The fatigue strength of 40X steel at 25 oC was determined following ASTM E606M standard for strain-controlled tests. The studied experimental dependence was modelled with a power function as well as with the functions and coefficients described in the standard. The material expresses plastic properties for cyclic loadings above 0.2% strain amplitude.
The influence of registered signals smoothing on the calculated diagram of the test specimen was analysed for impact test using split Hopkinson-Kolsky pressure bar. Two methods are used to smooth the signals: low-pass filtering built into the software and arithmetic mean averaging. When determining the elastic modulus and the upper yield stress in these high-strain rate tests, it is concluded that more accurate values are obtained by filtering with a cut-off frequency in the range of 60 to 80 kHz. For the second method, it is concluded that it is best to average the curves with an amplitude of 3 or 4 microseconds. Attention is paid to the correct ch oice of the initial moments from which the reading of the signals begins because the wrong choice leads to inaccurate calculations and conclusions about the properties of the tested material.