Keywords: piezoelectric composites, advanced materials, porous, numerical simulation, homogenization, finite element analysis.

Porous piezocomposites are a class of recently developed "smart" or "intelligent" materials used as hydrophones, sensors, actuators in various applications in diverse areas such as bio-medicine, aerospace, NDT, etc. (see e.g. Newnham [1]). Porous piezocomposites are of two types: one with 3-3 connectivity (opened porosity) and the other with 3-0 connectivity (closed porosity). In this paper we consider a 3D porous piezoelectric composite model and investigate the effective electro- mechanical properties of the composite for different applications. More specifically, we consider a three-dimensional cubic body made-up of a piezoceramic material with air inclusions (pores), which are randomly distributed in the material (this is a piezoelectric porous non-periodic composite with 3-0 connectivity).

To analyze the effective moduli of this material we employ non-periodical homogenization (see Horoshun [2]) and the finite element technique (see Getman [3]). This complex approach allows us to consider the heterogeneous porous piezocomposite material as a homogeneous one with the new (effective) moduli. We consider only a 3D representative composite volume (RCV), which has many spherical pores located randomly, where the pores are described geometrically by spherical shape iso-parametric elements. For this domain (RCV) we present a methodology for finding all the effective moduli, and study the behaviour of important effective characteristics for hydrostatic and oscillation applications.

As a result all the effective moduli of the porous 3-0 piezocomposites are obtained, on the basis of which we have considered several important hydrostatic and oscillation effective characteristics. The results show us that the porous piezocomposites with 60% of porosity have comparative values of hydrostatic electromechanical coupling factor and that hydrostatic coupling coefficients increase by three times, that the hydrostatic voltage coefficient increases by more than five times, and that the figure of merit is fifty times more than with a pure piezoceramic one. It is evident that the piezoelectic sensitivity of porous piezocomposites is higher in comparison with one of pure piezoceramic. Therefore, the porous 3-0 piezocomposites with 60% porosity are very appropriate for hydrostatic applications.

What is it about the high-frequency applications (actuators), that makes a porosity of 40% very suitable? It is because in this case the electromechanical coupling factor has approximately the highest value, and the acoustic impedance is two times less than the properties of pure ceramic. It is well known that such properties of materials are most optimal for oscillation applications.

Therefore, we present a general hybrid computational method for the modelling of 3D porous piezocomposites based on the finite element and non-periodical homogenization methods. We consider a representative composite volume with randomly located pores, which are described by spherical iso-parametric elements and compute the effective moduli characterizing a particular (3-0) piezocomposite material, i.e. we study the behaviour of the hydrostatic and oscillation properties of the material, on the basis of which we show the superior properties of the porous piezoelectric composites.

1

Tressler J.F., Sedat A, Newnham R.E., "Piezoelectric sensors and sensor materials", J. of Electroceram., 2(4), 257-272, 1998. doi:10.1023/A:1009926623551

2

Horoshun L.P., Maslov B.P., Leshchenko P.V., "Prediction of the effective properties of piezoelectric composite materials", Kiev: Naukova Dumka, USSR, 1989. (in Russian)

3

Getman I., Lopatin S., "Theoretical and experimental investigation of the porous PZT ceramics", Ferroelectrics, (186), 183-189, 1996. doi:10.1080/00150199608218088

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