With the fast growing utilisation of composite materials in aircraft structures, manufacturers have to acquire appropriate non destructive testing systems. A large effort have been devoted for the last ten years to the improvement of two major techniques : ultrasonics and radiography. Up to now, these methods have been fully automated and their efficiency proven. However a demand exists for new methods which can offer a higher inspection rate than ultrasonics and can detect a wider range of defects than radiography. These considerations led us to look to thermography. Infrared non destructive testing is attractive since it requires no physical contact. It is potentially very rapide and easy to set up. It can be applied when only one side of a surface is accessible. Real time display and recording associated with image treatment make the interpretation of thermograms easy. A large investigation programme is carried out in order, to define the field of application of thermography to composite materials evaluation, to set up a method which can be industrialised, to write down specifications for an industrial installation. Thermophysical properties of the materials, different heat sources, infrared detectors and image processing systems are investigated. Calibration of the apparatus is also considered. An original method using the combination of a line heater, a line scanner and a real time digital signal processing and recording system is presented.
AbstractWith the fast growing utilisation of composite materials in aircraft structures, manufacturers have to acquire appropriate non destructive testing systems. A large effort have been devoted for the last ten years to the improvement of two major techniques : ultrasonics and radiography. Up to now, these methods have been fully automated and their efficiency proven. However a demand exists for new methods which can offer a higher inspection rate than ultrasonics and can detect a wider range of defects than radiography. These considerations led us to look to thermography. Infrared non destructive testing is attractive since it: requires no physical contact. It is potentially very rapide and easy to set up. It can be applied when only one side of a surface is accessible. Real time display and recording associated with image treatment make the interpretation of thermograms easy. A large investigation programme is carried out in order, to define the field of application of thermography to composite materials evaluation, to set up a method which can be industrialised, to write down specifications for an industrial installation. Thermophysical properties of the materials, different heat sources, infrared detectors and image processing systems are investigated. Calibration of the apparatus is also considered. An original method using the combination of a line heater, a line scanner and a real time digital signal processing and recording system is presented.
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