Damage assessment of CNT-doped composites through IR-thermography and electrical resistance measurement

Abstract

Rooted in their heterogeneous microstructure, composite materials possess high strength-to-weight and stiffness-to-weight ratios, making them essential building blocks for a wide range of industrial applications. However, their complicated microstructure makes it difficult to predict the failure mechanism and residual life under varying external loads. The in-situ health monitoring system has received much attention in recent years as one of the promising solutions for the aforementioned limitations of composite material. In this research, we suggest a coupled health monitoring system where IR thermography and electrical resistance measurement are utilized simultaneously to diagnose the damage state of the composite materials during tensile testing. The deformation and failure timeline of GFRP under quasi-static tensile loading could be subdivided into three characteristic regions, here named as damage levels, characterized by i) elastic deformation without damage formation, ii) formation of distributed micro-damages, and iii) enlargement of concentrated damage. By employing a multiphysics simulation framework, we modeled the interplay between physical phenomena occurring in three damage stages, involving crack propagation, variation in the temperature profile and electrical resistance. The results also allowed us to have an estimation of the ‘damage stress(σD)’, a value that represents the onset of micro-damage, which has a negligible effect on the elastic properties, but might be dangerous under cyclic loading.