PERMAS-NLS Nonlinear Statics

Geometrically nonlinear behavior

This module part allows for the geometric nonlinear analysis of models. There, large displacements with small strains (i.e. linear elastic material behavior) are assumed. Beside an automatic load step control different nonlinear solvers are available (like Newton-Raphson, Modified Newton-Raphson, Quasi Newton BFGS, Secant Newton, Line search, Arc length method).
The nonlinear characteristic may be represented by xy-plots, where the load increments can be chosen automatically or manually.

Material nonlinearities

This part of the module allows the analysis of nonlinear material behaviour of models with small strains:

• Nonlinear elasticity (of Cauchy type)
• Plasticity (von Mises, Tresca, Drucker-Prager, Mohr-Coulomb)
• Creep with
  • nonlinear elasticity or
  • plasticity

The material can be defined temperature-dependent for Young's modulus, yield stress, and the stress-strain curves. A time-dependent characteristic is present for creep calculations in addition. Hardening in plasticity can be defined isotropic or kinematic (or mixed).

For the use of shell elements with material nonlinearities, an element family of elements with a 3-dimensional shell formulation is available, which is applicable for linear analyses, too. This element family (triangles and quadrangles with linear and quadratic shape functions) has been designed for nonlinear analysis with already existing shell models.

Nonlinear NAFEMS Test

For the modeling of gaskets a family of gasket elements is available. These elements are used to define the nonlinear behavior in a preferential direction by a measured force-displacement curve of the real gasket.

An incremental and iterative solver strategy is based on Newton-Raphson, Modified Newton-Raphson, and Quasi-Newton method. An automatic load step control allows for an optional specification of initial load step and total applied load (or time). The material laws may be defined either in tabular form or as user-written subroutine (Fortran or C).

Combination of material and geometrical nonlinearities

Analyses with material nonlinearities can take into account the geometrical nonlinear effects, too. There, also follower loads like pressure loads, temperature loads, and inertia loads can be taken into account.

Generals

In case of contact definitions the nonlinear analysis takes them into account automatically performing a nonlinear contact analysis.

Pressure of cylinder head gasket

Initial states like for rotating structures can be taken into account in nonlinear analyses.

The results of a nonlinear analysis may be used for subsequent analysis like a dynamic mode analysis.

In many cases, the major part of the model is linear. This is an ideal prerequisite to apply substructure technique, where the linear parts are put in subcomponents and all nonlinear parts are put in the top component. This procedure will lead to a significant reduction in run time.