INSTRUMENT FOR IN-SITU MEASUREMENTS OF SPECIAL HULL TREATMENTS

An approch is proosed for the direct determination of a viscoelastic polymer's complex shear and compressional moduli using a dynamic durometer. The approach is an extensioin of the theory and instrumentation deveoped by NSWC. The proposed method involves measuring the impedance associaated with driving different radius indentors into the material, as a function of frequency. With multiple data points for the impedance as a function of endentor radius (at a given frequency), nonlinear simulataneous equations are solved to obtain all four constants of interest directly from the complete impedance relation for a radiating sphere in a viscoelastic medium. This approach will be demonstrated in Phase I. In addition, data acquisition time gating will be examined as a means of overcoming finite sample thickness issues. This will be supported by analytical theory development for radiation impedance in finite thickness materials. Because the proposed multi-indentor polymer characterization scheme uses the complete sphere radiation theory, it not only provides all of the complex moduli data, byt should improve accuracy over the present approach which relies on modeling the system with a single spring rate. This method will also be valid for frequencies beyond 1000 Hz.