Strain Measurement on a PBX during Temperature Cycling Using Fibre Bragg Gauges

The anisotropic and irreversible expansion properties of polymer-bonded explosives (PBX) can significantly influence the utility and reliability of associated equipment. The physical state of PBX under temperature cycling affects the strain distribution across the surface of cylindrical specimens. This strain is indicative of the irreversible growth and anisotropic expansion of the specimens. In this study, fiber Bragg grating sensors are employed to monitor the strain of PBX throughout the temperature cycling process, and our focus was on analyzing the changes in anisotropy and strain distribution during the cycle. The relationships between strain, temperature, material properties, and differences among various materials are examined. Experimental results indicate that the strain along the height and radial directions of the PBX specimens displayed a monotonic gradient distribution, increasing progressively in areas of higher density. TATB-based PBX exhibited anisotropic expansion throughout the temperature cycling, with the degree of anisotropy increasing during heating and decreasing upon cooling. Conversely, HMX-based PBX showed greater expansion in the height direction during both the heating and cooling phases, but it did not display noticeable anisotropy following the temperature cycling. At the highest temperature-holding stage (100°C), the HMX-based PBX was isotropic. The extent of strain in PBX was correlated with the thermal expansion coefficient of the crystal, although the final degree of expansion was not dependent on the initial range of strain. The ratchet growth of TATB-based PBX was approximately 31 μϵ greater than that of HMX-based PBX.