Improve convergence rate and robustness of your finite element simulation.
It is a widely accepted notion that good convergence (or any convergence at all) is difficult to achieve in a progressive failure simulation of a composite structure. In fact, many progressive failure simulations terminate early, not due to global structural failure, but rather due to the inability of the finite element code to obtain a converged solution at a particular load increment. Helius PFA significantly improves the overall convergence rate and robustness of finite element simulations of progressive failure of composite structures. Experienced users of Abaqus/Standard are no doubt familiar with the code's tendency to reduce (or cut-back) the time increment size when the code senses that convergence is difficult to achieve. However, when Helius PFA is used in conjunction with Abaqus/Standard to perform a progressive failure analysis, the increased robustness of the solution greatly diminishes the need for time incrementation reductions (or cut-backs), thus the analysis can be completed much faster than without the use of Helius PFA. 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 Abaqus/Standard. These changes can be enacted using the *CONTROLS keyword statement.
In Abaqus/Standard, the default settings for the nonlinear solution process are based on the fundamental assumption of the Newton-Raphson algorithm that the nonlinear response of the composite structure is sufficiently smooth at both the local and global levels. However, in a progressive failure simulation of a composite structure, the nonlinear response of the composite structure is not smooth, especially at the local level, and it is this situation that is primarily responsible for the difficulty in obtaining convergence. Helius PFA is specifically designed to efficiently handle this localized "jagged" material response; however, the default settings of Abaqus/Standard must be changed in order to allow Helius PFA to improve the convergence characteristics of the finite element simulation. These default settings can be changed via the data line of the *CONTROLS keyword statement. In this case, the data line of the *CONTROLS keyword statement is used to significantly increase the number of equilibrium iterations that Abaqus/Standard will perform before the code evaluates the need for a reduction (or cut-back) in time step size.
The specific data and options that are used with the *CONTROLS keyword statement is discussed later (Step Modifications for Abaqus/Standard Analyses and Nonlinear Solution Control Parameters). For now, it suffices that you are aware that the *CONTROLS keyword statement is used to provide Helius PFA with the freedom to drastically improve the speed and robustness of convergence in progressive failure simulations.