Theoretical And Experimental Study On SMA Damper And Magnetic Vibration Absorber Under Random Excitation

Attention is focused on designing new types of damper made of Shape Memory Alloy (SMA) and rare-earth magnets (NdFeB) in vibration suppression of a mobile platform, which is under stochastic environmental loading.The main problem that superelastic SMA was used in random vibration control is its deficient damping capacity. To overcome this, a new craft of making Pseudo-rubber Metal is introduced in designing SMA damping element. The damping element is made of SMA wire which undergo special procedures including winding, weaving and mould pressing etc. Test results show that the maximum recovery deformation of SMA Pseudo-rubber Metal can reach 30% and SMA damper composed of two Pseudo-rubber Metal elements has a good performance in the random vibration control (its damping ratio coefficient can even reach above 0.5). RMS of system acceleration response can be reduced by more than 70% with the damper.It is found from experiment results that precompression has influence on SMA Pseudo-rubber Metal damper's hysteresis characteristic. Based on the phenomena, a theoretical system on optimization design of nonlinear damper is established in the dissertation. The theory mainly concentrates on the role of prestress including precompression and pretension in designing nonlinear damper, and has huge potential use in practical engineering.With an advantage that the motion equation of the system can be linearized directly in closed form, a simple superelastic model for SMA was proposed in the equivalent linearization method. The method was employed to predict response of SMA superelastic system under stationary white noise excitation. It was finally concluded that the equivalent linearization method based on our model can be used in engineering with higher computation efficiency.For easy computation in stochastic response, Bouc-Wen model is selected to describe SMA Pseudo-rubber damper's hysteresis characteristic.In order to improve the performance of single type magnetic vibration absorber under random excitation, this dissertation proposes an application of dual magnetic vibration absorber made of Rare-earth magnets (NdFeB). Test results show the dual magnetic vibration absorber has good performance not only to harmonic excitation but also random one. By use of dual magnetic absorber with a small mass ratio (μ=0.066), system's acceleration response is decreased to 14.3% (harmonic excitation) and 16.93% (random excitation) respectively. Initial study about magnetic damping is also conducted.