Technische Anwendungen des Lasers

Rosenberger, D.

doi:10.1007/978-3-642-93030-0

Cited by 28 publications

(5 citation statements)

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“…The scanning laser vibrometer has a high spatial resolution and needs no coupling media. The laser vibrometry is based on the Doppler effect [16]. If an object moves at a velocity v object toward the laser beam, the frequency of the light is shifted by the Doppler shift.…”

Section: Methodsmentioning

confidence: 99%

Continuous mode conversion of Lamb waves in CFRP plates

Willberg

Koch

Mook

et al. 2012

Smart Mater. Struct.

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Online damage detection in thin walled light weight structures with Lamb waves is one common way to develop structural health monitoring (SHM) systems. Lamb waves occur in multiple modes, which can convert into each other under special conditions. The effect of mode conversion of Lamb waves is a well known phenomenon. Typically mode conversion takes place at structural changes regarding the geometry and material, e.g. damage, cracks, delaminations, etc and can be used as a criterion to get information about the health of the structure. However, experimentally we observed an unexpected continuous mode conversion (CMC) of Lamb waves in a multi-layer composite plate partially made of fabric material, which means, e.g., that the symmetric S 0 -mode continuously converts into the A 0 -mode without passing a discontinuity. This effect causes a considerably more complex wavefield and makes the detection and localization of failures more complicated. In this work, the new phenomenon of CMC is described and investigated experimentally as well as numerically.

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Section: Methodsmentioning

confidence: 99%

Continuous mode conversion of Lamb waves in CFRP plates

Willberg

Koch

Mook

et al. 2012

Smart Mater. Struct.

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“…To determine the sign, the frequency of the reference beam is shifted through an acousto‐optic modulator (Bragg cell). This way, within a defined range, positive and negative velocities result in different beat frequencies, see [13, 16–18].…”

Section: Oblique‐angled Oscillations Observed With One‐dimensional VImentioning

confidence: 99%

“…For these reasons, it is worth to have a closer look on how the one‐dimensional set‐up can be used to obtain as precise information of the elliptic oscillation trajectories of Lamb waves. It is mentioned that the underlying three‐dimensional physical problem and the geometrical set‐up of the one‐dimensional experiment result in a systematic error that has to be added to the generally occurring errors, like speckle noise and dropout, thermal and photonic noise, thermal drift and gain error as well as offset error and bad positioning of calibration [1, 13– 16]. Of these, the latter two can be eliminated, respectively avoided, while others need to be decreased by statistical and filtering methods.…”

Section: Introductionmentioning

confidence: 99%

Identification and Avoidance of Systematic Measurement Errors in Lamb Wave Observation With One‐Dimensional Scanning Laser Vibrometry

Neumann

Hennings

Lammering

2012

Strain

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Scanning laser vibrometry is a widely used tool to observe Lamb wave fields for structural health monitoring (SHM) purposes. Lamb waves propagate over long distances in thin-walled structures and interact with structural inhomogeneities, for example, damages, in spite of wavelengths several times of the damage size. In SHM of sheets and glass-or carbon-fibre-reinforced plastic plates, this effect is used for determining the position as well as the size of structural faults. With the often employed one-dimensional vibrometry, a geometrically induced, systematic error occurs when measuring oblique-angled motion. This error can be, in the specific case of Lamb waves, of a non-negligible quantity. The nature of this geometrical measurement error in general and concerning Lamb waves in special is discussed analytically for both amplitude and phase data. It is shown that this matter should be taken into account in some applications.

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“…Um den Laserstrahl geometrisch zu charakterisieren, ist die Angabe des Strahlradius w, definiert durch den Abfall 1 der Intensität auf den Wert -j, üblich [6]. Wird diese Größe längs der Ausbreitungsrichtung gemessen, so läßt sich aus dem Verlauf auch die Fokustiefe z R (Rayleighlän-ge) bestimmen, die durch den Anstieg des Strahlradius auf den |/2-fachen Wert, von der Taille aus gemessen, definiert ist [7].…”

Section: Bestimmung Der Kennwerte Aus Dem In Tensitätssignalunclassified

Vermessung der Strahlgeometrie eines Laserstrahls im Mikrometerbereich mit Hilfe eines mechanischen Choppers / Measurement of the micron sized radius of a laser beam using two scanning edges

Werner¹

1991

tm - Technisches Messen

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Schlagwörter: Lasermeßtechnik, Laserfokus, Strahlgeometrie Die Lasermeßtechnik hat in den letzten Jahren Auftrieb erhalten. Speziell die optischen Verfahren zur berührungs-losen Rauheitsmessung werden immer häufiger eingesetzt. Die Größe des fokussierten Laserstrahls spielt bei diesen Meßprinzipien eine entscheidende Rolle. Es wird ein Verfahren vorgestellt, das sich zur Erfassung der Strahlgeometrie auch kleinster Fokusradien eignet. Progress had been made in laser metrology. Especially recent optical techniques for roughness measurements are used more frequently. The size of the focused laser beam has a great influence on the measuring result. A method is presented to get the geometrical properties of a focused laser beam.

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Technische Anwendungen des Lasers

Cited by 28 publications

References 0 publications

Continuous mode conversion of Lamb waves in CFRP plates

Continuous mode conversion of Lamb waves in CFRP plates

Identification and Avoidance of Systematic Measurement Errors in Lamb Wave Observation With One‐Dimensional Scanning Laser Vibrometry

Vermessung der Strahlgeometrie eines Laserstrahls im Mikrometerbereich mit Hilfe eines mechanischen Choppers / Measurement of the micron sized radius of a laser beam using two scanning edges

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