TITLE: Application of Microwave Nondestructive Testing and Evaluation to Thick Composites

Abstract:
(Introduction) The ability of microwave to penetrate inside dielectric materials makes microwave NDT&E techniques very suitable for interrogating structures made of thick composites. Additionally, the sensitivity of microwaves to the presence of dissimilar layers in such materials allows for accurate thickness measurement and variation detection.

Microwave NDT techniques as they pertain to thick composites may be conducted on a contact or noncontact basis, in addition to the fact that these measurements are conducted from only one side of the sample (reflection techniques). Furthermore, when compared with ultrasonic techniques, microwave NDT approaches require no coupling material (glass or water), and do not suffer from signal attenuation due to the grain size problems.

Microwave NDT techniques are also easily adapted to on-line measurement environments which afford the possibility of process control during the manufacturing of composites so that the final product may not need any scrutiny and may only require occasional testing once under some loading. Microwave NDT techniques are also capable of material characteristic interrogation, particularly when detecting the effect of curing. Therefore, the potential of testing adhesive for proper curing during manufacturing is very high.

Microwave techniques may also be used for determining the constituent components of mixtures. Furthermore, correlation of measured microwave data to physical and mechanical attributes of a structure are also possible. These techniques are able to detect voids, delaminations, porosity variation in a variety of materials as well as impact damage. The polarizability of microwave signals and microwave sensors provides for detecting fiber Disorientation during the manufacturing which may lead to eventual degradation of a composite structure. The same feature may also provide information about cut or broken fiber bundles inside a composite member. Defect sizing is also an important feature associated with microwave techniques. Finally, microwave NDT techniques do not require a high level of expertise from an operator, and can be conducted on-line and in real time with simple hardware which may be handheld and battery operated.

Source: Proceedings of the 'NDE applied to Process Control of Composite Fabrication' - Conference, 4-5 Oct 1994 St. Louis, Missouri. Publisher and Organizer: Nondestructive Testing Information Analysis Center (NTIAC) Texas Research Institute Austin, Inc. Austin, Texas [http://www.ntiac.com] [Buying the Proceedings]