Bonding Analysis of Layered Materials by Photothermal Radiometry

Photothermal radiometry is a promising method for the non-destructive testing (NDT) and characterization of thin materials and has already been suggested for studying various kinds of layered materials. A bonding defect at the interface of two materials leads to a thermal contact resistance which is usually low and hardly detectable with the existing NDT techniques. The results of three studies of modulated photothermal radiometry for which such defects can be observed are presented. First, several metallic, electrochemically induced deposits have been studied. A statistical treatment allows various samples prepared under different conditions to be distinguished. Then, a similar coating (black polyurethane paint) has been deposited on two plates (steel and glass) for which the bonding strength is known to be different. Evidence is given of the existence of an interface thermal resistance for the coating deposited on glass. Finally, the mechanical contact quality between two coaxial metallic pipes has been studied. A mathematical model has been developed which includes a focused laser excitation. In this way, very low contact resistances ( approx 10 exp --5 m exp 2 K W exp --1 ) can be measured. Graphs. 5 ref.--AA