Investigation of the generation mechanism of squeal noise under non-negative damping conditions

The traditionally known generation mechanism of squeal noise is generally agreed to be the negative damping theory, which is represented by the negative slope of friction creepage curve. Recently, however, it was found that squeal noise still can be generated when the negative slope is eliminated. To investigate this phenomenon, water-based and oil-based friction modifiers are applied on a test rig to create non-negative damping conditions. The adhesion ratios at various rolling speeds are measured, and it is found that the negative slopes of friction curves can be eliminated when using friction modifiers, but squeal noise still exists. To investigate this phenomenon, a model involving the effect of vertical dynamics on squeal noise is developed in this research. The results show that the involvement of vertical dynamics has negligible effect on wheel vibration velocity when the friction creepage curve has a negative slope. When the friction creepage curve has a zero or positive slope, however, the results show that a stable lateral vibration still can be generated when vertical dynamics is involved. The generation mechanism of wheel squeal involving vertical dynamics is illustrated from the perspective of power input. Furthermore, the sound pressure levels of squeal noise are simulated using this model and the results correlate well with experimental measurements. Therefore, the results indicate that the vertical dynamics may be the reason why squeal noise still exists under non-negative damping conditions.

A Computational Method for Dynamic Analysis of Deployable Structures

A computational method is developed to study the dynamics of lightweight deployable structures during the motion process without regard to damping. Theory and implementation strategy of the developed method are given in this study. As a case study, the motion process of a bar-joint structure and a ring array scissor-type structure was simulated under external dynamic loading. In order to verify the effectiveness of the method, the simulation results are compared with the results predicted by the authenticated multibody system dynamics and simulation program. It shows that the method is effective to dynamic analysis of deployable structures no matter the structures are rigid or elastic. Displacement, velocity, and acceleration for the entire deployable structures during the motion process can be computed, as well as strain if the deployable structure is elastic.

Influence of HA and Environmental Factors to the Damping Performance of HA/Mg-3Zn-0.5Zr Composites

Vibration and noise are the dangers for equipment, human health and environment. Developing of a new Mg matrix composite with high damping performance and high strength rate has been acknowledged as an important approach for the reduction of vibrations and prevention of noise. In this paper, xHA/Mg-3Zn-0.5Zr (x=0.5wt.%, 1wt.%, 1.5wt.%) composites were prepared by vacuum induction melting and hot extruding. The microstructure and damping performance were observed and measured using an optical microscope and a dynamic thermomechanical analysis apparatus (DMA), respectively. The influence of HA and environmental factors (temperature, frequency and strain amplitude) on the damping performance of HA/Mg-3Zn-0.5Zr composites were studied. The results showed that the damping performance of HA/Mg-3Zn-0.5Zr composites increased with increasing HA content and strain amplitude. The damping mechanism was in line with the G-L theory and interface damping theory. The damping values were strongly amplified at 150-300°C. The plot of damping versus temperature showed a peak for the Mg-3Zn-0.5Zr-1HA composite at 235°C. The low frequency damping values of xHA/Mg-3Zn-0.5Zr were higher than the high frequency damping values. It is suggested that the change of damping by a variety of external factors is due to the presence of different dominant damping mechanism at different conditions. Furthermore, it was found that at increased HA content, the grain size of HA/Mg-3Zn-0.5Zr composites decreased and the tensile strength and elongation of HA/Mg-3Zn-0.5Zr composites improved. This work will be beneficial for the study of Mg based joint implant materials with high vibration damping performance.

The Seismic Response Study of Light Steel Storey Adding Structure Considering the Effects of Damping

This paper summarized the current research situation and development direction of the storey adding structure all over the country. On the basis of the situation, combined characteristics of light steel storey adding structure, the article analyzed adding structure's damping distribution regularity. Based on the complex damping theory, through the mode-superposition method, there was established the correction formula of the earthquake response spectrum of light steel storey adding structure considered the effects of damping. All above, the article provides the basis for the study on the dynamic properties of light steel storey adding structure.

Study on Noise Reduction Mechanism and Surface Performance of Crumb Rubber Micro-Surfacing Material

Recently, micro-surfacing is more widely used to protect the asphalt pavement for its superiority in China. This paper investigated the effects of the waste rubber on the micro-surfing material. First, the noise reduction mechanism was analysis. Then, the surface performance of the micro-surfacing mixture was characterized in the laboratory. Sound absorption and vibration damping theory was put forward in this paper. The addition of crumb can slightly improve the surface performance of the pavement.