Houssein Nasser

Mixing Rules for the Piezoelectric Properties of Macro Fiber Composites

This article focuses on the modeling of structures equipped with Macro Fiber Composite (MFC) transducers. Based on the uniform field method under the plane stress assumption, we derive analytical mixing rules in order to evaluate equivalent properties for d31 and d33 MFC transducers. In particular, mixing rules are derived for the longitudinal and transverse piezoelectric coefficients of MFCs. These mixing rules are validated using finite element computations and experimental results available from the literature.

Directional dependence of the static response of layered piezoelectric transducers

Directionality of the static response of piezoelectric transducers is investigated in terms of strain and stress piezoelectric constants. Layered transducers that are composed of several orthotropic passive layers and one single active layer are considered. Both monolithic and composite piezoelectric layers are taken into account. Equivalent properties are derived via analytical mixing rules and validated towards a numerical homogenisation method. A design that guarantees maximum directional dependence in terms of strain piezoelectric constants is proposed. Transducer’s response in terms of directionality when it is mounted as a sensor patch on a mechanical structure is investigated.

Electric Field Distribution in Macro Fiber Composite Using Interdigitated Electrodes

In this paper, an attempt has been made to understand the electric field distribution in the Representative Volume Element (RVE) of the Macro Fiber Composite (MFC) using interdigitated electrodes IDEs. Since the magnitude of the electric field within the Representative Volume Element (RVE) using the IDEs is not uniform, an electrostatic study of the electric field behavior is carried out. An approximate RVE model with conventional electrodes, which is useful for the analytical solution, has been proposed instead of the RVE model with IDEs. Finally, the results obtained by the proposed analytical solution are compared to those obtained numericaly using the RVE model with IDEs.

Effect of Matrix Properties on the Overall Piezoelectric Constants of Piezocomposite Transducers

Macro fiber composites, or MFCs, consist of PZT fibers with rectangular cross sections embedded into an epoxy matrix. MFCs usually possess orthotropic electromechanical properties and are used as thin and conformable actuators/sensors. This article focuses on the development of a homogenized model for the behavior of MFCs. The effective properties of MFCs with interdigitated electrodes (IDEs) are determined analytically, using the uniform field method, and numerically in terms of the electromechanical properties of the fibers and the epoxy matrix. Results are given for different material properties of the matrix.

Static Analysis of Shear Actuated Piezo-Electric Beams via Hierarchical FEM Theories

Several one-dimensional finite elements for the static analysis of shear actuated piezo-electric three-dimensional beams are presented. A generic expression of stiffness and mass matrices is obtained through a Unified Formulation. The derivation is general regardless of the approximation order of the displacements and the electric potential over the cross-section and the number of nodes along the axial direction. A Lagrange’s polynomials based layer-wise approximation is used. Several mechanical boundary conditions and sensor and actuator configurations are investigated. Results are assessed towards three-dimensional finite element solutions. It is demonstrated that the proposed class of finite elements is able to yield very accurate results.

Toward Micromechanics of Coupled Fields Materials Containing Functionally Graded Inhomogeneities: Multi-Coating Approach

This article presents a micromechanics model for predicting the effective properties of coupled fields composite materials containing ellipsoidal multi-coated inhomogeneities. The model is based on Eshelbys theory of inclusion embedded in an equivalent continuum matrix. The main objective of this work is to build some numerical tools that will be useful for estimating the effective properties of composite materials containing functionally graded inhomogeneities. Two applications of the present micromechanics scheme to two-phase composite materials with electro-elastic and magneto-electro-elastic couplings are presented. The results are in a good agreement with experimental data obtained from the literature.

Dynamics and control in precision mechanics

This paper briefly describes three projects developed at the Active Structures Laboratory of ULB, in connection with precision mechanics. The first one considers the integration of piezoelectric fibers in composite structures for space applications; the second consists of an active piezoelectric bimorph mirror for adaptive optics, and the third considers the vibration isolation of sensitive payloads in spacecraft.