Stress calculation method of bending multilayer structural element when bending moment acts in the planes that do not coincident with principal planes

This paper presents stress calculationmethod of bending multilayer structural element when bending moment acts in the planes that do not coincident with principal planes, and cross section is symmetric or asymmetric. Carrying the computation of occurring stress values in multilayer beam layers it is necessary to identify coordinates of cross-section stiffness centre, direction of principal axes, and coordinates of specific points regarding principal axes. Having this information and equation which is valid for stress calculation of bending multilayer beams it is possible to identify normal stress values at any point of the beam cross section under skew bending. It is deduced that stress values and the nature of their changes are influenced by the shape of beam cross-section, its asymmetry degree, and the direction of appliedmoment.

Electromechanical Modeling of a Piezoelectric Vibration Energy Harvesting Microdevice Based on Multilayer Resonator for Air Conditioning Vents at Office Buildings

Piezoelectric vibration energy harvesting (pVEH) microdevices can convert the mechanical vibrations to electrical voltages. In the future, these microdevices can provide an alternative to replace the electrochemical batteries, which cause contamination due to their toxic materials. We present the electromechanical modeling of a pVEH microdevice with a novel resonant structure for air conditioning vents at office buildings. This electromechanical modeling includes different multilayers and cross-sections of the microdevice resonator as well as the air damping. This microdevice uses a flexible substrate and it does not include toxics materials. The microdevice has a resonant structure formed by multilayer beams and U-shape proof mass of UV-resin (730 μm thickness). The multilayer beams contain flexible substrates (160 μm thickness) of polyethylene terephthalate (PET), two aluminum electrodes (100 nm thickness), and a ZnO layer (2 μm thickness). An analytical model is developed to predict the first bending resonant frequency and deflections of the microdevice. This model considers the Rayleigh and Macaulay methods, and the Euler-Bernoulli beam theory. In addition, the electromechanical behavior of the microdevice is determined through the finite element method (FEM) models. In these FEM models, the output power of the microdevice is obtained using different sinusoidal accelerations. The microdevice has a resonant frequency of 60.3 Hz, a maximum deflection of 2.485 mm considering an acceleration of 1.5 m/s2, an output voltage of 2.854 V and generated power of 37.45 μW with a load resistance of 217.5 kΩ. An array of pVEH microdevices connected in series could be used to convert the displacements of air conditioning vents at office buildings into voltages for electronic devices and sensors.

Non Destructive Testing of Low Profile Light Weight Track System

The paper presents the results of the responses of a concrete trough of a new lightweight rail track system (LR55) to full scale non destructive tasting. The system which is made from three main components; low profile steel rail, elastomeric pad and prestressed concrete trough is developed for light rail transits in cities streets, which can significantly help in improving the traffic flow, reducing the traffic congestion and thus providing opportunities for minimising serious environmental problems such as level of noise, vibration and air pollutions and in this regards it can be considered as environmentally friendly means of transport. A mathematical model was developed where the LR55 track system was treated as multilayer beams on elastic foundations, and the model was then validate experimentally through a series of non-destructive tests on full scale model subjected to a full scale service load specified by the current BS codes of practises.