A novel NDE approach towards evaluating adhesive bonded interfaces

Aerospace structural components are made by adhesively bonded layers of different materials for achieving specific properties for industrial applications. One such advanced structural material is made of glass fibre reinforced plastic (GFRP) composite. This is a layered engineered material with composite adhesively bonded to rubber to one of the surfaces. Such engineered materials can withstand structural, thermal and corrosive environments. GFRP composite have to be bonded with rubber using rubber solution or other adhesive to keep them structurally bonded. Any separation of these two layers will make the engineered structure redundant. In this paper, we report application of various NDE methods for evaluating bonded interfaces of engineered structural composite materials. Conventional methods such as X-ray radiography and ultrasonic (acousto-ultrasonic) methods were experimentally verified for identifying defects at the adhesively bonded interfaces. Disadvantages of these conventional methods were overcome by using advanced single sided nuclear magnetic resonance (NMR) technique. The use of low frequency single sided portable NMR for characterising defects at the adhesively bonded interfaces is discussed. In addition to the defect detection, application of NMR for measuring thickness of adhesive layers coated over rubber is also presented. Advantages of using NMR technique over other conventional methods is discussed.