NDE OF HONEYCOMB STRUCTURE: A COMPARATIVE STUDY OF INFRARED AND TERAHERTZ IMAGING

The honeycomb type material is one of composite materials. This type of material consists of core which is 3-dimansional structure having a form of combined hexagonal cells like the structure of honeycomb. Each side of the core is covered by layers of different material. These composite materials were mainly used in aircraft industry at first but they are also used in following domains now: aerospace, marine, automotive, railways, medical, architectural, electronic engineering, pharmaceutical, food and sport-recreation. These materials can be made both from metal and non-metallic materials. Typical defects are: faults like cracks, destruction in covering layers, destruction of core and separation of covering layers from core. In the past years, terahertz (THz) technology has received more interest and attention because of its unique properties and capabilities that make it very attractive as a non-destructive evaluation (NDE) tool (Redo-Sanchez, 2006). Most items consisting of dielectrics like plastic, glass fiber reinforced plastics (GFRP), ceramics and certain composites (e.g. GFC) are transparent for THz waves, whereas, metals and other conducting materials such as carbon fiber reinforced plastics (CFRP) are not transparent for THz waves (Ewers, 2010, Jonuscheit, 2010). This paper presents a comparison results from Terahertz (THz) and IR imaging for non-destructive testing non-metallic composites. The research was carried out by both transmission and reflection mode. Advantages and limitations of these methods are discussed.