Piezocomposite - Applications in Test Technologies
Due to the advancements of materials and components the test technology is faced with new challenges. Ever-increasing demands on the toughness require new techniques in the material testing sector. During the past years Piezocomposite Actuators have proven their worth. Especially the combination of force generation and dynamics of Piezocomposite Actuators from piezosystem jena provides a lot of advantages. This combination of benefits can’t be achieved by common drive concepts.
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Test procedures with increased test frequency
State of the Art
At mechanically test procedures like fatigue tests or analysis of the operational integrity the specimens are subject to high loads. Conventional test devices are able to generate a high force and determine a force-displacement-profile, however these devices are very limited in their dynamics. Currently higher test frequencies are generated in resonant-mode procedures. Resonance test machines, used in vibration tests at endurance tests, are driven electromagnetically or by servo-hydraulic systems. They can generate:
- Forces up to 1000 kN
- Frequencies up to 350 Hz
The frequencies can be changed by activating/deactivating the additional masses. Therefore the operating frequencies are limited to a certain number of steps.
Benefits of Piezocomposite Solutions
Piezocomposites are not bound to a fixed frequency as they work non-resonant. Stroke, signal shape and force generation are variable within certain limits.
- Variable frequency range up to 2 kHz
- Stroke up to 200 µm
- Forces up to 50 kN
The combination of force generation, load-bearing and dynamics enables high repetition rates. This leads to shorter test times and lowers the cost of test. Due to this fact Piezocomposite Actuators are suitable for:
- (Very-) High Cycle Fatigue Tests
- Endurance Test
- Fretting Tests
- Hardness Test
Modal analysis is used to characterize structures under vibrational excitation to gain information about different parameters like resonance frequencies or vibrational modes. It is applied in research and development as well as in the industry. With modal analysis the structural properties of components can be specified.
State of the Art
Components like casings or chassis are not able to generate vibrations. Hence, these components need an external vibration excitation. This can be achieved by:
- Impact hammers
- Electro dynamic/hydraulic shakers
- Unbalance motor
These methods have certain disadvantages. They lack reproducibility (impact hammer) and are restricted to low frequency operation.
Benefits of piezo-composite solutions
Piezo electric shakers form piezosystem jena are ideally suited to generate oscillations. With piezo electric shakers one can:
- Generate oscillations up to 100 kHz,
- Continuously tune through the possible frequency range,
- Generate accelerations up to several 10’000 m/s² (1000 g),
- Reproduce the oscillation parameters very accurately.
Other than ultrasonic transducers piezo electric shakers work non-resonant, but they can also be adapted to work at their resonant frequency or above. Due to the high energy density and the compact design piezo electric shakers can be used for body-sound-investigations at miniaturized components or at locations that are difficult to access.
An alternative approach for an acoustic resonance analysis consists of the use of piezo electrical shock generators. Thereby a short mechanical shock is generated and results in an excitation of a wide frequency band. In comparison to a continuous working piezo electric shaker the repetition rate and pulse power are decoupled. Another benefit of these shocks is their very high repeatability which can’t be achieved with impact hammers. One can generate shocks with:
- Pulse duration down to a few 10 µs
- Accelerations above 100’000 m/s² (10’000 g)
- Precise trigger-ability in the µs-range
Defect Analysis/Non-Destructive Testing
Another field of application for Piezocomposite Actuators is the Non-Destructive Testing, especially the Defect Analysis. Here Piezocomposites are used to generate oscillations or shocks. The wide frequency range enables the stimulation of different structures. Piezo electric shakers or shock generators can be used with frequencies ranging far into the ultrasonic range. Depending on the stimulated structure the response of the specimen can be determined by:
- Propagation time measurement
to obtain information about material characteristics or defcts.