In this work, piezoelectric energy harvesting performance via friction-induced vibration is investigated numerically. A one-degree-of-freedom friction system with a piezoelectric element is proposed, to study the piezoelectric energy harvesting via friction-induced stick-slip vibration. Subsequently, a two-degree-of-freedom friction system with two piezoelectric elements is proposed, to investigate the piezoelectric energy harvesting via model coupling vibration. Results show that regardless of the friction systems, it is feasible to convert friction-induced vibration energy to electrical energy when the friction system is operating in the unstable vibration region. Parametrical analysis indicates that for the one-degree-of-freedom friction system, when the normal load increases from 5 N to 30 N, the stick-slip motion becomes more intense, and the friction system will generate more electric energy. While for the two-degree-of-freedom friction system, with the normal load increase from 20 N to 120 N, there is a critical normal load value for the generation of the strongest vibration and the highest voltage output. When the velocity of the belt increases from 0.5 m/s to 2 m/s, the amplitudes of vibration and output voltage become larger. While with the velocity further increasing, the stick-slip motion and generated electric energy disappear. For both friction systems, the external electric resistance has no effect on the dynamic behaviour of the friction system; however, it can modify the output voltage amplitudes within limits. It is also found that when the force factor of piezoelectric element increases from 3.1 × 10−5 N/V to 3.1 × 10−3 N/V, the vibration and harvested energy gradually increase. When the force factor further increases to 3.1 × 10−2 N/V, the vibration reduces drastically and the corresponding output voltages reduce significantly, which proves that a piezoelectric element with an appropriated force factor can give the highest harvested energy and conversion efficiency.

Rail corrugation refers to the periodic wear of the top working surfaces of rails. This problem has plagued the railway industry over a hundred years. In the present paper, the effects of rail vibration absorbers on wear behaviour of the rail surface have been studied. The dynamic model of a wheel–rail–absorber system is established. The friction contact coupling between the wheel and the rail are fully considered in this model. A wear model, in which the mass loss of unit area in contact patch is proportional to frictional work per unit area between the wheel and the rail, is developed to analyse the wear behaviour of the rail surface. Numerical results show that the saturated creep force-induced self-excited vibration of the wheel–rail system can result in short pitch rail corrugation on the rail surface. The maximum wear depth occurs at the positions close to mid-span of each sleeper bay. After the installation of rail vibration absorbers, the formation of short pitch rail corrugation can be suppressed effectively, and the wear on the rail surface becomes uniform and the growth rate of rail corrugation reduces considerably. Increasing the connection damping between the absorber and the rail web is beneficial to preventing the formation of short pitch rail corrugation.

In this work, piezoelectric energy harvesting (PEH) performance via friction-induced vibration (FIV) is studied numerically. A nonlinear two-degree-of-freedom friction system (mass-on-belt) with piezoelectric elements, which simultaneously considers the stick-slip motion, model coupling instability, separation, and reattachment between the mass and belt, is proposed. Both complex eigenvalue analyses and transient dynamic analysis of this nonlinear system are carried out. Results show that it is feasible to convert FIV energy to electrical energy when the friction system is operating in the unstable vibration region. There exists a critical friction coefficient (μc) for the system to generate FIV and output visible voltage. The friction coefficient plays a significant role in affecting the dynamics and PEH performance of the friction system. The friction system is able to generate stronger vibration and higher voltage in the case that both the kinetic friction coefficient and static friction coefficient are larger than μc. Moreover, it is seen that the separation behavior between contact pair can result in overestimating or underestimating the vibration magnitude and output voltage amplitude, and the overestimate or underestimate phenomenon is determined by the located range of friction coefficient. Furthermore, it is confirmed that an appropriate value of external resistance is beneficial for the friction system to achieve the highest output voltage. The obtained results will be beneficial for the design of PEH device by means of FIV.

The effects of a rail vibration absorber on suppressing short pitch rail corrugation are studied. Firstly, a rail vibration field test is carried out to analyze the vibration response of the rail with and without the vibration absorbers. Secondly, based on the hypothesis that friction-induced self-excited vibration of a wheel-rail system causes rail corrugation; two finite element models of a wheel-rail system and a wheel-rail-absorber system are established and analyzed. Both sets of rail vibration test results and theoretical results show that the rail absorbers can effectively reduce the friction-induced self-excited vibration of the wheel-rail system in the frequency range of 200-800 Hz, which corresponds to frequencies of short pitch rail corrugation. This may be a main reason that the rail vibration absorber can suppress the formation of short pitch rail corrugation.

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