Applications de la thermographie infrarouge au controle non destructif des materiaux composites utilises en construction navale

Composite materials used in naval construction use mainly glass fibres and fabrics and epoxy resins for monolithic structures and syntactic foams or balsa wood for the core of sandwich structures. Traditional non destructive testing (NDT) methods such as ultrasonics or radiography do not always ensure a complete check of the structure, principally due to the strong heterogeneity of these materials. In order to improve this situation the DCN has developed a test method based on the use of active infrared thermography. The technique consists of illuminating the structure with a powerful lamp and observing the cooling of the surface with an infrared camera. Defects present act as obstacles to heat transmission in the material and cause thermal anomalies on the surface which are detected by the infrared camera. This method, developed initially in the laboratory as a prototype, is now used industrially in a DCN shipyard. This paper describes first the basic principles of the technique and laboratory applications. Two industrial applications are then presented, the control of deck structures at DCN Lorient, and the control of a glass-epoxy coating on a transmission shaft.