Monitoring of Mixed Failure Mode in <scp>CFRP</scp> Bolted Joint Structures Based on a Modular Piezoresistive Sensing Network

ABSTRACT Bolted joints in carbon fiber reinforced polymer (CFRP) structures are prone to mixed failures under complex loading conditions. However, existing structural health monitoring (SHM) techniques remain limited in capturing the whole progression of internal damage. To address this limitation, an embedded piezoresistive sensor was developed using a hybrid conductive filler consisting of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) at a mass ratio of 3:1. A spatially interconnected conductive network was established to improve sensitivity under complex stress conditions. Based on the distribution characteristics of failure regions, a modular sensor network was designed to enable real‐time identification of bearing‐tension and bearing‐shear mixed failure modes on CFRP bolted joint structures. Experimental results indicate that the mechanical performance of the structure remains essentially unaffected by sensor integration, and that resistance variation is capable of capturing structural state transitions under different failure modes. Specifically, during the bearing‐tension failure process, the relative resistance of Modules 1 and 2 increased to 17.9% and 9.0%, respectively, before decreasing to 10.0% and −4.6%, while in the bearing‐shear failure process, the resistance of Module 2 decreased from 754.8% to 167.4%. These findings present an effective approach for monitoring mixed failure modes in CFRP bolted joint structures.