Heat Generation in Particulate Composite Materials Induced By Direct and Indirect Excitation

<p dir="ltr">Mechanical excitation of particulate composite energetic materials is capable of producing a decomposition/deflagration event. For this reason, understanding the thermomechanical response of such materials and its relationship to material sensitivity is crucial to increasing safety in the manufacturing and handling of such materials. In this work, two different approaches were used in the process of exciting live polymer-bonded explosives (PBXs) and inert surrogates.</p><p dir="ltr">First, an indirect excitation method was used to further explore energy transmission across a high-impedance barrier and its secondary effects in heat generation. This method used sound sources, characterized using spherical acoustical holography (SAH), to impart periodic waves in the 2-20 kHz range onto an inert material. In addition, a numerical model was developed to project an arbitrary sound field into space. A material at a stand off distance was exposed to such sound field, increasing its surface temperature.</p><p dir="ltr">Next, a direct excitation approach was used to increase the material’s temperature and cause internal damage that could affect the material’s sensitivity. To achieve this, piezo- electric transducers capable of generating ultrasonic periodic waves in the 150-250 kHz range in the material were used. Near-field effects, as well as particle shape and size distributions, were studied to assess the effects that each hard on drop-weight impact sensitivity.</p>