Modify the solution control parameters using a text editor.
It is widely accepted that good convergence (or any convergence at all) is difficult to achieve in progressive failure simulations of composite structures. In fact, many progressive failure simulations terminate early, not due to global structural failure, but simply due to the inability of the finite element code to obtain a converged solution at a particular load step. One of the major advantages of Helius PFA is that it has been optimized to significantly improve the overall convergence rate and robustness of progressive failure simulations of composite structures. However, in order to take full advantage of the superior convergence characteristics, you must change some of the default settings that govern the nonlinear solution process used by ANSYS. These changes can be enacted using the NROPT, PRED, NSUBST, CNVTOL, and NEQIT commands.
Regardless whether the SOLCONTROL command is ON (default) or OFF, you will need to override these nonlinear solution control parameters.
The NROPT command is used to do two things: a) instruct ANSYS to use the 'Full' Newton Raphson algorithm, and b) prevent ANSYS from using their 'Adaptive Descent' algorithm to help the solution process. An example of the NROPT command fulfilling these two requirements is shown below.
NROPT, FULL, , OFF
In ANSYS, the nonlinear solution process is based on the fundamental assumption of the Newton-Raphson algorithm that the nonlinear response of the composite structure is sufficiently smooth at both the global and local levels. However, in a progressive failure simulation of a composite structure, the nonlinear response of the composite structure is not smooth. This is especially true at the local level where material failure results in an instantaneous reduction of material moduli. This non-smooth material response is one of the primary factors responsible for the difficulty in obtaining convergence in progressive failure simulations. Helius PFA's method of managing material nonlinearity is specifically designed to handle this localized non-smooth material response. However, the default settings of ANSYS' nonlinear solution control parameters must be changed to allow it to improve the convergence characteristics of the finite element simulation.
CNVTOL, F, , , 0
NEQIT, 1000