Damage Detection in Composite Structures Using a Dielectric Signature Variation Approach

Abstract

Composite materials, constructed from a combination of fibre and resin, have rapidly emerged as a high performance alternative to conventional materials for new constructions as well as strengthening and repair of existing structures. However, the use of such materials may be accompanied by various types of damages and failure modes, including delamination, debonding, fibre rupture, and matrix cracking. This thesis presents a new nondestructive evaluation (NDE) technique for damage detection in composite structures. The concept, based on detecting local dielectric permittivity variations, was employed to design capacitance sensors with high sensitivity to detect such damages. An analytical and 2D finite element models were used to assess the influence of the sensor geometrical parameters on the output signals and to optimize the sensor design. Concrete and wood specimens wrapped with glass-fibre composites containing pre-induced defects with different types and sizes were constructed and inspected. The sensors were also used to detect the delaminations and water intrusion defects in pultruded composite members. The principles behind the sensor operation were also applied to detect other damages in other structures; the capacitance sensors were designed and used to locate ungrouted cells in a concrete masonry wall. The proposed sensors, coupled with a commercially available portable capacitance meter, facilitate employing this technique in the field for rapid inspection of composite structures without the need for sophisticated data analyses that are usually required by other more expensive and time consuming NDE techniques.