Experimental Wave and Material Property Measurements for an Elastomer Binder and Particulate Composite Material
The purpose of the work discussed here is to characterize the wave and material properties of polymer-bonded explosives (PBXs) at high frequencies. Knowing these properties could assist in the on-going development of methods for the detection and neutralization of improvised explosive devices (IEDs). The goal of this research was to experimentally measure these properties for mock energetic materials and develop a numerical model to replicate the experiment for the purpose of fully understanding and potentially bypassing the experimental procedures. Common materials science experiments were also performed on the materials studied in this work in order to maximize the fidelity of the numerical model by providing more accurate material properties. The end goal of this work was to have the capability to estimate the high frequency wave properties of energetic materials, solely by means of common materials science experiments and a numerical model. Prior work has provided comparatively few wave speed measurements for the binder materials commonly used with PBX materials. Furthermore, the measurements that have been reported are largely based upon rudimentary 'pitch and catch' methodologies, which involve sending a pulse from one transducer to another transducer, located a set distance apart, and measuring the time of flight. Given this, a more rigorous method for determining longitudinal and shear wave speeds in this important class of materials was desired. In this work, an alternative method for measuring material wave speeds is presented. The technique involved measuring the vibrational response along a line across the surface of a beam in response to a mechanical excitation, and then analyzing the data in the frequency-wavenumber domain via wavenumber decomposition. Wave speeds for a neat Sylgard 184 sample, a binder material for PBXs, and a Sylgard 184 composite sample (a mock energetic material) were measured and reported. In addition, the elastic wave behavior was simulated in a 2D numerical model of a neat Sylgard 184 beam to more completely understand the results of the experiment. The vibrational response was extracted from the model and the same wavenumber decomposition technique was applied to analyze the data in the frequency-wavenumber domain. Comparisons of the wave properties from the experiment and numerical model were made. Quasi-static tensile and dynamic mechanical analysis (DMA) tests were conducted on the neat binder and mock energetic materials. The results provided information on the influence of a mock energetic material's solids loading on material properties. Based on the resulting elastic moduli, the Poisson's ratio was calculated using the material wave speeds and densities also reported in this document. Overall, this effort provides important information on the wave properties of PBX materials at high frequencies. Going forward, the methods provided here have the ability to characterize additional materials and to assist in the development of more accurate numerical models for the purpose of predicting these wave properties. The wave properties provided in this work may assist in the development of IED detection and neutralization technologies.
Bolton, Purdue University.
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