# Evaluation of Fatigue Damage Monitoring of Single-Lap Composite Adhesive Joint Using Conductivity

## TL;DR

This paper explores using electrical resistance changes to monitor fatigue damage in adhesive joints, finding that resistance change correlates with debonding in two distinct ways linked to different failure mechanisms.

## Contribution

The study identifies two distinct micromechanisms affecting resistance change in adhesive joints during fatigue, offering new insights for structural health monitoring.

## Key findings

- Debonded area correlates linearly with fatigue life but shows two distinct resistance change trends.
- Scanning electron microscopy reveals different micromechanisms behind the two resistance change trends.
- The findings suggest practical implications for using resistance change in structural health monitoring.

## Abstract

The widely used adhesive joining technique suffers from the drawback of being unable to be dismantled to examine for degradation. To counteract this weakness, several structural health monitoring (SHM) methods have been proposed to reveal the joint integrity status. Among these, doping the adhesive with carbon nanotubes to make the joint conductive and monitoring its electrical resistance change is a promising candidate as it is of relatively low cost and easy to implement. In this work, resistance change to monitor fatigue debonding of composite single-lap adhesive joints has been attempted. The debonded area, recorded with a liquid penetrant technique, related linearly to the fatigue life expended. However, it correlates with the resistance change in two different trends. Scanning electron microscopy on the fracture surface reveals that the two trends are associated with distinct failure micromechanisms. Implications of these observations on the practical use of the resistance change for SHM are discussed.