Impact Characteristics of Energy Absorbing Materials for Radioactive Material Transport Packages*

Energy-absorbing materials such as wood, grout, and polyurethane foams have been used as impact limiters in radioactive-materials transport packages to absorb kinetic energy in the event of an accidental impact. However, the dynamic behaviors of most of these materials are not well characterized or understood, especially at high impact velocities (V > 122 m/s). As part of a current program at Lawrence Livermore National Laboratory (LLNL) to evaluate package response during high-velocity impacts, a study to characterize several candidate energy-absorbing materials is being conducted. The impact study focuses on surfaces of two different hardnesses- unyielding and yielding. A soft-rock-type surface was chosen as a representative yielding surface in the study. Scaled package impact tests at velocities around 137 m/s on unyielding surface and close to 275 m/s on yielding surface were conducted. The particular point of interest is the dynamic behavior of materials having isotropic or nearly isotropic properties, such as grout (a mixture of sand and cement), high-density foam, and resin. This study excludes any anisotropic energy-absorbing materials such as wood, for even though wood is generally considered to be a good energy-absorbing material and is widely used as an impact limiter, its dynamic response at high impact velocities is difficult to predict using analytical means because of its inherent anisotropic structural properties.