The investigation of dynamic properties of 3D-printed steel parts

Additive technologies are promising for manufacturing parts of metal navigation devices with complex shapes. Finite element analysis is used during the designing of such items. The modeling accuracy is determined by the correctness of the specified physical properties of materials. The properties of materials used in 3D printing significantly differ from the ones used in the traditional manufacturing. Researchers focus on such characteristics as Young's modulus, Poisson's ratio, hardness and strength. Meanwhile, some applications require dynamic properties. The paper presents the investigation and comparison of damping properties of three steel parts produced by different methods. The first part is manufactured by 3D printing with melting in the transverse direction, and the second part is done by melting in the longitudinal direction, while the third one is traditionally manufactured. The parts are shaft shaped with constant cross-section and have the same geometric dimensions. The TIRA TV 5220 / LS-120 stand is used. A piezoelectric accelerometer is installed at the loose end of the part. The tests are carried out in the frequency range from 15 to 3500 Hz and with an acceleration of 19.6 m/s2 (2 g). The accelerometer output is used to calculate the damping coefficient. The results are verified by comparison with the finite element modeling results. The damping coefficients of transverse and longitudinal 3D-printed parts are 0.022 and 0.006, respectively. The damping coefficient of the traditional manufactured part is 0.023. The difference of 3D-printed parts damping coefficients can be explained by the denser fusion of powder granules when printing one layer than between layers. In this case, a crystal structure with greater rigidity in the printing plane is formed and it limits the dissipation of vibrati on energy due to internal friction. Finite element modeling shows mismatch between the experimental and calculated values of the printed parts natural frequencies. Considering that the values of natural frequencies are largely determined by Young's modulus, a parametric optimization of its value is carried out. It was found that the value of Young's modulus does not correspond to the values determined during tensile tests for similar samples. Thus, 3D-printed parts have different vibration and static stiffness. This is not typical for metals and should be taken into account in simulations. The research results can be used in the simulation model development of steel 3D-printed parts and in the design of digital twins for navigation devices. It allows one to estimate vibration resistance of promising products at the early stages of their design and to optimize the construction minimizing