Abstract

Adhesive joints have widespread applications in aerospace and automotive industries, but predicting catastrophic failures during dynamic loads is very difficult due to the inaccessibility of the bonded interface. We have developed a new technique based on carbon nanotube (CNT) sensors that can monitor the bond integrity and is capable to predict failure well in advance. The conductive network inside the adhesive is very sensitive to crack initiation, propagation and delamination, therefore in-situ measurement of the bond resistance is capable of recording events that lead to failure. In 90% of the samples the change in bond resistance remains below 10% of the initial value up to approximately 80% of the fatigue life, and then the resistance increases rapidly due to crack propagation and interfacial delamination. As the increase in resistance typically occurs over a few hundreds to thousand cycles it is possible to define a resistance that corresponds to a safety limit before catastrophic failure. Moreover, the addition of 1 wt% MWCNTs inside the adhesive increased the joints shear strength and fatigue life by 10% and 20% respectively. The decrease in electrical resistance due to addition of only 0.5 wt% was more than 7 orders of magnitude.