Local defect resonance excitation thermography for damage detection in plastic composites

Ultrasonic excitation thermography testing (UTT) is a well-established non-destructive testing (NDT) method that excels in its high defect selectivity in very short measurement times. The former is advantageous for providing clear and user-friendly results. Especially in the case of cracks and crack...

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Bibliographic Details
Main Authors: Rahammer, Markus, Kreutzbruck, Marc
Format: Conference Proceeding
Language:English
Subjects:
Broadband
Crack tips
Damage detection
Defects
Destructive testing
Energy management
Excitation
Flooding
Fracture mechanics
Frequency ranges
Nondestructive testing
Polymer matrix composites
Power management
Resonant vibration
Selectivity
Thermography
Transducers
Ultrasonic testing
Ultrasonic welding
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Summary:Ultrasonic excitation thermography testing (UTT) is a well-established non-destructive testing (NDT) method that excels in its high defect selectivity in very short measurement times. The former is advantageous for providing clear and user-friendly results. Especially in the case of cracks and crack-like defects like delaminations, a defect signal can be expected after just a few seconds independently of the material tested. While common ultrasonic testing devices use high frequencies (MHz), UTT typically utilizes high power sonotrodes with kHz-frequencies adopted from the ultrasonic welding industry. Usually high electric and acoustic powers are necessary to provide sufficient energy to the defect. The principle of local defect resonance opens up new methods to significantly reduce the energy required and enables the employment of small piezo-based transducers. Defects are modelled as distinct volumes with a fixed mass and geometry that have their own resonance frequencies. Flooding the specimen with ultrasound of that frequency leads to a distinct excitation of the defect vibration while the residual specimen area is resting. Due to the small mass vibrating only a very small amount of excitation energy is needed. This energy-efficient excitation due to the resonant vibration can be used for UTT, because all common heating mechanisms (hysteresis, crack tip friction) respond. Experiments have shown that acoustic energies in the range of mW suffice, in order to produce temperature increases greater than 1 K. The largest hindrance so far has been the determination of LDR frequencies of unknown defects. However, the upper and lower limit of these frequencies depends on the material and the defect size and is known due to a large experimental base. Using a broadband sweep excitation in this frequency range this method can be applied even to unknown parts with delaminations of few mm size and bigger.
ISSN:0094-243X
1551-7616
DOI:10.1063/1.5084894