Determination of second-order elastic constants of cyclotetramethylene tetranitramine (β-HMX) using impulsive stimulated thermal scattering

The second-order elastic constants for cyclotetramethylene tetranitramine (beta-HMX) single crystals were determined using the impulsive stimulated thermal scattering (ISTS) method. Despite the low symmetry of these crystals, the complete set of 13 elastic constants were determined accurately from acoustic velocity measurements using samples cut parallel to three different crystal planes. Our acoustic velocities are consistent with the limited sound speed data available from ultrasonic measurements. However, significant differences are observed between the elastic constants determined from our experiments and those obtained previously using Brillouin scattering. Our results demonstrate the usefulness and efficiency of the ISTS method for determining the full set of elastic constants of low-symmetry molecular crystals, including energetic crystals.