Plastic is not a soft steel! This simple rule applies particularly in showing failure. The chemical structure of the polymers made from long-chain macromolecules makes the performance of the plastics very different when subjected to compression and tension. Despite comparable stress conditions, the plastic can withstand considerably higher energies under pressure than under tension. The same applies for loads along and at right angles to the fiber direction: plastic fails in terms of anisotropy! Another effect is the dependence on the strain rate. Just as the stiffness is changed by the load rate, failure also shows a clear dependence. Simple failure models known from the metal range, e.g. according to von Mises, must inevitably fail here. These effects and additives that change the toughness require a special numerical handling of the failure tailored to the plastic. The numerical description of the material used in ULTRASIM® is able to show these important effects accurately.