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Prediction of fatigue life is particularly crucial in magnetorheological elastomer (MRE) based rubber components, especially when are exposed to repetitive magnetic and cyclic loading. MREs are smart composites that contain soft elastomer matrix and carbonyl iron particles (CIPs). In this research, silicon rubber was mixed with 20% of CIPs in the absence of an external magnetic field to produce MREs. Firstly, for the determination of material constants (including hyper elastic, magnetic, and viscoelastic), two types of tests such as uniaxial compression and relaxation, were performed on the samples. Then, fatigue tests were performed by a servo-hydraulic fatigue testing machine with cyclic loading in a repetitive magnetic field. Fatigue equations were obtained based on the number of fatigue life and maximum stress. The results confirmed that maximum stress could be used as a trustworthy fatigue life predictor for MREs when they are subjected to a combination of repetitive magnetic and cyclic loading. Scanning electron microscopy images from fatigue crack showed that the internal structure of MREs became stronger in the direction of the magnetic field. The maximum stress of the MRE was smaller in the absence of a magnetic field and decreased as the number of fatigue cycles increased with and without the magnetic field. [ABSTRACT FROM AUTHOR]

The application of piezoelectric materials in energy harvesting devices has become an interesting topic for designers in recent years. Most of the reported works consider electrical power as a major parameter throughout the design procedure. What is less discussed is considering other design factors like the fatigue life of the harvester as well as the financial costs of the device. In this research, a methodology is introduced to design an optimum harvester, taking into account the aforementioned design factors. The finite element model of a piezoelectric harvester used in roadways is developed and validated. The fatigue test constants of the piezoelectric material are extracted via a novel approach. A parametric study is conducted on the model to generate a dataset containing electrical and mechanical characteristics, where it is used as an input for training an artificial neural network to model the behavior of the harvester. In order to evaluate the level of importance of the optimization objectives, two methods are employed: the Shannon entropy method and equal weighting factors. Results show the effectiveness of the model, where considering the electromechanical characteristics of the module is important in terms of overall performance, efficiency, durability, and financial costs. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting is an efficient technique among energy scavenging methods employed in asphalt pavements. Several designs are reported in the literature; however, what is less discussed is how to design the harvester. In this paper, a fixed volume of piezoelectric material is considered, and various design parameters are discussed in order to achieve an improved design. The main objective is to enhance the harvester performance, considering electrical and mechanical aspects, simultaneously. The output power, the level of induced stress on the piezoelectric material, the endurance limit, and the coupling effect of the device with the pavement are considered. As a case study, the finite element model of a piezoelectric harvester is developed and validated with the experimental results. A parametric study is then carried out in order to improve both the electrical and mechanical characteristics of the device. Various parameters, such as piezoelectric disks cross-section, piezoelectric material, as well as the disks aspect ratio are considered. The proposed structures are compared with similar ones reported in the literature and show higher output powers of 3 − 5.8 times. A case study is presented to show the signal conditioning process of the harvested power for practical applications. Improvements in various aspects of the device performance, while considering the economic aspects, i.e., the amount of consumed piezoelectric material, show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In this article, free vibration behavior of a rotating nano/microcircular plate constructed from functionally graded magneto-elastic material is simulated with the first-order shear deformation theory. For the sake of comparison, the nonlocal elasticity theory and the modified couple stress theory are employed to implement the small size effect in the natural frequencies behavior of the nano/microcircular plate. The governing equations of motion for functionally graded magneto-elastic material nano/microcircular plates are derived based on Hamilton's principle; comparing the obtained results with those in the literature, they are in a good agreement. Finally, the governing equations are solved using the differential quadrature method. It is shown that the vibrational characteristics of functionally graded magneto-elastic material nano/microcircular plates are significantly affected by non-dimensional angular velocity, size dependency of the Eringen's and the modified couple stress theories, and power law index for clamped and hinged boundary conditions. Results show that a critical point occurs by increasing the angular velocity and the effect of several parameters are changed after this point. [ABSTRACT FROM AUTHOR]

This article investigates free vibration of a functionally graded piezomagnetic material cylindrical nanoshell embedded in viscoelastic media under rotational, external electric and magnetic loadings. The governing equations of the nanoshell are derived based on Eringen's nonlocal theory. It is found that, magnetic and piezoelectric properties of the structure change exponentially along the thickness. The rotational loading is calculated considering initial hoop tension. The results are obtained by applying generalized differential quadrature method to the governing equations and associated boundary conditions. Results also include those achieved for clamped-clamped and simply hinged-hinged boundary conditions. It is found that free vibration characteristics of functionally graded piezomagnetic material cylindrical nanoshell are influenced by several factors including angular velocity, length scale parameter, external voltage, external amperage, functionally graded power index, and viscoelastic media parameters. [ABSTRACT FROM AUTHOR]