Effect of scratches on the damage characteristics of fused silica optics under extremely-high impact load

Abstract

Fused silica glass is widely used in aircraft portholes, space telescopes, solar panels, etc. due to its excellent properties. In such environments, dust and debris with extremely high speed can easily create high impact loads on the silica glass surfaces, which would incur impact damage on the fused silica components and shorten their service life. Machining-induced surface defects on fused silica components would aggravate their damage behaviors, but the influencing rules and the underlying mechanisms has not been fully revealed. This work focuses on the influence of surface scratch defects on the impact damage characteristics of fused silica optics under the extremely high impact load. An improved Johnson-Holmquist Ⅱ (JH-2) dynamic constitutive model of fused silica was established on basis of the stress-strain relationship obtained by the Split Hopkinson Pressure Bar (SHPB) experiments. Based on that constitutive model, a dynamic simulation model describing the impact damage process induced by scratch defects was established by combining the smoothed particle hydrodynamics (SPH) algorithm and arbitrary Lagrange-Euler (ALE) algorithms. Then, the influence of scratch defect size on the impact damage morphology and crack propagation behaviors under various impact angles was systematically analyzed. The results show that, the impact damage induced by scratches with depths of 5 μm and 25 μm is more serious than scratches with other sizes. And under the impact angles of 45° and 60°, the damage extent of the optical surface with 10 μm-depth scratch is significantly lower than the defect-free surface. Finally, the laser-driven flyer experiment was performed to validate the role of scratch defects in influencing the impact damage characteristics of fused silica components under extremely high impact loads. The deviation between simulation and experimental results is generally within 10% except for one specific case that could be well explained, thus verifying the reliability of the established constitutive model and dynamic simulation model. This work could offer theoretical guidance and parameter basis for controlling the surface defects introduced in the machining processes and resultantly improving the impact damage resistance of fused silica components.