Jürgen Ilg

Complete characterization of piezoceramic materials by means of two block-shaped test samples

We present an approach enabling entire characterization of piezoceramic materials. Contrary to the IEEE/ CENELEC Standard on Piezoelectricity, which is commonly applied for material characterization, the so-called inverse method requires only two block-shaped test samples. The method is based on a comparison of numerical simulations and measurement results for the frequency-resolved electrical impedance. Thereby, the aimed material parameters are iteratively updated so that simulations match measurements as well as possible. We utilize the identification procedure to characterize the piezoceramic material PIC255 as well as PIC155 from PI Ceramic, both of crystal class 6mm. In contrast to the parameters provided by the manufacturer, the identified data set leads to accurate simulation results for electrical and mechanical quantities of piezoceramic materials. This also holds if one predicts the behavior of geometrical shapes (e.g., disk) that are not considered within the inverse method. Moreover, we exploit the identification procedure to determine temperature dependences of the material parameters in the temperature range of -35°C to 130°C. To some extent, the parameters of PIC255 and PIC155 strongly depend on temperature. Nevertheless, the resulting electromechanical coupling factors for both materials remain nearly constant in the investigated temperature range.

Influence of the fabrication process on the functionality of piezoceramic patch transducers embedded in aluminum die castings

Piezoceramic patch transducers are integrated into aluminum components using high-pressure die casting. Expanded metal has proven suitable as a supporting structure for placing the patch transducers inside the die cavity and for stabilization during the injection of molten metal. However, difficulties arise when the transducers are positioned off the neutral axis within the wall of the casting. Numerical simulations of the die filling are performed to analyse the evolution of the integration process. The asymmetric infiltration of the supporting structure is identified as the major factor contributing to the formation of cracks and perforations inside the piezoceramic transducer. By means of measurements and numerical calculations of the electrical impedance of the transducer, a close relation is established between mechanical damage patterns observed in radiographs of the patch transducers and loss of performance.

Impedance-Based Temperature Sensing With Piezoceramic Devices

This paper deals with the temperature dependence of the electrical impedance of piezoceramic transducers. The behavior under thermal loads is investigated for bulk ceramics and composite structures where the piezoceramics are integrated into passive materials. According to these identified dependencies, temperature sensing through the piezoceramics impedance is realized using a polynomial fitting method. A creep operator and a lead filter are introduced to consider the time-dependent behavior of the electrical impedance. The presented approach is applied to a commercially available air ultrasound transducer. The accuracy of the measurement method is investigated for an arbitrary temperature profile yielding

Determination of Dynamic Material Properties of Silicone Rubber Using One-Point Measurements and Finite Element Simulations

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Enhancement of the inverse method enabling the material parameter identification for piezoceramics

. The presented method can be utilized for additionally sensing temperature in devices with integrated piezoceramic transducers, especially ultrasound transducers or in structural health-monitoring applications.

Identification procedure for real and imaginary material parameters of piezoceramic materials

The dynamic Youngs modulus, Poissons ratio, and the damping factor of silicone rubber are determined from a laser triangulation measurement of the top surface motion of a flat cylindrical sample excited by a shaker. These material parameters are estimated on the basis of an Inverse Method that minimizes the difference between measured data and a prediction from a finite-element model (FEM), in which the sought-after material data are the adjustable parameters. The results are presented for measurements within the 10-400-Hz frequency range under atmospheric pressure and temperature conditions. At first, the measured data are compared with FEM predictions using constant material parameters to show the material behavior in principle. Afterward, the frequency dependence of the moduli and Poissons ratios are determined by matching measurements with simulations within small frequency ranges. Finally, the material parameters determined are given as functions versus frequency. A sensitivity analysis shows the accuracy of the presented method. This paper is motivated by the need for a precise description of vocal fold models, commonly manufactured from silicone rubber.

Temperature measurements by means of the electrical impedance of piezoceramics

We present a mathematical Inverse Method providing reliable material parameters of piezoceramic materials. Thereby, a systematic matching of finite element simulations to measurements yields the complete set of material parameters. Contrary to our previous research where we utilized both, frequency resolved electrical impedances and spatially resolved surface velocities, only the impedance curves serve as input quantity of the enhanced Inverse Method. Within this method, two block shaped piezoceramics of equal geometric dimensions but different directions of electrical polarization are investigated. For the piezoceramic material PIC255, the identified material parameters exhibit to some extent deviations from the manufacturers parameters of more than 20 %. For verification purposes, we perform finite element simulations of a discoidal piezoceramic material which was not considered for the Inverse Method. Comparisons with measurements demonstrate that the identified parameters can be used to precisely predict the behavior of piezoceramic materials.

Inverse Methode zur Charakterisierung des mechanischen Frequenzverhaltens isotroper Werkstoffe

By means of numerical simulations, the efforts for the development of piezoceramic transducers can be considerably reduced. However, reliable simulations of the transducers behavior require precise material parameters which can not be obtained with common parameter identification methods. Therefore, we use an alternative approach to determine these parameters, the so-called Inverse Method. Basically, simulations and measurements for the frequency resolved electrical impedance and the spatially as well as frequency resolved surface normal velocity serve as input quantities. In this contribution, we present an extended Inverse Method enabling the determination of damping coefficients which are decisive for the description of dissipative losses in piezoceramic materials. The method is applied to a discoidal transducer made of Pz27. The results clearly show that the Inverse Method under consideration of the damping coefficients provides material parameters which can be used for reliable simulations of the transducers behavior.

Inverse scheme to identify the temperature dependence of electromechanical coupling factors for piezoceramics

This contribution deals with the temperature dependence of the electrical impedance of piezoceramic transducers. The behavior under thermal loads is investigated for bulk ceramics and composite structures where the piezoceramics are integrated into passive materials. According to this identified dependencies, temperature measurements by means of the piezoceramics impedance is realized using a polynomial fitting method. The accuracy of the measurements is investigated for different temperature profiles. The presented method can be utilized for additionally measuring temperature in devices with integrated piezoceramic transducers, especially in health monitoring applications.

Simulation based estimation of dynamic mechanical properties for viscoelastic materials used for vocal fold models

Zusammenfassung Es wird ein Verfahren zur Charakterisierung der Frequenzabhängigkeit der mechanischen Eigenschaften von Festkörpern (Viskoelastizität) vorgestellt. Insbesondere Kunststoffe zeigen häufig ein ausgeprägtes viskoelastisches Verhalten. Die Identifikation der frequenzabhängigen mechanischen Materialparameter erfolgt durch die Inverse Methode, welche auf der Anpassung von Simulationsergebnissen an zuvor durchgeführte Messungen beruht. Hierzu werden durch einen Optimierungsalgorithmus die Simulationsparameter schrittweise variiert. In diesem Beitrag wird eine angepasste Inverse Methode sowie die generelle Vorgehensweise der Materialcharakterisierung erläutert. Zudem werden viskoelastische Materialmodelle diskutiert und ihre Eignung anhand eines exemplarischen Werkstoffs geprüft.