Application of High-Speed DIC to Study Damage of Thin Membranes Under Blast

Abstract

High-intensity impulsive sounds caused by high-amplitude blast pressures (e.g., explosion or large caliber military ordnance, etc.) may damage the human eardrum and produce conductive hearing loss. But little is known about sound-matter interaction during rupture of the eardrum. In this study, thin membranes (Teflon sheets) with orthotropic material properties resembling the human eardrum are ruptured by air pressure loading produced with a custom-made apparatus. The orthotropicity of the membrane was verified and measured with scanning electron microscopy and micro-tensile tests. Two calibrated high-speed cameras in a stereo configuration measured 3D surface displacements of the membranes during rupture using a digital image correlation (DIC) method at framerates as high as 1.2 million fps. DIC results show the mechanics of rupture can be divided into three stages that require different temporal resolutions to describe them, these include: global expansion (∼3 ms), bulging (∼300 μs), and crack initiation and propagation (∼40 μs). The average strain rate in the global expansion is estimated to be around 100 microstrain/μs. The strain rates of bulging, crack initiation and crack propagation are difficult to determine with speckle pattern decorrelation. High-speed photography shows the crack first propagates along one direction, followed by opening in a perpendicular direction. The former has a velocity estimated at ∼0.73 Mach while the latter has an estimated opening velocity of ∼1.05 Mach. This study indicates the potential utility of high-speed DIC for the study of hearing mechanics, and highlights the need for the development of miniaturized imaging tools to perform high strain rate measurements in confined volumes.