Because of the importance of lightweight constructions, nowadays other materials are moreand more substituting components which had previously been made of metals. The usage ofshort fiber-reinforced plastics instead of metals seems self-evident in many cases becauseof their high specific strength and the favorable manufacturing processes. For fatiguelife prediction a simulation process was established, which takes into account the fiberorientation and distribution as a result of an injection molding simulation. Hypothesesfor fatigue life prediction of orthotropic materials have been derived from a lot of testson specimens, implemented in the standard fatigue software tool FEMFAT and verified so farwith component tests.