Study on nonlinear damping properties of foamed Al

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.