Electro-mechanical analysis of a multilayer piezoelectric cantilever energy harvester upon harmonic vibrations

This paper addresses an important issue of the individual layer thickness influence in a multilayer piezo composite on electro-mechanical energy conversion. The use of energy harvesting systems seems to be very promising for applications such as ultra-low power electronics, sensors and wireless communication. The energy converters are often disabled due to a failure of the piezo layer caused by an excessive deformation/stresses occurring upon the operation. It is thus desirable to increase both reliability and efficiency of the electromechanical conversion as compared to standard concepts. The proposed model of the piezoelectric vibration energy harvester is based on a multilayer beam design with active piezo and protective ceramic layers. This paper presents results of a comparative study of an analytical and numerical approach used for the electro-mechanical simulations of the multilayer energy harvesting systems. Development of the functional analytical model is crucial for the further optimization of new (smart material based) energy harvesting systems, since it provides much faster response than the numerical model

Experimentally Verified Analytical Models of Piezoelectric Cantilevers in Different Design Configurations

This paper deals with analytical modelling of piezoelectric energy harvesting systems for generating useful electricity from ambient vibrations and comparing the usefulness of materials commonly used in designing such harvesters for energy harvesting applications. The kinetic energy harvesters have the potential to be used as an autonomous source of energy for wireless applications. Here in this paper, the considered energy harvesting device is designed as a piezoelectric cantilever beam with different piezoelectric materials in both bimorph and unimorph configurations. For both these configurations a single degree-of-freedom model of a kinematically excited cantilever with a full and partial electrode length respecting the dimensions of added tip mass is derived. The analytical model is based on Euler-Bernoulli beam theory and its output is successfully verified with available experimental results of piezoelectric energy harvesters in three different configurations. The electrical output of the derived model for the three different materials (PZT-5A, PZZN-PLZT and PVDF) and design configurations is in accordance with lab measurements which are presented in the paper. Therefore, this model can be used for predicting the amount of harvested power in a particular vibratory environment. Finally, the derived analytical model was used to compare the energy harvesting effectiveness of the three considered materials for both simple harmonic excitation and random vibrations of the corresponding harvesters. The comparison revealed that both PZT-5A and PZZN-PLZT are an excellent choice for energy harvesting purposes thanks to high electrical power output, whereas PVDF should be used only for sensing applications due to low harvested electrical power output

Computational modelling of the layered piezoelectric composites and analysis of their electro-mechanical response upon harmonic vibrations

V současnosti je velmi aktuálním tématem generování elektrické energie z alternativních zdrojů, zejména z vibrací. Zařízení, která přeměňují mechanickou energii na elektrickou, využívají často ke své činnosti piezoelektrický jev. Pro optimální nastavení takového elektromechanického měniče pro danou aplikaci je třeba mít k dispozici výpočtový model, který bude schopný postihnout všechny klíčové aspekty jeho provozu. Tato práce se tedy zabývá vytvořením takovéhoto nástroje, který je schopen komplexně popsat elektromechanickou odezvu studovaného piezoelektrického měniče energie v podobě vetknutého, vícevrstvého keramického nosníku s piezoelektrickými vrstvami. Uvažovaná vícevrstvá konstrukce je během své činnosti vystavena kinematickému buzení a je rovněž zatížena tepelnou zbytkovou napjatostí vznikající při její výrobě. Vytvořený výpočtový model využívá klasickou laminátovou teorii k určení statické elektromechanické odezvy dané konstrukce. Elektromechanická odezva při kmitání uvažované konstrukce v ustáleném stavu je získána s využitím Hamiltonova variačního principu a teorie kmitání prutů. Vytvořený výpočtový model je dále schopen odhadnout zdánlivou lomovou houževnatost dané vícevrstvé konstrukce pomocí metody váhových funkcí. Výstupy vytvořeného výpočtového modelu jsou ověřeny s využitím numerických simulací na bázi MKP a dostupných experimentálních výsledků. V diplomové práci je následně vytvořený výpočtový model aplikován při hledání optimálního rozložení jednotlivých vrstev konkrétního vícevrstvého nosníku s cílem maximalizovat jeho elektrický výkon a odolnost vůči šíření povrchových trhlin, resp. vzniku křehkého lomu. Tohoto cíle je dosaženo pomocí vhodného rozložení tepelných zbytkových napětí v jednotlivých vrstvách uvažované konstrukce (řízeného použitými materiály a tloušťkami jednotlivých vrstev).Currently, a generation of electric power from alternative sources of energy, especially from ambient vibrations, is becoming a very hot topic. Devices converting mechanical energy into an electrical one are called energy harvesters and are often based on the piezoelectric phenomenon. For the optimal adjustment of such an energy converter in the given application, it is necessary to have its computational model, which is able to describe all key aspects of its operation. Thus, this work focuses on the development of such a complex computational tool, which is able to globally describe the electromechanical response of the studied piezoelectric harvester operating in the form of a cantilever multilayer ceramic beam with piezoelectric layers. Such a multilayer structure is subjected to a kinematic excitation during its operation and also contains thermal residual stresses coming from the manufacturing process. The derived computational model utilizes the classical laminate theory to determine the static electromechanical response of the structure. Hamilton’s variational principle and the theory of beam vibrations were employed to obtain electromechanical response of the structure upon steady-state vibrations. The complex computational model is also capable of estimating the apparent fracture toughness of a given multilayer structure using the weight function method. The output of derived computational model is validated with FE simulations and available experimental results. This master’s thesis also presents an application of the derived computational model in the optimization of a particular multilayer beam to obtain maximal electrical power output and to maximize its resistance to surface crack propagation and a potential brittle fracture. This goal is achieved by means of a suitable adjustment of thermal residual stresses in particular layers of the considered structure (controlled by used materials and by thicknesses of particular layers).

Modelling and analysis of the contact failure of ceramic materials

This bachelor thesis deals with contact damage of ceramic materials. The purpose of this work is to create an analytical and FEM model of contact between a sphere and flat plate and subsequently use these models to analyse loading conditions that lead to crack initiation in the ceramic plate. The research part contains description of contact failures in ceramic materials with strong emphasis on Hertzian cone crack, followed by Hertzian theory of contact between two spheres and Hertzian stress field equations for flat plate. The next part of research chapters describes how contact problems are modelled in FEM software ANSYS Mechanical APDL and introduces the basics of fracture mechanics, which are necessary for the prediction of ring crack initiation. The next chapter contains information about the creation of analytical and FEM model and includes illustrative results of both models, which are then compared between these two models. The last chapter of this work deals with fracture mechanics FEM model that can simulate the ring crack initiation. This chapter also contains analysis of ideal crack position, where the crack has the best conditions for its initiation and growth. The last part of this chapter contains parametrical study where critical loading conditions are analysed in relation to radius of indentation sphere and different mechanical properties of used ceramic plate. In the final part of this work, the results of fracture mechanics FEM model are compared to experimental results of real specimens

Analysis of piezoelectric skin on vibrating structure for energy harvesting and structural health monitoring applications

The paper deals with a computational and experimental analysis of the relation between the layout of PVDF (polyvinylidene fluoride) patches on the vibrating structure and generated mean electrical power/voltage on them at different vibrational conditions (excited mode shapes). The electromechanical response of (variously distributed) PVDF patches upon vibrations of the plate is analysed in details using the FE model and a harmonic analysis. In the next step the simulation outputs are confronted and verified with experimental observations made on the real vibrating plate. Results of the numerical modelling define the most suitable and effective distribution of patches on the vibrating structure and an optimal connected resistance in their circuit, leading to a highest generated electrical power/voltage upon vibrations at various mode shapes. A comparison of simulation outputs with performed experiments shows a good agreement between both approaches which makes the modelling an applicable approach for a design of effective piezoelectric skins on (large) vibrating structures for both the energy harvesting and structural health monitoring application