Isolation Strategies of Carbon Nanotubes for Resistive Sensing in Carbon Fibre Prepreg Laminates
Topic(s) : Multifunctional and smart composites
Co-authors :
Tobias KARLSSON (SWEDEN), Per HALLANDER (SWEDEN), Malin ÅKERMO (SWEDEN)Abstract :
With the increased use of fibre-reinforced plastics (FRP) in the aviation, wind and naval sectors, the interest of performing reliable structural health monitoring of composite components has increased. Unlike metallic components, it is possible to embed sensors into the composite structure to perform in-situ measurements in real-time, monitoring the structure during its manufacturing and later its operational life. Optical and different resistive sensing methods are the two most studied methods, having different advantages. Whilst optical sensing methods are not affected by the electrical conductivity of its surrounding structure, this is very much the case for resistive sensing methods. Due to this, most work concerning in-situ resistive sensing in structural composites has been studied in glass fibre or other non-conductive fibre composites. To perform resistive sensing in a conductive carbon fibre composite, strategies to isolate the resistive sensor from the conductive carbon fibres are required. Modifications to the composite structure to isolate the resistive sensing should not degrade the mechanical properties of the laminate, nor degrade the sensing capabilities of the resistive sensor.
In this paper, isolation strategies of embedded Vertically Aligned Carbon Nanotubes (VACNT) into carbon fibre prepreg laminates are presented. VACNTs are reported to have the capability of performing cure monitoring and subsequent structural health monitoring in non-conductive glass fibre composite laminates whilst also being non-intrusive in the structure, not affecting the mechanical properties of the composite negatively. Requiring resin to infiltrate the interspace between CNTs to deposit the VACNT sensor, the VACNTs are normally deposited onto the prepreg surface. However, this is not possible in carbon fibre prepreg systems, leading to short circuiting of the sensor. Strategies has to be developed to avoid short-circuiting of the sensor whilst minimizing the addition of material and thickness of the laminate to preserve the mechanical properties. To this end, two isolation strategies are adopted. First, isolation using non-permeable films between the carbon fibre structure and VACNT sensor, preventing short-circuiting. The negative aspect of this method being the need to add resin onto which the VACNTs can be deposited, which adds thickness of the interlaminar region. Second, isolation using a porous separator, permeable to prepreg surface epoxy. Positive aspect being minimizing the amount of added material and being able to perform cure monitoring of the prepreg resin. The negative aspect of this strategy being the higher risk of short-circuiting the sensor. A comparative study is performed of the two strategies, discussing their ease of implementation and limitations. Later, the impact on mechanical properties of the laminate and the sensing capabilities of the isolated VACNTs are studied and compared to previous research.
In this paper, isolation strategies of embedded Vertically Aligned Carbon Nanotubes (VACNT) into carbon fibre prepreg laminates are presented. VACNTs are reported to have the capability of performing cure monitoring and subsequent structural health monitoring in non-conductive glass fibre composite laminates whilst also being non-intrusive in the structure, not affecting the mechanical properties of the composite negatively. Requiring resin to infiltrate the interspace between CNTs to deposit the VACNT sensor, the VACNTs are normally deposited onto the prepreg surface. However, this is not possible in carbon fibre prepreg systems, leading to short circuiting of the sensor. Strategies has to be developed to avoid short-circuiting of the sensor whilst minimizing the addition of material and thickness of the laminate to preserve the mechanical properties. To this end, two isolation strategies are adopted. First, isolation using non-permeable films between the carbon fibre structure and VACNT sensor, preventing short-circuiting. The negative aspect of this method being the need to add resin onto which the VACNTs can be deposited, which adds thickness of the interlaminar region. Second, isolation using a porous separator, permeable to prepreg surface epoxy. Positive aspect being minimizing the amount of added material and being able to perform cure monitoring of the prepreg resin. The negative aspect of this strategy being the higher risk of short-circuiting the sensor. A comparative study is performed of the two strategies, discussing their ease of implementation and limitations. Later, the impact on mechanical properties of the laminate and the sensing capabilities of the isolated VACNTs are studied and compared to previous research.