Structural health monitoring (SHM) has assumed an increasingly significant role in assessing safety and integrity of load-bearing composite materials in the civil and aerospace engineering. Glass and carbon fiber reinforced composites (FRC) have emerged as common replacement for metals in many structural components due to their high strength-to-weight ratio and fatigue resistance, although their failure mechanisms are complex and damage detection challenging. Therefore, several damage detection and monitoring methods have been investigated with different degrees of success. In particular, promising results have been obtained with techniques based on the measurement of the damage/strain-induced change in the electrical properties inherent to composite material or to an ad-hoc applied conductive coating.
In this work our objective is to produce a novel nanocomposite functional paint to be used as high sensitive piezoresistive coating for imaging of strain map and damage in composite structures through the electrical resistance tomography method (ERT). ERT is a sophisticated non-invasive imaging technique that uses electrical measurements made from a set of electrodes located along the periphery of the sensing skin to reconstruct the conductivity spatial distribution. The developed sensing skin will consist of a thin film of multilayer graphene nanoplateletes (MLG)-filled polymer that will be applied directly to the surface of the material to be monitored with a simple spray coating technique. The properties of the paint will be optimized by feedback from the morphological characterizations, adhesion tests, rheological and electrical measurements. Then, a 2D spatially distributed sensing skin, able to map damages and deformations over large areas, will be deposited on a FRC plate. The electrical measured data will be processed with an open source ERT matlab code (EIDORS) demonstrating the feasibility and potentiality of the proposed SHM system.
SHM is an extremely important methodology in evaluating the health of a structure by assessing the level of its deterioration and remaining service life. In fact, SHM market is estimated to reach US$ 3 billion by 2023 witnessing a compound annual growth rate of 30% over the period 2016-2023 [19].
In this context, the proposed novel piezoresistive graphene-based paint represents a promising material for strain and damage detection and localization in structures. In particular, the potential strategy for success is mainly based on the combination of a high piezoresistive, cheap and easily deployable coating filled with MLG (whose outstanding properties for strain sensing have been already demonstrated by the participants of the project in previous publications) with the superior imaging capability of ERT that can spatially resolve conductivity changes in nearly real time for low cost, requiring minimally invasive measurements.
In particular the project aims to pursue both scientific and technological achievements that represent a significant advance over the state of the art.
As it concerns the scientific goal the project is mainly aimed at understanding through microscopic investigations and electrical/mechanical experimental tests the correlation between the morphological/structural characteristics of the MLG-filled coatings and their macroscopic physical and functional properties (adhesion to substrates, conductivity, piezoresistivity). Regarding technological achievements, the target of the project is the fabrication of a ERT system based on a novel reliable proof-of-concept nanocomposite coating which is characterized by outstanding piezoresistive properties and which can be easily deposited over a large variety of straight/curved material structures with a simple spray coating technique.
Given the novelty of the present research, it is possible to foresee considerable margins for the submission of several articles in international high-impact Journals. The project has the potential to strongly impact the market of SHM in the near future, introducing a new cost-effective technology that will contribute to replace schedule-based inspection/maintenance of structures by condition-based maintenance,reduce life-cycle cost, and to improve safety of new and aging aircraft/aerospace/ civil structures.
[19] Structural Health Monitoring Market : Global Demand Analysis & Opportunity Outlook 2023