Crystal Plasticity Modelling

Hi all,

     I want to set up a critical shear strain - normal stress criterion, in UMAT by prof. Huang. For the strains it is easy to get a critical strain along a slip plane; but for the stresses the notation is quite weird. It is not the same! See below:

C       Array STATEV:

C       3*NSLPTL+1 - 6*NSLPTL  :  current components of normals to slip

C                                 slip planes

C       6*NSLPTL+1 - 9*NSLPTL  :  current components of slip directions

CCFIX    9*NSLPTL+1 - 10*NSLPTL :  total cumulative shear strain on each

CFIX                              slip system (sum of the absolute

CFIX                              values of shear strains in each slip

CFIX                              system individually) 

So by using the 9*NSLPTL+1 - 10*NSLPTL we can get the critical strain along a plane; and the specific directions and normals by 6*NSLPTL+1 - 9*NSLPTL, 3*NSLPTL+1 - 6*NSLPTL.

But for the stresses it doesn’t give any relation between the slip systems and directions with stress components.

C-----  Update the stress: STRESS

C NTENS :: total nr of stress components (direct + shear components)

      DO I=1,NTENS

         STRESS(I)=STRESS(I)+DSTRES(I)-DSOLD(I)

      END DO

Could it be that the sample reference system is used? In any case it seems that the stresses acting on a slip system cannot be resolved!

All the best,

             Panos