[Geoqus] Questions about viscoplasticity

[Frank Richter]

try
https://groups.yahoo.com/group/ABAQUS

and imechanica.org

Good luck

Frank



Am 2015-08-11 08:57, schrieb Chris Salomon:
> Dear GEOQUS Members,
> 
> 
>  I have some questions related to the theory of viscoplasticity.
> Maybe there's someone here who can help me.
> 
> 
>  I wrote an UMAT for a (at this moment simple) viscoplastic model.
> But I'm not sure if everything is correct.
> 
> 
>  I use the Return Mapping algorithm by Simo and Hughes (1998,
> Computational Inelasticity, Box 3.8 (P. 156) in combination with Box
> 3.5 (P. 159)). Therefore it seems as if I can simply replace the
> consistency parameter (lambda) for the plastic regime with its
> counterpart in the viscoplastic regime (p). I.e. I currently use
> Perzyna's model (1966, Fundamental Problems inviscoplasticity, Rec.
> Adv. Appl. Mech. 9) for which I set
> 
>  p=1/Viscosity*(f/Yield)^N
> 
>  whereas f is the yield-function and Yield the corresponding
> yield-stress. The viscoplastic strain-rate therefore becomes
> 
>  de_(vp)=p*df/d(stress).
> 
>  Questions:
> 
>  1. Can I simply replace the consistency parameter with p and still
> use  the algorithm out of Box 3.5 from Simo and Hughes? (I also want
> to include isotropic and kinematic hardening!)
> 
>  2. Is my definition of p correct? Because p now has the units
> 1/(Pa*s) but I would expect it to be 1/s.
> 
>  3. I want to model subduction zones with this but am not sure if I
> should use an associative or non-associative flow-law. What do you
> think is better? For example Fossum and Brannon (2004, The SANDIA
> GeoMode: Theory and User's Guide) use non-associative flow-laws
> according to the works by Miller and Cheatham (1972, A new yield
> condition and hardening rule for rocks, Int. J. Rock Mech. Min. Sci.
> 9).
> 
> 
>  I would really appreciate it if someone could help me.
> 
>  Greetings
>  Chris Salomon
> 
> 
> 
>  PS. For a review see e.g. Chaboche (2008, A review of some
> plasticity and viscoplasticity constitutive theories, Int. J. Plas.
> 24).
> 
>  PPS. A much simpler version of the Return Mapping Algorithm can be
> found in Zeng et al. (1996, Numerical implementation of constitutive
> integration for rate-dependent elastoplasticity, Comp. Mech. 18).
> 
> 
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