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Since 2012 there has been a rapid rise in the development of triboelectric nanogenerators due to their potential applications in the field of energy harvesting and self-powered sensors for vibrations, accelerations, touches, pressures and other mechanical motions. This study suggests a novel triboelectric nanogenerator based on the interaction between polyvinylidene fluoride and polyvinylpyrrolidone submicron fibers. Polyvinylpyrrolidone is introduced as a new material for the TENG because of its tendency of losing electrons easily, while polyvinylidene fluoride is selected for its strongelectron attracting ability. Electrospinning is suggested as a fabrication method for the nanofibers due to its simplicity, versatility and low-cost. Furthermore, the paper explores the possibility to use this triboelectric nanogenerator as a self-powered pressure sensor. For this purpose, the nanogenerator is subjected to dynamic mechanic analysis which produces controlled pressure forces applied with a certain frequency. This is the first work to suggest the use of dynamic mechanical analyzer to study the relation between the applied mechanical stimulus and the electric responses of the triboelectric nanogenerator. Eventually the sensitivity of the nanogenerator to different pressures is analysed. A directly proportional relationship is found between the pressure applied and the resultant voltage and current amplitudes. The developed nanogenerator reacts to pressure in real time and as a sensor it exhibits a very high sensitivity and low experimental error for repeated measurements. The main contributions of this study are the development of a novel nanogenerator based on the triboelectric effect between polyvinylidene fluoride and polyvinylpyrrolidone electrospun fibers and the investigation for its potential use as a selfpower pressure sensor. Eventually, the paper explores the advantages of dynamic mechanical analyzer for pressure analysis.

This study proposes an analytical model for vibrations in a cracked rectangular plate as one of the results from a program of research on vibration based damage detection in aircraft panel structures. This particular work considers an isotropic plate, typically made of aluminum, and containing a crack in the form of a continuous line with its center located at the center of the plate and parallel to one edge of the plate. The plate is subjected to a point load on its surface for three different possible boundary conditions, and one examined in detail. Galerkin’s method is applied to reformulate the governing equation of the cracked plate into time dependent modal coordinates. Nonlinearity is introduced by appropriate formulations introduced by applying Berger’s method. An approximate solution technique—the method of multiple scales—is applied to solve the nonlinear equation of the cracked plate. The results are presented in terms of natural frequency versus crack length and plate thickness, and the nonlinear amplitude response of the plate is calculated for one set of boundary conditions and three different load locations, over a practical range of external excitation frequencies.

In this article, the effect of polycaprolactone nanofibers on the dynamic behavior of glass fiber reinforced polymer composites is investigated. The vibratory behavior of composite beams in their pristine state (without any nano modification) and the same beams modified with polycaprolactone fibers is considered experimentally. The experimental results show that the incorporation of polycaprolactone nanofibers increases the damping; however, it does not significantly affect the natural frequencies. Additionally, the paper analyses the effect of polycaprolactone nanofibers on the impact behavior of glass fiber/epoxy composites. This has already been analyzed experimentally in a previous study. In this work, we developed a finite element model to simulate the impact behavior of such composite laminates. Our results confirm the conclusions done experimentally and prove that composites reinforced with polycaprolactone nanofibers are more resistant to damage and experience less damage when subjected to the same impact as the pristine composites. This study contributes to the knowledge about the dynamic behavior and the impact resistance of glass fiber reinforced polymer composites reinforced with polycaprolactone nanofibers. The findings of this study show that interleaving with polycaprolactone nanofibers can be used to control the vibrations and improve the impact damage resistance of structures made of composite mats as aircrafts or wind turbines.

This study proposes a methodology for rolling element bearings fault diagnosis which gives a complete and highly accurate identification of the faults present. It has two main stages: signals pretreatment, which is based on several signal analysis procedures, and diagnosis, which uses a pattern-recognition process. The first stage is principally based on linear time invariant autoregressive modelling. One of the main contributions of this investigation is the development of a pretreatment signal analysis procedure which subjects the signal to noise cleaning by singular spectrum analysis and then stationarisation by differencing. So the signal is transformed to bring it close to a stationary one, rather than complicating the model to bring it closer to the signal. This type of pre-treatment allows the use of a linear time invariant auto-regressive model and improves its performance when the original signals are non-stationary. This contribution is at the heart of the proposed method, and the high accuracy of the diagnosis is a result of this procedure. The methodology emphasizes the importance of preliminary noise cleaning and stationarisation. And it demonstrates that the information needed for fault identification is contained in the stationary part of the measured signal. The methodology is further validated using three different experimental setups, demonstrating very high accuracy for all of the applications. It is able to correctly classify nearly 100 percent of the faults with regard to their type and size. This high accuracy is the other important contribution of this methodology. Thus, this research suggests a highly accurate methodology for rolling element bearing fault diagnosis which is based on relatively simple procedures. This is also an advantage, as the simplicity of the individual processes ensures easy application and the possibility for automation of the entire process