The using of „technical materials” speeded up lately. Because of this, parts are being designed from plastic, which have to sustain extreme stresses. The proper definition of material qualities is expensive; despite in every phase of designing, we need it to be done perfectly. In every industrial section it is important to work with exact material qualities, especially areas where there are strict safety rules (in connection with the lifespan). In this work we will introduce how to design suitable fatigue stress for the plastic samples and how to define the fatigue qualities of the various materials of Rapid Prototyping. This information could be important to change damaged equipments and parts in the military. Due to this, we performed the design of fatigue tests to help the designers elaborate military, safety improvements and proper renewing technologies.