Nuclear magnetic resonance imaging of damage and defects in fibber-reinforced polymer matrix composite laminated coupons and real-scale components with a single-sided sensor (NMR-MOUSE)

Abstract

Nuclear Magnetic Resonance (NMR) provides non-invasive imaging by using the endogenous contrast of materials, regardless of their optical opacity. This technique has been widely used to ascertain physical parameters such as diffusion and flow in porous materials and biological tissues, probing length scales from nanometres to meters (Blümich et al., 2008). More recently this potential non-destructive method was successfully applied to detect, identify, discriminate and quantify typical liquid contaminants of in-service aircrafts like water, jet fuel, hydraulic fluid and deicing entrapped in honeycomb core cells of structural composite sandwich panels (Portela & Tarpani, 2010), as well as to imaging moisture/water in solid fibre-reinforced polymer matrix composite laminates (Kotsikos et al., 2007). In either case, the samples were brought into the laboratory to be investigated with radiofrequency waves generated inside huge and massive stationary magnets. Therefore the concept of portable (mobile) single-sided NMR could lead to a new perspective for the non-destructive inspection of components and structures made with polymer matrix composites reinforced with continuous high performance fibres. The development and operationalization of mobile NMR devices can provide a real-time evaluation alternative to in-field integrity assessment of aeronautical and wind-power structures made with composite materials, besides to allow one envisioning its application as a non-destructive testing technique in other high-demanding fields like, for instance, in periodical, non-invasive, in-vivo inspection of composite-made structural implants in humans. The NMR-MOUSEÒ, or the MObile Universal Surface Explorer developed at Aachen University in Germany, is a hand-held NMR sensor that allows measurement of NMR relaxation parameters in surface-near solid volume elements of arbitrarily large objects in low and inhomogeneous magnetic fields. The NMR-MOUSEÒ basically consists of a permanent magnet and a frequency coil, arranged in such a way that an NMR signal can be collected from outside, the device in the stray-field of the magnet and the coil. Sensors like the NMR-MOUSEÒ provides enough support to be a potential method to assess damage and fracture in fibre-reinforced polymer matrix composites used, for instance, in both the aeronautical and the human implant fields. NMR-MOUSEÒ results in good image definition due to its high gradient and exceptionally short echo time that can be used for measuring transverse relaxation decays (Blümich et al., 2008; Blümich et al., 1998; Eidmann et al., 1996). The main objective of this BEPE-FAPESP project is to assess the ability and capability of NMR-MOUSEÒ to indicate, locate, qualify, and quantify damages and fractures in solid laminates of carbon fibre-reinforced thermoplastic and thermosetting matrices utilized not only in the manufacturing of structural human implants (wet-conditioned samples testing), but also in real-scale aircraft components (dry-conditioned samples testing). For this purpose, several composite-made test coupons and real-scale structural pieces were manufactured in Brazil, with some of them already examined by the BEPE-FAPESP candidate through Nuclear Magnetic Resonance Imaging techniques during her first semester of activities by IC-FAPESP program, and will be taken to the Aachen University in Germany. The BEPE-FAPESP candidate plans to pursue in the near future a Doctoral position along with the Research Group in Macromolecular Chemistry led by Professor Bernhard Blümich in Aachen University, so opening an opportunity for the establishment of a prolific and long-lasting partnership between RWTH-Aachen and her origin institution (EESC-USP), represented by the Structural Composite Materials and Non-Destructive inspection Group coordinated by her former supervisor, Associate Professor 2 José Ricardo Tarpani. (AU)