Vibration analysis of zinc sulfide and sapphire optical windows under bird strikes and airborne random vibrations

This study comparatively analyzed the vibration resistance of zinc sulfide (ZnS) and sapphire optical windows under bird strike (single-event impact) and airborne random vibration (cyclic loading) conditions to address the lack of research on these materials. The study used a validated SPH-FEM coupled model to systematically investigate the effects of impact angle and velocity on the response to bird strikes. A theoretical analysis of the random vibration response for both types of windows was also conducted based on acceleration power spectral density (PSD). The Miner criterion and the Steinberg method were applied to evaluate fatigue life. The results revealed significant differences in the vibration resistance characteristics of the two materials. Sapphire’s high stiffness results in a 65.9% lower vibration amplitude, ∼63% less internal energy absorption, and faster vibration decay post-impact compared to ZnS during bird strikes. However, its maximum stress doubles, indicating high stress sensitivity. Sapphire had a longer fatigue life under random vibration and a higher natural frequency. Conversely, ZnS exhibited exceptional energy dissipation due to its low stiffness. Its stiffness-energy absorption trade-off was significantly influenced by thickness. This study provides the theoretical and methodological foundation for selecting optimal window materials and structures based on specific operating conditions during the design phase. Sapphire is advantageous in applications that prioritize stability and a rapid dynamic response. At the same time, ZnS is superior in scenarios that require plastic deformation to mitigate high stresses or absorb substantial energy.