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FAQ 002992 EN

24 April 2019

Frank Faulstich Calculation RFEM

How does the calculation of models with plastic materials work?


Finite elements with plastic material are divided into 10 layers. First, a normal elastic analysis is performed in the first iteration. Then, the stress in each element is calculated according to the set strength hypothesis in each individual layer. If the limit stress in one of the layers is exceeded, the stiffness of this layer is reduced. Based on the reduced stiffnesses of the 10 layers, an overall stiffness is determined for each element. With this new stiffness, we start a new calculation iteration.

Iterates until the changes are only small.

The total stress is converted into the stresses of the individual layers by means of the laminate theory. This theory is also applied for the conversion between the stiffnesses of the layers and the total stiffness.

4 different strength models can be used as the limit stress:

  • Shape Change Energy Hypothesis (von Mises-tension)
  • Shear stress hypothesis (Tresca stress)
  • Failure hypothesis according to Drucker-Prager
  • Failure hypothesis after Mohr-Coloumb

The choice of the failure hypothesis is shown in Figure 1.

The von Mises hypothesis is preset because it is the most frequently used strength theory.


Strength Hypothesis Nonlinear material model

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