there are many scientific articles describing the weld test, e.g. hardness, tensile tests. the weld structure can be examined by optical microscopy and scanning electron microscopy. the computer finite element method (fem) is used to predict the shape of the flash and interface, not only for rotary friction welding (rfw), but also for friction stir welding (fsw), linear friction welding (lfw), friex and others. temperature measurements are also carried out for scientific purposes. for example, temperature may reduce material properties, (e.g. dynamic recrystallization will occur).