pjoseph's blog

Hi there,

I am running into a problem where for a simple, 2D, axisymmetric, single element problem, I get a "singular" matrix for my stress.  Consequently my force equilibrium equations cannot be solved for the displacements at the nodes.

The principle stresses for the axisymmetric case are as usual, a 4x1 matrix sigma given as:

[sig1, sig2, tao, sig3]^T and obtained as:

[sigma]=[D][S][B3][u]

(my problem is that [D][S][B3] a 4x8 matrix for a four node axisymmetric element always comes out singular for the first load increment)