Micro-mechanism of damping vibration attenuation on porous metal coating

Based on molecular dynamics method and in-situ scanning electron microscopy (SEM) observations, the damping efficiency of the porous metal coating is discussed in this paper. Molecular dynamics simulation is performed to study the plastic deformations of Cu films with vibration. In the simulation, embedded atom method (EAM) is selected and in the method an interatomic potential function is used. And porous copper coating is carried out for calculating by using velocity-verlet algorithm. The plastic deformation is due to the dislocation nucleation near free surfaces, and the dislocation is shaped into forward emission in the < 110 > crystal orientation near the defects. At the same time, the change curves of stress and strain are drawn by origin software. Damping factor (eta) is calculated by using the time of strain lagging stress. The regulation of elastic potential energy attenuation is obtained by energy calculation. On the other hand, in-situ tensile/compression experiment is conducted by the FEI Quanta 200 SEM with a maximum load capacity of 2 kN at room temperature. A copper layer is deposited on the surface of the polyimide film by the electron beam evaporation deposition method. The thickness of the copper layer is 10 mu m and the thickness of polyimide is 175 mu m. Using the scanning electron microscope, microstructures of the coating are observed. It could be seen that the coating and the polyimide film are both better in compactness. Using in-situ testing machine at SEM, the samples with and without copper coatings are respectively tested under tensile and unloading. The rate of displacement loading is 2 mm/min, the results of load (F) and displacement (l') are printed every 0.1 s. The loading direction is horizontal. During in-situ tensile/compression test, the straining is stopped several times in order to make the observations and take micrographs. The digital SEM images are directly transferred to a computer via a direct memory access type A/D converter, which can rapidly capture clear images of the 1024 x 943 pixel frames. The simulations and experimental results indicate that the dislocation near defects get rid of weak pinning points and limit to the strong pinning point, the internal friction is generated due to the change of dislocation and the relative sliding near grain boundary, and the stored elastic potential energy is consumed, which causes the damping effect of the film.