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Section & Integration Points in S4R elements. SIGINI RESIDUAL STRESS

Section & Integration Points in S4R elements. SIGINI RESIDUAL STRESS

Section & Integration Points in S4R elements. SIGINI RESIDUAL STRESS

(OP)
thread799-326356: Section & Integration Points in S4R elements.

Hello to everyone,

I am trying to introduce residual stress in the shell elements by SIGINI.
This thread is about Section Points and Integration Points notation in shell element and coordinate system.
To introduce residual stresses in the shell element through the thickness all I have to do is find the shell element node(NOEL), then section point in this node(KSPT) and then, set the stresses sigma(1)=... When I do like this I have not convergence problem. But the point is that I have to define different value of stress in the geometry and I did this with COORD(2) AND COORD(3) option.
First I find the shell element node(NOEL, then I define the zone where I would like to define the stress value with COORD(),then section point in this node(KSPT) and then, set the stresses sigma(1)=...
But due to COORD definition I have convergence problems and a lot of warning?
***WARNING: THE SYSTEM MATRIX HAS 1012 NEGATIVE EIGENVALUES.

NEGATIVE EIGENVALUES MEAN THAT THE SYSTEM MATRIX IS NOT
POSITIVE DEFINITE:
FOR EXAMPLE, A BIFURCATION (BUCKLING) LOAD MAY HAVE BEEN EXCEEDED.

How can I introduce different stress value in shell in diferent zone? How can I solve the convergence problem?

Regards,

Ane

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