In order to examine the feasibility of power generation by using friction-induced vibration with a piezoelectric element, we performed experiments and numerical analysis. In the experiments, the generated power in the piezoelectric element and the displacement of an oscillator were measured by a newly developed apparatus that embodied a single-degree-of-freedom (1-DOF) system with friction. In the numerical analysis, an analytical model of a 1-DOF system with friction and piezoelectric element was proposed to simulate the experiments. The experimental results demonstrated that the power of a few microwatts was generated by sliding between a steel ball and a steel plate lubricated with glycerol. In this study, a maximum power of approximately 10 μW was generated at a driving velocity of 40 mm s−1 and a normal load of 15 N. The numerical results demonstrated good qualitative agreement with the experimental results. This implies that this analytical model can be applied to optimize the oscillator design in piezoelectric power generation using friction-induced vibration.

Friction continues to account for the bulk of energy losses in mechanical systems, with an estimated 23% of the world’s total energy consumption used to overcome friction. Concentrated polymer brushes (CPBs) have recently attracted significant scientific and industrial attention, given their ability to achieve superlubricity (i.e., coefficients of friction below 0.01); however, understanding the mechanistic interactions underlying their wear performance has been largely overlooked. Herein, we employ a custom-built optical test apparatus to investigate the inter-dependencies between CPBs and laser-produced surface texture (LST), assessing for the first time the friction, film thickness, and wear behavior in situ and simultaneously. Recent developments in picosecond laser etching allowed us to graft CPBs atop the finest laser-etched matrix of micron-sized dimples reported in literature to date. At low sliding speeds, combined CPB–LST reduces the coefficient of friction to 0.0006, while increasing the CPB durability by up to 34% through a lateral support mechanism offered by the textured micro-features. Furthermore, the imaging results shed light on CPB failure mechanisms. Both these mechanisms of lateral support and failure propagation impact the wear resistance of CPBs and are important in the development of CPBs for future applications (e.g., in low-speed bearings functioning under controlled abrasive wear conditions).

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This paper describes experimental and analytical study on the behavior of falling water sheets. Falling water sheet flowing over a dam sometimes oscillates. It in turn causes vibrations of paper sliding doors or windowpanes of houses in the neighborhood since its frequency is low. Experimental results shows that the frequency of water sheet is the same as that of the pressure in the air chamber. Water sheet vibration is closely related with an air chamber behind the water sheet. The vibration can be suppressed by putting a baffle at an appropriate height in an air chamber. Further, water sheet behavior is analyzed. Comparing experimental data with analytical ones we conclude that sheet vibration occurs around the conditions where the work done by the water sheet on the air chamber reaches a maximum.

Recently, concentrated polymer brushes (CPBs) have attracted much attention as potential tribomaterials showing an ultralow friction coefficient (e.g., 10 À4 in a microtribological analysis). In this study, a homemade apparatus modeling reciprocating seals was developed, which consisted of an inner steel rod and an outer steel ring with a narrow clearance less than several tens of micrometers. A few-micrometer-thick CPB film of poly(methyl methacrylate) well-swollen with an ionic liquid was prepared on each steel surface, and the impact of applying the CPB film to the clearance of reciprocating seals was examined by measuring the leakage rate of a fluid and the friction coefficient in reciprocating motion. The results showed that the CPB film narrowed the clearance between the two steel surfaces, which improved its sealing performance. In addition, the CPB film yielded a quite low friction coefficient (e.g., 10 À3), which assured its smooth motion with small energy loss.