Inductance-based and inductance-capacitance-based structural self-sensing of shape-changing deformation in aluminum

Structural self-sensing refers to a structural material sensing itself without sensor incorporation. Resistance-based self-sensing has long been studied. This work addresses inductance-based self-sensing and inductance -capacitance-based self-sensing. In particular, it provides the first report of inductance-capacitance-based self -sensing. A change in the inductance causes a change in the capacitance. This is to be distinguished from the capacitance change resulting from permittivity change. Permanent mechanical deformation with shape change (such as that associated with bending or undulation, as opposed to tensile strain) increases the inductance, in accordance with Faraday's Law, thus decreasing the capacitance, as shown in this work for aluminum subjected to undulating bending. Conductivity is required for the inductance. The inductance capacitance is measured with the presence of a dielectric film (a double-sided adhesive tape) between the specimen and the aluminum foil electrode, as needed because an LCR meter is not designed for measuring the capacitance of a conductor. The specimen is subjected to undulating bending for different numbers of bends and different radii of curvature. The inductance and resistivity, as measured by direct clipping without the dielectric film, increase monotonically with the number of bends, while the inductance capacitance decreases monotonically. For radius of curvature 12.24 mm and 7.00 mm, the highest fractional increase in inductance (52% and 110%, respectively) is greater than the highest fractional increase in resistivity (2.2% and 7.3%, respectively) and the highest fractional decrease in inductance capacitance (2.04% and 2.4%, respectively). The sensing is superior for a smaller radius of curvature, whether the sensing is by measuring the inductance, resistance or capacitance. The inductance is superior to the resistivity or inductance capacitance for sensing bending.