N. Tralshawala, T. Batzinger, S. Nath, M. Gigliotti, GE Global Research Center, Niskayuna, NY; H. Robert, Quantum Magnetics, San Diego, CA
The measurement of component strain has been typically accomplished using strain gauges attached to the surface of the component. Recently, GE has been investigating the use of crystalline solids embedded in coatings such as paint or embedded through the volume of the component as part of the matrix material (i.e. embedded in the epoxy resin of composite materials) . To measure strain experienced by the component, NQR or nuclear quadrupole resonance techniques relying on the interaction between the nuclear quadrupole moment and a locally applied electric field (lattice field) gradient can be used for strain measurement. Some crystalline solids such as 14N, 35Cl, 37Cl, 63Cu and 65Cu have quadrupolar nuclei. Since the NQR frequency is directly related to lattice field, any perturbation that changes the local field properties, such as strain or temperature change will result in a NQR frequency shift. Detection of this shift enables ability to monitor strain in various structures and has the added advantage that the frequency shifts are independent of direction. This is especially important since in many applications where printed strain gauges or FBGs are employed, the strains normal to the fiber or coil direction cannot be detected. Applications such as bond integrity and structural damage detection are thus especially suited to NQR strain gauging. We will present data from some preliminary experiments conducted so far and exploration of applications in structural health monitoring.
