Sigma 23 Sigma31
250 -1.4312e+007 -3.79452e+007 9.08435e+006 5.40476e+006 5.63637e+006

Where we can see that Sigma22>30e6 Pa. The latter is defined in the material features, which is shown below.
# Concrete fc ft fcu epsc0 epscu epstu stc
nDMaterial PlaneStressUserMaterial 3 40 7 30e6 4e6 -30e6 -0.0025 -0.0035 0.1 0.08;

In the case of the most tensile fiber the material behaviour is good (elem 23; gp 1; fiber 1)

On the other hand, when we apply a total rotation of -0.025rad (dof=4; dU=-0.1e-3), I get the following stresses and strains:

Stress in the most compressed fiber (elem 23; gp 1; fiber 11) :

file: stress23111.txt
T Sigma11 Sigma22 Sigma12 Sigma 23 Sigma31
250 2.64751e+007 -8.64711e+007 -5.65509e+007 2.67003e+006 1.83978e+007

Where we can see again that Sigma22>30e6 Pa and the material definition is the same.

In the case of the most tensile fiber the material behaviour now is wrong (elem 23; gp 1; fiber 1)

file: stress2311.txt
T Sigma11 Sigma22 Sigma12 Sigma 23 Sigma31
250 -2.16182e+006 9.86725e+006 8.1899e+006 2.67003e+006 1.83978e+007

Since as we can see Sigma22>4e6 Pa.

After having shown the results above, from my point of view the material behavior is wrong. But I hope I have committed an error.

I'm looking forward your replies.

CODE:
-----------------------------------------------------------------------Copy from here below--------
wipe;
model basic -ndm 3 -ndf 6;

# ------------Only change the following parameters ----------------------------

set dof 4; # dof where apply the displacement
set nsp 28; # node where apply the displacement
set dU -0.1e-3; # Displacement in each iteration

# -----------------------------------------------------------------------------
# MAIN CODE

# NODES
node 1 0.0 0 0
node 2 0.2 0 0
node 3 0.5 0 0
node 4 0.8 0 0
node 5 1.0 0 0

node 6 0.0 0.2 0
node 7 0.2 0.2 0
node 8 0.5 0.2 0
node 9 0.8 0.2 0
node 10 1.0 0.2 0

node 11 0.0 0.4 0
node 12 0.2 0.4 0
node 13 0.5 0.4 0
node 14 0.8 0.4 0
node 15 1.0 0.4 0

node 16 0.0 0.6 0
node 17 0.2 0.6 0
node 18 0.5 0.6 0
node 19 0.8 0.6 0
node 20 1.0 0.6 0

node 21 0.0 0.8 0
node 22 0.2 0.8 0
node 23 0.5 0.8 0
node 24 0.8 0.8 0
node 25 1.0 0.8 0

node 26 0.0 1.0 0
node 27 0.2 1.0 0
node 28 0.5 1.0 0
node 29 0.8 1.0 0
node 30 1.0 1.0 0

node 31 0.0 1.2 0
node 32 0.2 1.2 0
node 33 0.5 1.2 0
node 34 0.8 1.2 0
node 35 1.0 1.2 0

node 36 0.0 1.4 0
node 37 0.2 1.4 0
node 38 0.5 1.4 0
node 39 0.8 1.4 0
node 40 1.0 1.4 0

node 41 0.0 1.6 0
node 42 0.2 1.6 0
node 43 0.5 1.6 0
node 44 0.8 1.6 0
node 45 1.0 1.6 0

node 46 0.0 1.8 0
node 47 0.2 1.8 0
node 48 0.5 1.8 0
node 49 0.8 1.8 0
node 50 1.0 1.8 0

node 51 0.0 2.0 0
node 52 0.2 2.0 0
node 53 0.5 2.0 0
node 54 0.8 2.0 0
node 55 1.0 2.0 0

# BOUNDAY CONDITIONS
fix 1 1 1 1 0 0 0
fix 2 1 1 1 0 0 0
fix 3 1 1 1 0 0 0
fix 4 1 1 1 0 0 0
fix 5 1 1 1 0 0 0
fix 51 1 1 1 0 0 0
fix 52 1 1 1 0 0 0
fix 53 1 1 1 0 0 0
fix 54 1 1 1 0 0 0
fix 55 1 1 1 0 0 0

# MATERIALS:
set Steel 2;
uniaxialMaterial Steel02 $Steel 500e6 2.e11 0.0001 18.5 0.925 0.15 0.04 1.0 0.04 1.0;

# PLATE SECTIONS AND MATERIALS
# Concrete fc ft fcu epsc0 epscu epstu stc
nDMaterial PlaneStressUserMaterial 3 40 7 30e6 4e6 -30e6 -0.0025 -0.0035 0.1 0.08;
# nDMaterial PlateFromPlaneStress $matTag $PlaneStressMatTag $OutOfPlaneShearModulus
nDMaterial PlateFromPlaneStress 4 3 14.33e9; #
# Rebar
# Rebars Y
nDMaterial PlateRebar 11 $Steel 90
# Rebars X
nDMaterial PlateRebar 12 $Steel 0

section LayeredShell 1000 11 4 0.0175 11 0.0025 4 0.0175 11 0.0025 4 0.0175 4 0.0175 4 0.0175 4 0.0175 4 0.0175 11 0.005 4 0.0175


#PLATE ELEMENTS
element ShellMITC4 1 1 2 7 6 1000
element ShellMITC4 2 2 3 8 7 1000
element ShellMITC4 3 3 4 9 8 1000
element ShellMITC4 4 4 5 10 9 1000

element ShellMITC4 5 6 7 12 11 1000
element ShellMITC4 6 7 8 13 12 1000
element ShellMITC4 7 8 9 14 13 1000
element ShellMITC4 8 9 10 15 14 1000

element ShellMITC4 9 11 12 17 16 1000
element ShellMITC4 10 12 13 18 17 1000
element ShellMITC4 11 13 14 19 18 1000
element ShellMITC4 12 14 15 20 19 1000

element ShellMITC4 13 16 17 22 21 1000
element ShellMITC4 14 17 18 23 22 1000
element ShellMITC4 15 18 19 24 23 1000
element ShellMITC4 16 19 20 25 24 1000

element ShellMITC4 17 21 22 27 26 1000
element ShellMITC4 18 22 23 28 27 1000
element ShellMITC4 19 23 24 29 28 1000
element ShellMITC4 20 24 25 30 29 1000

element ShellMITC4 21 26 27 32 31 1000
element ShellMITC4 22 27 28 33 32 1000
element ShellMITC4 23 28 29 34 33 1000
element ShellMITC4 24 29 30 35 34 1000

element ShellMITC4 25 31 32 37 36 1000
element ShellMITC4 26 32 33 38 37 1000
element ShellMITC4 27 33 34 39 38 1000
element ShellMITC4 28 34 35 40 39 1000

element ShellMITC4 29 36 37 42 41 1000
element ShellMITC4 30 37 38 43 42 1000
element ShellMITC4 31 38 39 44 43 1000
element ShellMITC4 32 39 40 45 44 1000

element ShellMITC4 33 41 42 47 46 1000
element ShellMITC4 34 42 43 48 47 1000
element ShellMITC4 35 43 44 49 48 1000
element ShellMITC4 36 44 45 50 49 1000

element ShellMITC4 37 46 47 52 51 1000
element ShellMITC4 38 47 48 53 52 1000
element ShellMITC4 39 48 49 54 53 1000
element ShellMITC4 40 49 50 55 54 1000

# OUTPUTS
set Outputs Outputs
file delete -force Outputs
file mkdir $Outputs;
recorder Node -file $Outputs/disp28.txt -time -node 28 -dof $dof disp
recorder Node -file $Outputs/nodesdisp.out -time -nodeRange 1 56 -dof 1 2 3 4 5 6 disp

file mkdir $Outputs/Strain
file mkdir $Outputs/Stress

foreach ele {23} {
foreach gp {1} {
foreach fb {1 2 10 11} {
recorder Element -file $Outputs/Strain/strain$ele$gp$fb.txt -time -ele $ele material $gp fiber $fb strains
recorder Element -file $Outputs/Stress/stress$ele$gp$fb.txt -time -ele $ele material $gp fiber $fb stresses
}
}
}


# DISPLACEMENT CONTROL
pattern Plain 1 Linear {
sp $nsp $dof $dU
}

constraints Penalty 1.0e20 1.0e20
numberer RCM
system BandGeneral
test NormDispIncr 1.0e-7 50 2
algorithm KrylovNewton
integrator DisplacementControl $nsp $dof $dU
analysis Static
analyze 250

[imurdereri]

Yeah, i have the same problem like a year ago

This element or material CANT be used for purshover analisys but rarely for cyclic analisys you can get good results.