Concept and Objectives:
FANTOM proposes the development of an advanced NDT technique which combines thermography and holography/shearography which are both non-contact full-field optical techniques already applied in the aeronautical sector for composite structures inspection, each offering different advantages and disadvantages. The combination is envisaged on the basis of a unique measurement technique using a single sensor instead of a classical approach combining separate sensors which are correlated one to another.
A group of aeronautical industrials are already forming a club of end users to support this innovative technology of the next generation of NDT techniques. This club will contribute to the definition of industrial requirements and validation processes.
The FANTOM project will permit the development of a holography/shearography sensor with an usual optical set up, but instead of working at visible light wavelengths, it will work in the spectral range of thermographic cameras at LWIR (Long Wave InfraRed light) wavelengths.
The FANTOM project aims, through the LWIR holographic system, to achieve the following objectives:
- 20 times less sensitive to external perturbation than full-field optical strain measurement devices working at visible wavelengths.
- ability to measure 20 times larger displacement/strain, obtained under more realistic sollicitation levels than full-field optical strain measurement devices working at visible wavelengths. The full range of the tested component will be followed in real time. It will reduce the time of development because the non-destructive evaluation will be done countinuously during fatigue or static tests.
- ability to simultaneously determine thermal signatures (background image) and strain (holographic data = fringe pattern) which will be superposed in the resulting images.
- a 0% uncertainty in the correlation of thermal and strain measurement points through the unicity of the FANTOM sensor, whereas in the case of the correlation of 2 separate sensors an uncertainty of a few percents could be experienced due to different image sensor formats.
FANTOM Results in brief:
Increasing aircraft safety with better materials testing
Testing of aircraft components will soon be faster and more reliable. Scientists are developing a novel technology combining two systems in one for better evaluation of defects.
Non-destructive testing (NDT) techniques provide information about potential or existing defects in materials and parts without themselves damaging the parts. NDT is increasingly employed during the development phase in the aeronautics industry, saving valuable time and materials.
Optical non-contact technologies such as infrared thermography and shearography/holography have been widely employed. The former senses temperature distribution patterns that can be compared to temperature ‘signatures’ for identification of defects. The latter employ lasers to reveal target deformation and translation responses to an applied stress. These techniques enable wide-field assessment without dismantling, but typically rely on two different sensors.
Using state-of-the-art components, scientists are developing a novel one-sensor system with a shearography/holography sensor operating in the spectral range of an infrared thermographic camera. EU funding of the Fantom project is supporting scientists in their endeavour to decrease uncertainty, inspection time (one set-up and calibration instead of two) and post-processing to correlate deformation/temperature information. In addition, researchers are extending the range of displacement/strain measurement by a factor of 20, enabling an assessment of large deformations that was previously inaccessible outside controlled laboratory conditions.
Following selection of the appropriate holographic technique (electronic speckle-pattern interferometry (ESPI)) for combination with thermography (using a long-wave infrared laser (LWIR)), Fantom developed and built a portable prototype. It was tested and shown to enable visual inspection of large-scale deformations induced by high levels of disturbance, filling the sensitivity gap in current technologies. In a full-scale industrial case study of a large composite in a hangar, Fantom technology demonstrated enhanced defect detection capability when compared to two separate sensors.
Fantom has successfully delivered a mobile instrument capable of simultaneously measuring temperature and deformation with improved probability of defect detection over an extended deformation range. Fantom should be useful in aircraft development and maintenance as well as in numerous other sectors where large composite components are employed. These include the shipping, automotive and civil engineering markets.