Experimental Determination of Thermal Expansion Behavior in PBEs Using Digital Image Correlation Techniques

This study investigates the thermal expansion coefficient of polymer-bonded energetics (PBEs) using Digital Image Correlation (DIC), a non-contact optical technique capable of capturing full-field surface deformations. Cuboid specimens measuring 60 mm × 30 mm × 20 mm and composed of ammonium perchlorate (AP), polydimethylsiloxane (PDMS), and multi-walled carbon nanotubes (MWCNTs) were prepared with a high-contrast speckle pattern created by applying a white base coat followed by stamped black dots for optimal image correlation. The samples were heated to 80°C, held isothermally, and subsequently cooled to 0°C using liquid nitrogen. Axial strain extracted from the DIC measurements was used to calculate the effective thermal expansion coefficient for each formulation, and the results were compared with Voigt–Reuss theoretical bounds that incorporated the measured void volume fraction for each specimen. The thermal expansion coefficients obtained were (1.27 ± 0.05) × 10⁻⁴ °C⁻¹ for AP–PDMS, (1.05 ± 0.12) × 10⁻⁴ °C⁻¹ for AP–CNT 1%–PDMS, and (1.09 ± 0.10) × 10⁻⁴ °C⁻¹ for AP–CNT 2%–PDMS. These findings demonstrate that DIC provides a reliable method for quantifying thermomechanical behavior in PBEs and supports its use in the broader characterization of multifunctional energetic composites.