The main purpose of this paper is monitoring propagation of plastic area of fatigue crack.There were made notch on specimens and they were cyclically loaded with three-point bending.The record was evaluated after a certain number of loading cycles.The loading force is still constant throughout the measurement time for all specimens.The whole process was recorded using an infrared camera.

This work is supported by: VEGA 1/0795/16 Development of effective methods for correction and optimization of coupled mechanical system and KEGA 017ŽU-4/2017 Dynamics solved in programs MATLAB and MSC.ADAMS