Fatigue failure of prefabricated crack HTPB(hydroxyl-terminated polybutadiene) propellant under strain control.

In an effort to elucidate the fatigue behavior of hydroxyl-terminated polybutadiene (HTPB) propellant with prefabricated cracks under strain-controlled conditions, a comprehensive experimental study was conducted employing an MTS fatigue testing machine. The experimental design included four cohorts of specimens: a control group of un-notched specimens and three experimental groups featuring notched specimens with prefabricated cracks oriented at distinct angles (0°, 45°, and 75°) relative to the horizontal. Throughout the duration of the fatigue tests, an infrared thermographic camera was employed to meticulously monitor the temperature variations across the surface of each specimen. The collected data revealed that an escalation in strain amplitude, when subjected to a constant frequency, is directly correlated with a decrement in the fatigue life of the HTPB propellant. Notably, the fatigue lives of the specimens with prefabricated cracks were observed to be congruent, culminating at approximately 210^4 cycles, and maintaining a consistent order of magnitude. Conversely, the un-notched specimens demonstrated a substantially more enduring fatigue life, extending to 110^6 cycles, thereby manifesting a cross-order phenomenon.Throughout the fatigue testing, the specimens exhibited a pronounced strain hysteresis effect, which is indicative of their pronounced viscoelastic attributes. Concurrently, the thermal monitoring of the specimens across the four experimental groups uniformly displayed an escalating temperature trend. Intriguingly, a positive correlation was identified between the final surface temperature and the fatigue life of the specimens, suggesting a potential interplay between the heat generated due to viscoelastic dissipation and the material's resistance to fatigue under cyclic loading.