Search

Commercial high-speed train friction blocks with a hole in the middle of the surface and perforated blocks filled with additive materials are introduced in drag brake experiments conducted on a customized small-scaled braking dynamometer. These additive materials include Cu-based powder metallurgy material, composite material, and a Mn–Cu damping alloy. The results indicate that the filling materials significantly influence the wear behavior of a braking interface and the characteristics of friction-induced vibration. Under the same experimental conditions, the perforated blocks filled with different materials produce different types of wear debris and exhibit different wear evolutions, markedly changing the wear debris distribution and surface morphology. These changes lead to variations in thermal distribution on the surfaces of both the friction block and brake disc. The study also shows that as a filling material, the Mn–Cu damping alloy can suppress the friction-induced vibration of the brake system, resulting in the lowest level of brake noise among all brake systems. However, the original friction block (i.e., the block without any filling material) can trap wear debris because of its perforated structure. The structure produces less friction-induced vibration and noise, compared with the block filled with powder metallurgy material. The noise performance of the composite material block is superior to the noise performance of the block without any filling material (i.e., the original block) and the block with powder metallurgy material but inferior to that of the block filled with the Mn–Cu damping alloy. Finite element analysis indicates that the properties of the filling materials exert no effect on the unstable vibration intensity of the brake system. Therefore, the wear debris behavior of the filling materials and the interface wear characteristics influence the friction-induced vibration and noise of the brake system.

In this study, to investigate the effect of the hexagon friction block installation direction on the surface tribology and friction-induced vibration and noise (FIVN), tribological tests were carried out on a self-manufactured high-speed train brake dynamometer under different installation directions. Accordingly, a finite element (FE) model with material parameters and boundary conditions coinciding with the test rig was used to conduct complex eigenvalue analysis (CEA), and the Archard wear formula was employed to simultaneously study the wear and vibration. The results demonstrate that the installation direction has little effect on the frequency and mode shape of unstable modes, but the FIVN intensity, the phase-space characteristics of the friction noise, and the damping ratio of the brake system are changed. The contact stress and wear are found to be mainly distributed in the leading edge and the inner area of the friction block, leading to the severe eccentric wear phenomenon, and the friction heat is mainly concentrated in this area and the inner region of the disc friction area. The degree of uneven wear of the block is found to vary with the change of its installation direction, which also causes differences in the amount of wear debris flowing in the brake interface and the damage to the interface. Under the joint action of wear debris, friction heat, and contact stress, the brake interfaces of the brake systems with different block installation directions are found to exhibit different tribological behaviors, which affects the intensity of FIVN and the phase-space characteristics of friction noise. Therefore, it is necessary to consider the influence of the block installation direction on the tribological and dynamic behaviors of the brake interface of high-speed trains when designing the brake pad, which can aid in the development of a brake pad with excellent interface tribological behavior and friendly FIVN characteristics.

Vibration reduction and energy harvesting were achieved by installing a piezoelectric cantilever beam (PZT-beam). Experimental work was carried out on a self-developed tribology and dynamic behavior simulation test device. Finite element (FE) model and numerical simulation model were established to analyze the effect of the PZT-beam on the dynamical response, system stability and the vibration energy harvesting performance of the brake system. The experimental and simulation results show that friction-induced vibration (FIV) can be reduced via a PZT-beam, and the vibration energy can be converted into electrical energy through the deformation of the PZT-beam. The PZT-beam can significantly reduce the real part of the complex eigenvalues of the brake system without significantly changing the unstable vibration frequency and mode shape.

In this work, the effect of a time-varying contact surface on friction-induced vibration and noise (FIVN) and surface wear performance was studied experimentally. A certain size groove was fabricated on a surface of compacted graphite iron, then filled with pure phenolic resin and phenolic resin with MoS2 additives to obtain a surface with time-varying contact characteristics. The experiment was carried out in a ball-on-flat configuration. The results show that introducing the filler of phenolic resin with MoS2 additives into the groove is effective not only at suppressing the generation of FIVN and improving surface wear performance, but also at alleviating the impact vibration between the groove edge and the ball. More importantly, the time-varying contact surfaces designed in this work are valuable for exploring the role played by debris in the modification of wear state and the formation of interfacial characteristics, and how this finally affects the generation of FIVN. The investigation shows that a time-varying contact surface filled with suitable materials can realize the aim of FIVN reduction.

Drag brake experiments using hexagonal, pentagonal, and circular friction blocks are conducted using a self-designed small-scale brake dynamometer to investigate the influence of the friction block shape on the tribological and dynamical behaviours of high-speed train brakes. A four-degree-of-freedom model that considers the interface contact behaviour is established to investigate the influence of the contact stiffness at the friction interface on the stability and vibration characteristics of the braking system. The experimental results show that the surface of the hexagonal friction block is slightly worn, and the contact plateaus is relatively uniform in size, whereas the pentagonal and circular friction blocks show visible ploughing and exfoliation and a significant proportion of large contact plateaus. Accordingly, the hexagonal friction block produces considerably less friction-induced vibration and noise than the pentagonal block and the circular block. Moreover, analysis of the vibration characteristics of the friction system indicates that the interface of the hexagonal friction block is mainly subjected to normal impact, whereas the interfaces of the other two blocks exhibit significantly more ploughing and shearing action in the tangential direction. In general, higher contact stiffness results in stronger friction-induced vibration, thereby enhancing the instability of the friction system. In this work, it is found that the friction block shape has a significant effect on the contact pressure distribution. The hexagonal friction block exhibits a more uniform distribution of contact pressure than the pentagonal and circular friction blocks, resulting in the lowest contact stiffness, as well as the least wear, vibration, and noise.

Tribological tests and wear simulation were conducted to study the influence of the installation of cantilever beams on the tribological behavior of the brake interface. The results show that the worn surface of the original brake system exhibited complex tribological behavior. After installing the cantilever beams, the eccentric wear of the worn surface was found to be significantly reduced and the temperature distribution of the disc surface was more uniform. The vibration of the cantilever beams was found to propagate to the brake interface, resulting in relatively uniform contact. As a result, the tribological behavior of the braking interface was improved, and this improvement was enhanced when the cantilever beams were installed in both the normal and tangential directions.

The effects of the macroscopic surface morphology caused by the uneven wear on friction induced vibration were investigated. The experimental results showed the uneven wear in the sliding direction produced the contact plateaus with large theoretical contact lengths at the leading edge and increased the unstable vibrations. A numerical analysis of the contact pressure distribution in different macroscopic surface morphology indicated variation of contact pressure deteriorated the wear status, thus increased the tendency of unstable vibration. And the stability of the friction system decreased with the changes in the macroscopic surface morphology. The lumped parameter model proved the uneven wear in the sliding direction would decrease the stability of the system and increase the coupling of tangential and normal vibration.

In this work, the effect of friction block configuration on the brake squeal of a high-speed train is investigated. Three friction block configurations of simplified brake pads are used in the brake tests. The test results indicate that friction block configuration has a significant effect on the noise performance of the brake system. Finite element analysis reveals that the break squeal occurs due to the mode coupling of the brake system. Different friction block configurations lead to different mode characteristics, contact behaviors, and noise performances. Moreover, a full-scale finite element model of the high-speed train brake system is established. The simulation results show that the friction block configuration with a relatively even distribution of the interfacial contact pressure has a relatively lower squeal propensity. Therefore, adjustment of the friction block configuration is an efficient method for noise reduction of railway brakes.

In this study a method for simultaneous energy harvesting via friction-induced vibration and vibration reduction is proposed and implemented by sandwiching a piezoelectric patch between two layers of elastic damping components. A test bench that provides good repeatability and generates friction-induced vibration is developed. The experimental results show that the elastic damping components significantly suppress friction-induced vibration. The fluctuating voltage signals indicated the feasibility of the proposed approach for energy harvesting via friction-induced vibration. Several parallel grooves are fabricated on the surface of the elastic damping components to investigate the influence of damping components with different structures on the vibration reduction and energy recovery performance. The results show that the grooved damping components provide a greater reduction in the vibration level of the system than the smooth damping components, but the voltage signals are also weaker. Numerical analysis are performed in ABAQUS 6.14. The unstable mode shape shows that the elastic damping components and piezoelectric patch produce relatively large deformation, demonstrating the feasibility of the proposed energy harvesting approach. The results obtained from the implicit dynamic analysis are identical to the experimental results. Therefore, the implicit dynamic analysis is used to provide some reasonable explanations for the experimental phenomena.