FEAP User Forum
FEAP => Programming => Topic started by: Juan on March 18, 2013, 05:00:29 PM
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Hello All,
I am new working with FEAP modeling simple viscoelasticity on a 2D mesh of 4x4 square elements with a constant stress applied on one side and restrained on the opposite side.
I have written the Input script below but the values of displacement and stress I obtain on the output are the same for all the time steps.
I have checked the values of “qi” (Viscoelastic Strain) as they enter the subroutine “viscoe.f” (../feap83dist/ver83/elements/material/small/viscoe.f) and they are always zero for all the time steps. I have also tried with different time steps and loop sizes.
Any suggestions to obtain actual viscoelastic behavior?
Thank you so much,
Juan G.
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FEAP * * Example_Viscoelasticity
25 16 1 2 2 4
MATErial,1
SOLId
PLANe STRAin
ELAStic ISOTropic 200.0e9 0.4
VISCoelastic term1 0.7 10
! Blank termination record
COORdinates ALL
1 0 0 0
2 0 0.25 0
3 0 0.5 0
4 0 0.75 0
5 0 1 0
6 0 0 0.25
7 0 0.25 0.25
8 0 0.5 0.25
9 0 0.75 0.25
10 0 1 0.25
11 0 0 0.5
12 0 0.25 0.5
13 0 0.5 0.5
14 0 0.75 0.5
15 0 1 0.5
16 0 0 0.75
17 0 0.25 0.75
18 0 0.5 0.75
19 0 0.75 0.75
20 0 1 0.75
21 0 0 1
22 0 0.25 1
23 0 0.5 1
24 0 0.75 1
25 0 1 1
! Blank termination record
ELEMents
1 1 1 1 2 7 6
2 1 1 2 2 3 8 7
3 1 1 3 4 9 8
4 1 1 4 5 10 9
5 1 1 6 7 12 11
6 1 1 7 8 13 12
7 1 1 8 9 14 13
8 1 1 9 10 15 14
9 1 1 11 12 17 16
10 1 1 12 13 18 17
11 1 1 13 14 19 18
12 1 1 14 15 20 19
13 1 1 16 17 22 21
14 1 1 17 18 23 22
15 1 1 18 19 24 23
16 1 1 19 20 25 24
! Blank termination record
BOUNdary restraints
1 0 1 1
6 0 1 0
11 0 1 0
16 0 1 0
21 0 1 0
! Blank termination record
FORCes
5 0 2.5e6 0.0
10 0 5.0e6 0.0
15 0 5.0e6 0.0
20 0 5.0e6 0.0
25 0 2.5e6 0.0
! Blank termination record
END
BATCh
DT,,1
TRANsient BACK
LOOP,,2
TIME
LOOP,,10
TANG,,-1
OUTP TANG
TANG,,1
NEXT
DISP ALL
STREss ALL
NEXT
END
STOP
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The viscoelasticity seems to be working fine. I have modified your input file to generate a time history file of the displacement of node 5 (dof 1). Run the file and it will generate a file Pvisc*.dis. Plot the first column time versus the second column ux @ node 5 and you will see that it is ok.
Note two changes. One I changed the time integrator to Newmark which makes better sense than backward Euler for a mechanics problem. Two your mesh had one element (element 2) with five nodes so I fixed that.
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Dear FEAP community,
I think I have a similar issue, since I am not able to reproduce viscoelastic effect in FEAP8.3. I ran the same input file from the last post both in FEAP8.3 and in FEAPpv4.1, with the results shown in Fig.1 for the horizontal displacements of node 5. As you can see no creep effects are present in FEAP8.3. How could I fix the problem?
Thanks in advance,
Jacopo
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Post your input file.
Note that version 8.3 is very old -- you should consider updating to the latest version.
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Your version 8.3 is not reading the VISCOelastic material properties. Look in your output file and you should see that they are not being printed.
I note that in version 8.6 the syntax changed to VISCoelastic,DEVIatoic,#,# and
VISCoelastic,VOLUmetric,#,# but this should not be a problem with version 8.3.
You can debug what is going on by looking around line 1404 in elements/material/inmate.f (the routine that reads the material properties).
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Dear Professors,
thank you for your prompt response. Please find in the attachments both the input and the output files. Actually the VISCoelastic material set is red by the program and printed in the output file. I've tried debugging the line of code suggested by Prof. Govindjee, but I did not come to a solution.
Jacopo
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remove the transient Newmark command -- your problem has no mass, for a quasi-static problem you can use the defaults