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Investigation of the dynamic behaviour of the 250 kN shock force calibration device

01.01.2013

In the scope of the characterization of the dynamic behaviour of this calibration device with a mounted force transducer, different experimental measurements were carried out and the strongest modal oscillations were identified. Using the example of a heavy force transducer of 25 kg, the observed modal behaviour was confirmed by finite element modelling. Further experiments showed that the coupling resonance of the mounted transducer strongly depends on the mechanical adaptation and the mounting torque applied.

Experimental tests at the 250 kN shock force calibration device commissioned in 2010 showed that short force pulses (of about 1 ms) may excite strong modal oscillations in the lower kilohertz range. For instance, the lowest axial modal oscillation of a force transducer (device under test) of 25 kg mass and a specified fundamental resonance of 6 kHz could be observed at about 1.4 kHz. This low-frequent oscillation possibly strongly limits the usable frequency range for shock force calibrations.

To characterize and optimize the dynamic behaviour of the measuring device, the modal oscillations of the device were experimentally determined [1]. For this purpose, the signals of miniature acceleration sensors applied at spots of interest were acquired as well as those of the force transducer and the two laser interferometers measuring the shock acceleration of the two 100 kg mass bodies. It was possible to identify the axial modal oscillations below 10 kHz by analysing the signal ringing in the time and frequency domain. Finite element modelling of the impacting mechanical structure excellently confirmed the experimental results. Significant deviations were only noticed for the coupling resonance of the force transducer mounted to the mass body. The model predicts a higher coupling stiffness resulting in a higher resonance frequency. Further experiments showed that the coupling resonance strongly depends on the constructive design of the adaptation and the applied mounting torques [2]. It is now planned to raise the coupling resonance frequency by modifying the adapter design.

The investigations presented were carried out in the scope of the current EMRP research project IND09 dedicated to the dynamic measurement of mechanical quantities (force, pressure, torque) [3, 4].

Figure 1: Investigation of modal oscillations of the mass body with mounted force transducer

References:

[1] M. Kobusch, L. Klaus, T. Bruns: "Model-based analysis of the dynamic behaviour of a 250 kN shock force calibration device", XX IMEKO World Congress, 2012, Busan, Republic of Korea, Link

[2] M. Kobusch: "Influence of mounting torque on stiffness and damping parameters of the dynamic model of a 250 kN shock force calibration device", 7th Workshop on Analysis of Dynamic Measurements, 2012, LNE, Paris, France

[3] C. Bartoli et al.: "Traceable Dynamic Measurement of Mechanical Quantities: Objectives and First Results of this European Project", XX IMEKO World Congress, 2012, Busan, Republic of Korea, Link

[4] Homepage of the Joint Research Project “Dynamic Measurement of Mechanical Quantities” EMRP IND09: Link

Contact person:

Michael Kobusch, Dept. 1.7, WG 1.73, e-mail: michael.kobusch@ptb.de