Fusheng Han

Damping behavior of foamed aluminum

Damping measurements were performed to examine the damping behavior of foamed aluminum (FA). It was found that the damping capacity of FA is higher than that of its parent metal, and the major contribution of pores to the damping of the material is to raise the internal friction background, particularly at elevated temperatures. The damping mechanisms can be interpreted by the nonuniform stress and strain distributions originating from the inhomogeneous pore structure morphology, the number of boundaries formed by the pores, the high density of defects, and their movement and interaction.

Internal friction of foamed aluminium in the range of acoustic frequencies

The internal friction of aluminium foams with various porosities was measured in the range of acoustic frequencies over a wide strain-amplitude range by the bending-vibration method. The measured internal friction shows that aluminium foams have a damping capacity which is enhanced in comparison with bulk aluminium, increases with increasing porosity, decreases with increasing frequency and increases with increasing strain amplitude. In order to explain the behaviour of the internal friction, a mechanism of internal dissipation energy was presented, and an approximate expression for internal friction is derived which is based on the equations of plane waves in elastic material with voids. This expression can account for the dependence of the internal friction on porosity, pore size and frequency. To gain further insight into the dependence of the internal friction on amplitude, the non-linear characteristics of oscillations were observed, and it was found that the resonance curves are asymmetric and the resonant frequencies are proportional to the square of amplitude with a negative slope. On the basis of the equations of the motion and the experimental results, the non-linearity of oscillations was ascribed to a non-linear damping term and an approximate expression for the damping coefficient with respect to amplitude was obtained.

Low-frequency internal friction of foamed Al

Abstract The low-frequency damping properties of foamed Al have been studied. The internal friction of foamed Al obviously increases with an increase in porosity and a decrease in pore size, is nearly independent of frequency and typically depends on strain amplitudes. Based on the observed experimental phenomena, a damping mechanism is presented. According to the damping mechanism, the effects of pores and strain amplitude on internal friction have been analysed in detail and the experimental results have been better explained.

Study on nonlinear damping properties of foamed Al

Abstract The nonlinear damping properties of foamed aluminium were investigated by the bending and vibration method. The experimental results show that foamed aluminium Al possesses some nonlinear properties, that is, the internal friction increases with increase in strain amplitude, the resonance curve is asymmetric and the resonant frequency is approximately proportional to the square of strain amplitude. These nonlinear properties are enhanced with increase in porosity and decrease in pore size. The analysis was performed using the equation for forced oscillation under friction. The nonlinearity of foamed aluminium may result from the nonlinear damping term, which is related not only to the velocity but also to the displacement. The nonlinear damping coefficient increases with increasing porosity and decreasing pore size.

Nonlinear Internal Friction Character of Foamed Aluminum

An experiment has been carried out to investigate the damping behavior of foamed aluminum. It was found that foamed aluminum has a significant nonlinear internal friction character, i.e., its damping capacity is amplitude-dependent, and this character tends to be more pronounced with decreasing the density and pore size.