A smart sensing layer based on polystyrene and carbon nanoparticles has been developed. It has been deposited on the composite specimens for real-time, in situ monitoring of structural health. The strain response of the smart sensing layer has been recorded for composite laminates using different defect configurations (notch spacing). Numerical simulations of the stress-strain concentration have been carried out in order to determine the state of strain at the smart sensing layer, in the presence of different notch configurations. It has been observed that the sensing layer detects well the presence of large deformations and damage due to defects in the structure, with clearly defined peaks at the points of structural damage.

Graphene nanocomposites are constantly being explored for their applicability in the growing domain of strain monitoring (Jing et al. in Chin Phys B 22(5):057701, 2013) for real-time health and integrity assessment of structural parts. Strain gauges were manufactured by incorporating conductive graphene nanoplatelets (GNPs) in insulating polystyrene matrix by varying filler concentrations. Initial measurements showed that the resistance of these gauges decreases with increasing content of GNPs. For structural health monitoring (SHM) applications, these gauges were pasted on laminated glass fiber composite substrate. The specimens with integrated gauges were tested under monotonic tensile loading. The piezoresistive response of gauges was observed and registered as a means to detect strains in the composite specimens. The results presented in this paper demonstrate SHM capabilities of these smart strain gauges.

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In this article, we have explored screen printing as a fast and reliable process for the deposition of nanocomposite layer on glass fiber-reinforced plastic (GFRP) substrate for in situ structural health monitoring. The screen-printed sensor comprised of a thermoplastic matrix (high density polystyrene) and a dispersed nanofiller (carbon nanoparticles). Notches of different sizes (2.5 mm and 4.0 mm) were introduced to study the response of sensors to an existing damage. Stress concentrations were plotted across the width and the sensor results were correlated with the simulated stress concentrations to evaluate the response of sensors with respect to local stress concentrations. It was found that the screen-printed sensors responded to the stress concentrations since the layers were deposited in the vicinity of notches. The gauge factors altered due to the presence of notches indicating sensor sensitivity to the preexisting damage and resultant stress concentrations.

This study aims at developing the screen-printed sensors as a viable means of depositing sensing tracks on composites for their on-line structural health monitoring. Conventional silk screen was employed in order to deposit a nano-composite solution comprising of a conductive nano-filler (carbon nano-particles) dispersed in a thermoplastic matrix (high density polystyrene) on laminated composite specimens. The solution was deposited using a squeegee and was allowed to dry. Commercially available metal foil strain gauges were also bonded alongside screen-printed sensor in order to compare the response of the screen-printed sensors with the commercially available strain gauges. The sensing ability of these screen-printed sensors was tested on a universal testing machine (MTS 810) in four-point bending configuration using a load cell of 100 kN. The sensor deposited using screen-printing technique underwent tensile loading at the lower side of the laminate. A data linearization and amplification module comprising of commercially available instrumentation amplifier (INA 118) was used in conjunction with data acquisition module (Keithley KUSB 3100). The results obtained show that the screen-printed sensors have higher gauge factors in tensile loading scenario with reasonably linear response as compared to traditional metal foil strain gauges. The ease of the deposition of a nano-composite solution via screen printing also makes the technique a viable alternative to the traditional resin bonded metal foil strain gauges which have to be bonded on the surface. Moreover, screen printing offers unlimited options for the development of smart composites in various configurations for a multitude of structural applications.