Ahmet Yapici

Design and testing of an efficient and compact piezoelectric energy harvester

Piezoelectric materials generate electricity when they are subjected to dynamic strain. In this paper compact size self contained energy harvesters were built by considering typical space available for AA size batteries. Each of the harvesters contains a rectifier circuit with four diodes and a capacitor. A series of piezoelectric energy harvesters with circular and square cross-sections were built and tested at different frequency and amplitude levels. On 1M? impedance digital oscilloscope, it was observed that the voltages reached to 16V (round cross-section) and 25V (square cross-section) at 50Hz frequency. The highest power output accomplished was 625µW. The outputs of both types of the harvesters were very similar at low amplitudes. However, the square cross-section facilitates better attachment of the piezoelectric elements with the harvester shell and worked efficiently at higher amplitudes without immediate failure.

Elastic-Plastic Stress Analysis of Woven Cr-Ni-reinforced Composite-laminated Plates with a Hole under In-plane Loading

An elastic-plastic stress analysis and the expansion of plastic zone in layers of woven steel fiber-reinforced thermoplastic matrix-laminated plates are studied by using the Finite Element Method and the First-order shear deformation theory for small deformations. Composite structures consisting of woven Cr-Ni wire as a fiber and F2.12 low-density polyethylene as a thermoplastic matrix were manufactured by hot-press molding. The mechanical properties were experimentally determined. The effect of orientation angle and symmetric-antisymmetric structures were investigated. It is assumed that the laminated plates are subjected to in-plane uniform loads. Loading is gradually increased from yield point of the plate as 0.01 MPa at each load step. Load steps are chosen as 300, 400, and 500.

Development of Piezoelectric Strain Gages for Structural Health Monitoring Applications

The strain monitoring capability of piezoelectric materials was experimentally studied. Patches and fibers were considered for this purpose. A piezoelectric stripe actuator was used to obtain the typical signal of patches. Two designs were considered for the piezoelectric fibers. The first one was a commercial energy harvesting device with long fibers. The ends of the fibers were loose. In contrast, we designed a small piezoelectric strain gage with short fibers. Fibers were attached to wires at two ends with conductive resin. The piezoelectric strip actuator, and commercial energy harvesting device were connected to digital oscilloscope directly. A charge amplifier was used to condition the signals of the small piezoelectric strain gage with short fibers. All the units were attached to a beam and excited at different frequencies to evaluate the characteristics of their signals.

The Effect of Nylon 6.6 Nanofiber Layers on Mechanical Properties of Epoxy

1 Mechanical Engineering Department, Iskenderun Technical University, Iskenderun 31200, Turkey 2 Seydisehir Vocational School, Necmettin Erbakan University, Konya 42370, Turkey 3 Ilgın Vocational School, Selcuk University, Konya, 42600, Turkey --------------------------------------------------------ABSTRACT----------------------------------------------------------In this study mechanical properties of epoxy resin reinforced with different numbers of nanofiber layers of nylon 6.6 which produced with electrospinning method was investigated. Solution of 10 wt % of Nylon 6.6/ formic acid was used for electrospinning. The special molds were prepared to produce the laminated composite plates. Static tensile tests were performed, and the specimens were evaluated with respect to tensile strength and elongation at break, which are aspects of their basic mechanical properties.

Study of the Computational Efficiency and Validity of the Surface Response to Excitation Method.

Performance of the Surface Response to Excitation (SuRE) method was evaluated by using a low cost DSP system and spectrum analyzer. SuRE method excites the surface of the structure with a piezoelectric element. The generated vibrations of a critical point on the surface are measured with (a) piezoelectric element(s) or other sensor(s). The magnitude of the transfer function between the excitation and the sensory signal is monitored. The accuracies of the Teager-Kaiser (TKA), Goertzel, RMS and average of the positive values algorithms were evaluated for magnitude estimation. The SuRE method was used successfully for detection of the compression by using the DSP system. In addition, an applied compressive force, a change of the diameter of a hole and a composite coating was detected by using a spectrum analyzer. The study indicated that the SuRE may be used as a low cost alternative to impedance method. The cost and inconvenience of using multiple piezoelectric elements are the disadvantageous of the method. The main advantages of the SuRE are requirement of much cheaper and simpler equipment. Test time may be drastically shortened in low noise environments, many different transducers may be used for sensing and some directionality may be gained by carefully selecting the location of the sensor(s).

Contact Problem for a Transversely Isotropic Cylinder Radially Compressed by a Rigid Toroidal Indenter

In this study, an elastostatic contact problem for a radially compressed transversely isotropic cylinder subjected to radial compression through a circumferential indenter is considered. The extent of the contact region and the stress distribution are sought. The problem is formulated for an elastic cylinder in the absence of body forces. It is assumed that the contact between the cylinder and the rigid indenter is frictionless and only compressive normal tractions can be transmitted through the interface. Due to the geometry of the configuration, Fourier transform techniques are chosen. The problem is reduced to a singular integral equation. It is reduced to linear algebraic equations system by using Gauss Chebyshev Integration Formulae. This system is solved by using the Gauss Elimination method. The values are evaluated for various discrete points. Numerical results for the radial stress and the distance characterizing the contact area are given in graphical form for single circular smooth indenter.