Impulse excitation devices
The impulse excitation device function in the Impulse Excitation Technique is to excite the specimen natural frequencies of vibration with a mechanical impulse, generated from an impact. This impact must be controlled to avoid damage or moving. The impulse device can be manual or automatic and of different sizes and materials, according to the specimen characteristics.
An indispensable requirement for impulse devices is do not emit sounds or noises within the specimen frequency range. When applying, the device also receives the impulse by the action and reaction principle and is excited at its natural frequencies of vibration, which must be heavily damped and not coincident with the specimen frequency range.
Sonelastic® Systems have several impulse device options for small, medium and large-sized specimens in the geometries of bars, cylinders, discs, rings and also in complex geometries. In addition to the manual options, there are automatic models that ease impulse excitation procedure and allow automated measurements in dependence of time.
Manual impulse devices
Sonelastic® Systems have three models of manual impulse devices: Medium, Light and Extra Light Manual Impulse Device. All models have stainless steel impact tip, high-damping polymer body and comply with ASTM-E1876 standard.
ATCP Physical Engineering, Sonelastic® Division, also supplies custom impulse devices for large specimens, for example, precast concrete.
Automatic impulse devices
Sonelastic® Systems have the IED Automatic Impulse Device, which comprises a control unit and an electromagnetic impulse device. The following models are available:
- Light RT Impulse Device, for SB-AP support;
- Medium RT Impulse Device, for SA-BC and SX-PD supports;
- RTS Impulse Device, for SP-HZ support.
All electromagnetic impulse device models comply with ASTM-E1876 standard.
IED Automatic Impulse Device control unit allows the application of an electrical pulse of adjustable duration and amplitude in the electromagnetic actuator in order to shoot its tip against the specimen surface. The control unit is remotely operated by Sonelastic® Software by USB interface
The IED Automatic Impulse Device reduces the need for manual skill and allows automated characterizations in dependence of time, for example, to monitor curing processes.
To promote excitation, the impulse device tip must be shot against the specimen surface. At the impact, it occurs a momentary contact causing a force peak, or mechanical impulse, that excites the natural frequencies of vibration.
The mechanical impulse amplitude and duration determine, respectively, the specimen vibration amplitude and the excited frequency range. Vibration amplitude is directly proportional to intensity and frequency range is inversely proportional to impulse duration.
Influence of the impulse excitation intensity
The influence of the impulse excitation intensity on the elastic moduli result is usually negligible. However, a vibration amplitude too low may degrade the signal-to-noise ratio make it difficult to process the acoustic response. On the other hand, excessive excitation can displace or damage the specimen. In specific cases, for example, refractory materials damaged by thermal shock and rich in cracks and microcracks, the results non-linearity can be up to 1% [Ref]. To test if the specimen material is linear, simply repeat the measurement varying the intensity; if linear, the results must be identical within the frequency measurement uncertainty which is ±0.1%.
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Sonelastic® system for medium specimens
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