A critical component of hard and soft body armor testing is the utilization of a clay block behind the component being evaluated. One of the performance metrics used to evaluate products is the penetration depth into the clay of an indentation produced by a ballistic event. As the formulation and properties of the clay commonly employed in this application have changed over the years, it has become necessary to pre-condition the clay block test setup in an oven nominally set at 43 °C. Under this scenario, the performance of the clay block varies upon removal from the oven and subsequent cooling. To better understand the potential influence of this cooling on testing results, experimental studies have been conducted to determine a variety of thermophysical properties of the ballistic clay (Plastilina #1) and plywood used in constructing the clay block test frames employed in ballistic testing. Properties assessed included density, thermal conductivity, heat capacity, and emissivity. These measured properties have been subsequently employed in three-dimensional computer models to predict the heating and cooling response of the test setup when placed in or removed from the oven, respectively. The simulation temperatures achieved at various locations within the clay in the test setup have been compared to experimentally measured values at the same locations for several different heating, cooling, and cooling/reheating scenarios of interest. In general, the agreement between experimental and model results is reasonable, verifying that three-dimensional simulations can be employed to predict the thermal response of the test setup. The models have been further applied to investigate the influence of the metal (steel or aluminum) used as the exterior frame of the test setup and also to evaluate the potential performance benefits of incorporating a layer of polystyrene insulation between the clay and metal frame.
Citation: NIST Interagency/Internal Report (NISTIR) - 7840
NIST Pub Series: NIST Interagency/Internal Report (NISTIR)
Pub Type: NIST PubsReport Number:
Ballistic clay, convection coefficient, heat capacity, thermal conductivity, thermal modeling, thermal properties.