[Geoqus] Byerlee / creep law in Abaqus

[Susan Ellis]

Hi again Kaspar

The way I'm getting around the problem with the creep limit
in plasticity is to set the friction angle to zero,
and to use a dependency on the DRUCKER PRAGER HARDENING
lines which basically increases the 'cohesion' as a function
of (sign)tan(phi), where phi is my desired friction angle
- I compute (sign) in user subroutine USDFLD

eg:

*DRUCKER PRAGER, SHEAR CRITERION=LINEAR,DEPENDENCIES=1
0.01,1.00,0.01,,.00E+00
0.01,1.00,0.01,,.10E+10 (ie essentially these lines not used)
*DRUCKER PRAGER HARDENING,DEPENDENCIES=1
.15E+07,0.,,.00E+00
.10E+10,0.,,.10E+10  (adjust this last figure to match p at which
                      (sign)tan(phi)+cohesion = 1e+09;
                      then return p from subroutine USDLFD)
*DRUCKER PRAGER CREEP,LAW=STRAIN
.10E-39,3.10,0.00,   0.00
.10E-39,3.10,0.00, 170.00
.21E-39,3.10,0.00, 180.00
.45E-39,3.10,0.00, 190.00
.93E-39,3.10,0.00, 200.00
. (lots of lines here, compute Aexp(-Q/RT) depending on creep law
. and increment T every 10 degrees- note T is in celsius here,
. but T in creep equation is in Kelvin)
.
.
.93E-39,3.10,0.00, 630.00

cheers
Susan


Dr Susan Ellis
Institute of Geological and Nuclear Sciences
Gracefield Rd, PO Box 30368
Lower Hutt
New Zealand
S.Ellis at gns.cri.nz
ph (home): 0064-4971-5024
ph (office): 0064-4570-4730
fax (office): 0064-4570-4600


On Wed, 12 Nov 2003, Kasper Fischer wrote:

> Hi Susan,
> 
> thank you for your answer. I will try to introduce this in my model. I
> just have one more question:
> Are You using temperatur dependent friction angles or hardening parameters?
> The reason why I ask this is because the Abaqus theory manual shows a
> picture (Fig. 4.4.2-7) of a region where no creep is active in the
> p-q-plane (a cone below the line p tan \beta). Therefore I would have to
> decrease \beta to small values at high p (=depth, high T) to have creep
> at low q for high p. Is this right?
> 
> Maybe you can post the *DRUCKER PRAGER, *DRUCKER PRAGER HARDENING, and
> *DRUCKER PRAGE CREEP (truncated)  lines of an example.
> 
> cheers,
> 
> Kasper
> 
> Susan Ellis wrote:
> 
> >Hi Kaspar
> >
> >You can use *DRUCKER PRAGER CREEP
> >and put in a temperature dependency there.
> >I have a long list of A*exp(-Q/RT), n, 0, T
> >values following this line. It works quite well
> >and gives a smooth brittle-ductile transition zone
> >
> >cheers,
> >Susan
> >
> >Dr Susan Ellis
> >Institute of Geological and Nuclear Sciences
> >Gracefield Rd, PO Box 30368
> >Lower Hutt
> >New Zealand
> >S.Ellis at gns.cri.nz
> >ph (home): 0064-4971-5024
> >ph (office): 0064-4570-4730
> >fax (office): 0064-4570-4600
> >
> >
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> >
> 
> -- 
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> | Dr. Kasper D. Fischer             <kasper.fischer at ruhr-uni-bochum.de> |
> | Ruhr-Universität Bochum                                               |
> | Institut für Geologie, Mineralogie und Geophysik                      |
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