[CIG-SHORT] "Runtimeerror Infeasible stress state" - cannot project back to yield surface.

[Charles Williams]

Hi Xiao,

This sort of behavior can happen when you have tensile pressure conditions.  It typically means that you are past the point of the cone of the DP yield envelope.  There is an option that allows you to project back to a tensile stress state (see the manual); however, this sort of stress state should not generally arise in a quasi-static tectonic simulation, since gravity will always provide a compressive stress state.

Cheers,
Charles


On 15/05/2014, at 4:49 pm, Ma, Xiao <xiaoma5 at illinois.edu> wrote:

> Hi, 
> I am running a simulation using Druckerprager elstoplastic model, when I run the code, I get the following error 
> "Runtimeerror Infeasible stress state" - cannot project back to yield surface.
> Here is how I wrote the plastic material part :
> 
> [pylithapp.timedependent]
> 
> materials = [plastic]
> 
> [pylithapp.timedependent.materials]
> 
> 
> 
> 
> 
> elastic = pylith.materials.DruckerPragerPlaneStrain
> 
> 
> 
> [pylithapp.timedependent.materials.plastic]
> 
> 
> 
> # Label for material
> 
> label = Plastic material
> 
> 
> 
> # Nodeset id from CUBIT
> 
> id = 1
> 
> 
> 
> # Spatial database with physical properties for elastic material
> 
> db_properties.label =Plastic properties
> 
> db_properties.iohandler.filename = matprops.spatialdb
> 
> 
> 
> # Set the basis functions and quadrature:
> 
> # 2-D Lagrange cell with 2nd order quadrature
> 
> quadrature.cell = pylith.feassemble.FIATLagrange
> 
> quadrature.cell.dimension = 2
> 
> quadrature.cell.quad_order = 2
> 
> ************************************
> 
> And This is the material database I am using .
> 
> #SPATIAL.ascii 1
> 
> SimpleDB {
> 
> // number of physical properties
> 
> num-values = 6
> 
> 
> 
> // Names and units of physical properties
> 
> value-names = density vs vp friction-angle cohesion dilatation-angle // names of the material property values
> 
> value-units = kg/m**3 m/s m/s degree kPa degree // units
> 
> 
> 
> // Number of locations where physical properties are given
> 
> // 1 location -> data is uniform -> data dimension is 0
> 
> num-locs = 1
> 
> data-dim = 0
> 
> 
> 
> // Problem is in 2-D
> 
> space-dim = 2
> 
> 
> 
> // Coordinate system (2-D with coordinates in meters)
> 
> cs-data = cartesian {
> 
> to-meters = 1.0
> 
> space-dim = 2
> 
> }
> 
> }
> 
> // Columns are x, y, density, vs, vp
> 
> 0.0 0.0 2500.0 3000.0 5291.502622129181 30.0 50.0 30.0
> 
> 
> 
> Best,
> 
> XIao
> 
> 
> 
> 
> 
> 
> _______________________________________________
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Charles A. Williams
Scientist
GNS Science
1 Fairway Drive, Avalon
PO Box 30368
Lower Hutt  5040
New Zealand
ph (office): 0064-4570-4566
fax (office): 0064-4570-4600
C.Williams at gns.cri.nz

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