Application of Field Mapping in Enhancement of Eddy Current Inspection

Abstract

The field of Nondestructive Evaluation is currently growing. Any engineering system requires NDE throughout its functioning life. Typical examples are found in aircraft, motor vehicles, pipelines, bridges, trains, power station, refineries and oil platforms which are all inspected using NDE. There is trend now to think of NDE while system is in the design stage. This is known as design for inspectability . which makes use of advances in smart materials to make systems easier to be handled tens of years after their construction. NDE thus become large umbrella that covers engineering system life from design phase, manufacturing phase, maintenance phase, up to the date on which system is retired.

Eddy current methods of nondestructive testing (NOT) are widely used in various industries for characterization of materials and detection of flaws. Analytical approaches to the modeling of electromagnetic field/defect interactions have largely been unsuccessful due to the awkward boundaries associated with realistic three dimensional defect shapes and the need for restrictive simplifying assumptions in order to obtain tractable analytical solutions.

Numerical models based on finite element formulation of classical Maxwell's equations in differential form have the ability to overcome the difficulties encountered in analytical and integral equation models.

The thesis introduced a computational model based on nodal-based finite element to model real problem such as crack initiating under the cap of an aircraft fastener. Due to problems associated with nodal-based finite element method in modeling electromagnetic problems the thesis adopted a new technique using edge-based finite element to model eddy current testing problems. Edge-based finite element is an enhancement of the finite element method.

Eddy current inspection instrument is developed in this thesis. Results of finite element computational model proposed are compared with the measurements obtained by the proposed eddy current inspection instrument. Encouraging results were obtained.