High Dynamic Testing Machines Based on Piezo-Ceramic Actuators for the Experimental Characterization of Materials and Components
M. Matthias1, T. Melz1, R. Wagener1, C. Lanz2
1Fraunhofer LBF, Darmstadt, Germany
2Isys Adaptive Solutions GmbH, Darmstadt, Germany
For the experimental simulation of high frequency dynamic loads up to the structural acoustic range, different test facilities like ultrasonic, resonant, electrodynamic or servo-hydraulic test machines have been developed in the last years and are in multiple use. But all of these machines have limitations either in the variability of the usable test signal, the level and precision of controlling the dynamic forces and / or displacements or the relation between static (preload) and dynamic test load.
Dynamic test machines used for material or component fatigue investigations with variable amplitude loading are usually based on servohydraulic actuators. These test machines are in widespread use but, due to current challenges in material testing especially with the service life enlargement in mind, they reach more and more their limit of usability due to their restricted testing frequencies.
The biggest disadvantage of servohydraulic test machines is the relatively small usable frequency range in the low frequency regime, which lies usually below a maximum of 50 Hz and is the limiting factor for the duration of the fatigue test and one of the reasons to stop the test runs at 1·10^7 cycles even no damages are noticeable.
With the focus to increase the test frequency significantly above the maximum frequency range of
servohydraulic test facilities, without having limitations in the characteristics of the usable test signal, different new test concepts and machines using unconventional actuators developed at the Fraunhofer Institute for Structural Durability and System Reliability LBF.
One of the main research areas at the Fraunhofer LBF is the structural durability and the experimental investigation of the cyclic material and component properties in order to characterise the material behaviour under cyclic service loading from the low cycle fatigue (LCF) regime up to the very high cycle fatigue (VHCF) regime, which means to apply usually up to 10^9 test cycles. Therefore, together with the Isys Adaptive Solutions GmbH, a new test machine based on piezoceramic actuators has been developed.
The standard piezo-ceramic actuator for this kind of test machines allows to generate forces up to +/-10 kN providing a usable stroke up to 1,0 mm peak to peak. Being integrated into a specifically designed test rig, which considers the structural dynamic incidents of high frequency testing, the test machine is able to generate test frequencies up to 1000 Hz, allowing to drive any arbitrary test signal which is a predominant advantages compared to any other test machines. In the case of VHCF research the test machine is able to reduce the necessary testing time compared to servohydraulic systems by factor 15 or more.
During the research of the fatigue in the different regimes from LCF to VHCF in the last 3 years the piezoceramic driven testing facility has shown an outstanding precision and reproducibility compared to the competing testing faciliticis with ultrasonic, servo-hydraulic or resonance power unit. Other fields of applications of piezo-ceramic test machine are investigations implemented to secure the reliability of micromechanical systems and connectors or to characterize elastomeric materials regarding to their dynamic/vibroacoustic properties.
ACTUATOR 2014 Manuscript A5.3
Publication date: 08/04/2015
Manuscript A5.3 published in Conference Proceedings ACTUATOR 2014
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