Vladimir Z. Parton

Bio: Vladimir Z. Parton is an academic researcher. The author has contributed to research in topics: Fracture (geology) & Fracture mechanics. The author has an hindex of 1, co-authored 1 publications receiving 475 citations.

Fracture mechanics for piezoelectric ceramics

Abstract: We Study cracks either in piezoelectrics, or on interfaces between piezoelectrics and other materials such as metal electrodes or polymer matrices. The projected applications include ferroelectric actuators operating statically or cyclically, over the major portion of the samples, in the linear regime of the constitutive curve, but the elevated field around defects causes the materials to undergo hysteresis locally. The fracture mechanics viewpoint is adopted—that is, except for a region localized at the crack tip, the materials are taken to be linearly piezoelectric. The problem thus breaks into two subproblems: (i) determining the macroscopic field regarding the crack tip as a physically structureless point, and (ii) considering the hysteresis and other irreversible processes near the crack tip at a relevant microscopic level. The first Subproblem, which prompts a phenomenological fracture theory, receives a thorough investigation in this paper. Griffith's energy accounting is extended to include energy change due to both deformation and polarization. Four modes of square root singularities are identified at the tip of a crack in a homogeneous piezoelectric. A new type of singularity is discovered around interface crack tips. Specifically, the singularities in general form two pairs: r1/2±ieand r1/2±ie, where e. and k are real numbers depending on the constitutive constants. Also solved is a class of boundary value problems involving many cracks on the interface between half-spaces. Fracture mechanics are established for ferroelectric ceramics under smallscale hysteresis conditions, which facilitates the experimental study of fracture resistance and fatigue crack growth under combined mechanical and electrical loading. Both poled and unpoled fcrroelectrie ceramics are discussed.

Electrostatic potential in a bent piezoelectric nanowire. The fundamental theory of nanogenerator and nanopiezotronics

Abstract: We have applied the perturbation theory for calculating the piezoelectric potential distribution in a nanowire (NW) as pushed by a lateral force at the tip. The analytical solution given under the first-order approximation produces a result that is within 6% from the full numerically calculated result using the finite element method. The calculation shows that the piezoelectric potential in the NW almost does not depend on the z-coordinate along the NW unless very close to the two ends, meaning that the NW can be approximately taken as a “parallel plated capacitor”. This is entirely consistent to the model established for nanopiezotronics, in which the potential drop across the nanowire serves as the gate voltage for the piezoelectric field effect transistor. The maximum potential at the surface of the NW is directly proportional to the lateral displacement of the NW and inversely proportional to the cube of its length-to-diameter aspect ratio. The magnitude of piezoelectric potential for a NW of diameter 50 nm and length 600 nm is 0.3 V. This voltage is much larger than the thermal voltage (25 mV) and is high enough to drive the metal-semiconductor Schottky diode at the interface between atomic force microscope tip and the ZnO NW, as assumed in our original mechanism for the nanogenerators. Developing novel technologies for wireless nanodevices and nanosystems is of critical importance for applications in biomedical sensing, environmental monitoring, and even personal electronics. Miniaturization of a power package and self-powering of these tiny devices are some key challenges for their applications. Various approaches have been developed for harvesting energy from the environment based on approaches such as thermoelectricity and piezoelectricity. Innovative nanotechnologies are being developed for converting mechanical energy (such as body movement, muscle stretching), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as body fluid and blood flow) into electric energy that will be used to power nanodevices that operate at low power. Recently, using piezoelectric ZnO nanowire (NW) arrays, a novel approach has been demonstrated for converting nanoscale mechanical energy into electric energy. 1-3 The single nanowire nanogenerator (NG) relies on the bending of a NW by a conductive atomic force microscope (AFM) tip, which transfers the displacement energy from the tip to the elastic bending energy of the NW. The coupled piezoelectric and semiconducting properties of the NW perform a charge creation, accumulation, and discharge process. Most recently, this approach has been extensively developed to produce continuous direct-current output with the use of aligned NWs that were covered by a zigzag top electrode, and the nanogenerator was driven by ultrasonic wave, establishing the platform of producing usable power output for nanodevices by harvesting energy from the environment. 4 Furthermore, based on the coupled piezoelectric and semiconducting properties of the NW, a new field of nanopiezotronics has been created, 5,6 which is the basis for fabricating piezoelectric field effect transistors, 7 piezoelectric diode, 8 piezoelectric force/humidity/chemical sensors, 9 and more. The theoretical background for the nanogenerator and nanopiezotronics is based on a voltage drop created across the cross section of the NW when it is laterally deflected, with the tensile side surface in positive voltage and compressive side in negative voltage. 1,5 It is essential to quantitatively calculate and even develop analytical equations that can give a direct calculation of the voltage at the two side surfaces of the NW, which is important to calculating the efficiency of the nanogenerator and the operation voltage of the nanopiezotronics. In the literature, numerous theories for onedimensional (1D) nanostructure piezoelectricity have been proposed, including first-principles calculations, 10,11 molecular dynamics (MD) simulations, 12 and continuum models. 13

Linear electro-elastic fracture mechanics of piezoelectric materials

Abstract: The concepts of linear elastic fracture mechanics, generalized to treat piezoelectric effects, are employed to study the influence of the electrical fields on the fracture behavior of piezoelectric materials The method of distributed dislocations and electric dipoles, already existing in the literature, is used to calculate the electro-elastic fields and the energy-release rate for a finite crack embedded in an infinite piezoelectric medium which is subjected to both mechanical and electric loads The energy-release rate expressions show that the electric fields generally tend to slow the crack growth It is shown that the stress intensity factor criterion and the energy-release rate criterion differ when the energetics of the electric field is taken into account The study of crack tip singular stress field yields a possible explanation for experimentally observed crack skewing in the presence of a strong electric field

Local and global energy release rates for an electrically yielded crack in a piezoelectric ceramic

Abstract: Structural reliability concerns of various electromechanical devices call for a better understanding of the mechanisms of fracture in piezoelectric ceramics subjected to combined mechanical and electrical loading. For these materials, due to unexplained discrepancies between theory and experiments, even the basic criterion of fracture remains a point of controversy. A viewpoint adopted in this paper is to model piezoelectric ceramics as a class of mechanically brittle and electrically ductile solids. As a first step toward understanding the effects of electric yielding, a strip saturation model is developed for a finite crack perpendicular or parallel to the poling axis of an infinite poled piezoelectric ceramics medium with electrical polarization reaching a saturation limit along a line segment in front of the crack. This model may be considered as a generalization of the classical Dugdale model for plastic yielding near cracks in thin metal sheets. The essential features of the strip saturation model are analyzed via a simplified electroelasticity formulation. Two energy release rates emerge from this analysis. An “apparent” or global energy release rate appears when evaluating J-integral along a contour surrounding both the electrical yielding strip and the crack tip. Under small scale yielding conditions, this energy release rate is equal to that of a linear piezoelectric crack without electrical yielding. A “local” energy release rate is obtained by evaluating J along an infinitesimal contour near the crack tip. The local energy release rate gives predictions which seem to be in broad agreement with experimental observations. It is also interesting that the local energy release rate is independent of the strength and size of electrical yielding.

Effect of electric field on fracture of piezoelectric ceramics

Abstract: Closed form solutions for all three modes of fracture for an infinite piezoelectric medium containing a center crack subjected to a combined mechanical and electrical loading were obtained. The explicit mechanical and electrical fields near the crack tip were derived, from which the strain energy release rate and the total potential energy release rate were obtained by using the crack closure integral. The suitability in using the stress intensity factor, the total energy release rate, or the mechanical strain energy release rate as the fracture criterion was discussed.