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# non convergence for nonlinear analysis

## non convergence for nonlinear analysis

(OP)
Hello everyone,
I have simulated nonlinear characteristics of sandwich composite subjected to three points bending. But I have theses two questions.
1) how to solve this problem that is numerical singularities at one node. Besides, this warming seem on effect other iterations, how come?

2) how to solve this question which are 8 negative eigenvalues. Besides, the error is show that too many attempts made for this increment. I cannot sure whether the negative eigenvalues cause this error.

### RE: non convergence for nonlinear analysis

A singularity usually indicates a possible rigid body motion of the part in the mentioned DOF. If it is at the beginning and it disappears, then it probably was a open contact state.

Negative eigenvalue are usually caused by a loss of stiffness or solution uniqueness, either in the form of a material instability or the application of loading beyond a bifurcation point (buckling). When the analysis converges in further iteration and the results look plausible, then they can be ignored.

You should not only look at the messages, but also what is happening in the equilibrium calculations (Residuals tab). How to read that is explained in the 'Nonlinearity' section of the Getting Started Manual.

### RE: non convergence for nonlinear analysis

(OP)
Sincerely thank you @Mustaine3 for your kind help.

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