Traumatic Brain Injury (TBI) is a significant public health and financial concern that is affecting tens of thousands of people in the United States annually. There were over a million hospital visits related to TBI in 2017. Along with immediate and short-term morbidity from TBI, chronic traumatic encephalopathy (CTE) can have life-altering, chronic morbidity, yet the direct linkage of how head impacts lead to this pathology remains unknown. A possible clue is that chronic traumatic encephalopathy appears to initiate in the depths of the sulci. The purpose of this study was to isolate the injury mechanism/s associated with blunt force impact events. To this end, drop tower experiments were performed on a human head phantom. Our phantom was fabricated into a three-dimensional extruded ellipsoid geometry made out of Polyacrylamide gelatin that incorporated gyri-sulci interaction. The phantom was assembled into a polylactic acid 3D-printed skull, surrounded with deionized water, and enclosed between two optical windows. The phantom received repetitive low-force impacts on the order of magnitude of an average boxing punch. Intracranial pressure profiles were recorded in conjunction with high-speed imaging, 25 k frames-per-second. Cavitation was observed in all trials. Cavitation is the spontaneous formation of vapor bubbles in the liquid phase resulting from a pressure drop that reaches the vapor pressure of the liquid. The observed cavitation was predominately located in the contrecoup during negative pressure phases of local intracranial pressure. To further investigate the cavitation interaction with the brain tissue phantom, a 2D plane strain computational model was built to simulate the deformation of gyrated tissue as a result from the initiation of cavitation bubbles seen in the phantom experiments. These computational experiments demonstrated a focusing of strain at the depths of the sulci from bubble expansion. Our results add further evidence that mechanical interactions could contribute to the development of chronic traumatic encephalopathy and also that fluid cavitation may play a role in this interaction.

This study shows the basic design and experimental characterization of the advanced blast chamber at Michigan State University. This facility is a large cross-section explosively-driven blast chamber. The cross-section of the facility is 2.03 m × 2.03 m, and the length of its tunnel is 5.5 m. This relatively short length was made possible by introducing a new driver design shaped like a pair of logarithmic spirals with a coincident focus. The experimental characterization of the facility demonstrates that this driver design produces blast fronts with very low curvature, and overpressure durations as short as ∼1.2 ms. Since this was the initial characterization of the facility, the maximum overpressure considered was ∼144 kPa. This facility was conceived to perform studies of blast-induced traumatic brain injury based on full-size models of the human body or large animal models. Its large cross section ensures that area blockage is within permissible values, and its driver design ensures short overpressure durations typical of battle field blast events.

A well known result from the non-linear theory of elasticity applied to spherical shells is that the classical Mooney-Rivlin constitutive law may give either a monotonic or a nonmonotonic pressure-inflation response for finite deformation. Specifically, this is determined by two factors: the relative shell thickness, and the relative I 1 to I 2 contribution in the M-R constitutive law. Here we consider how a residual stress field may affect this behavior. Using a constitutive framework for hyperelastic materials with residual stress that has been especially applied to tubes, this paper focuses on finite thickness spherical shells while using a similar prototypical energy response. In this context we examine different residual stress states, and show how certain of these lead to more workable analytical results than others. All of them enable Taylor and asymptotic expansions in the small and large inflation limit. On this basis it is shown how particular residual stress fields can cause a monotonic inflation graph to become non-monotonic, and vice versa.

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In the context of the extensively studied problem for finite amplitude radial motion of incompressible isotropic hyperelastic cylinders, we consider the effect of material property discontinuity on the response of finite thickness multilayer tubes. This enables explicit characterization of the effect of layer differences (density mismatch, constitutive parameter mismatch (e.g. shear moduli), and interface location). Example demonstration is given in terms of the phase-plane treatment for free oscillation of a two-layer Mooney-Rivlin tube. Equivalent results are then obtained by a fully independent energy treatment which proceeds with no mention of the concept of stress. The second order equation of motion emerges both by a Lagrangian treatment and also by Hamilton's principle.