Shock wave interaction with a fluid filled cylinder experimental methods

In the recent wars of Iraq and Afghanistan, many soldiers sustained bTBI (blast-induced traumatic brain injury). The blasts are created by extensive use of improvised explosive devices (IED’s). Whether pure blast-shock waves cause TBI or what is the mechanism of injury are not fully known. Research efforts are underway to find answers to these questions. The primary objective of this project is to understand how the shockwave interacts with a fluid-filled cylinder of different thicknesses. Here, the cylinder is idealized as head and the fluid filled inside it as the brain material. The primary interest here is, how the pure shockwave behaves when a cylinder is exposed to different incident blast over-pressures. The question raised in this work is whether primary blast wave causes for TBI? The pressure response inside the cylinder and the deformations for different thicknesses exposing at different blast loadings are taken into account in answering this question. Polycarbonate is chosen to simulate human skull. De-ionized water is used as the fluid as its mechanical property is close to that of brain. As the human head varies in thickness from 4mm in the temporal region to 8mm in the occipital region of the skull, two different thickness polycarbonate cylinders have been used to mimic that variation. All the experiments are done in the blast tube where the shockwaves are produced in the test section. Pure shock wave due to explosives in free field conditions will have a Friedlander wave form which will be artificially generated in 9 inch shock tube. High speed cameras are used for capturing motion of the cylinder during shock loading. Two different pressures 20 psi (140 kPa) and 30 psi (210 kPa) are used as the peak blast overpressures with two different thickness 1.9 and 3.3mm and diameter of the cylinder is 50mm. Pressure in the fluid is measured at three different locations whereas strain gages measure deformations at three sites. Analysis of data indicate that the pressure in the fluid is affected by not only the external pressure but also thickness of the cylinder. Thus, the pressure is affected by both direct transmission as well as cylinder deformation