Traumatic brain injuries (TBI) affect millions of people each year. While research has been dedicated to determining the mechanical properties of the uninjured brain, there has been a lack of investigation on the mechanical properties of the brain after experiencing a primary blast-induced TBI. In this paper, whole porcine brains were exposed to a shock wave to simulate blast-induced TBI. First, ten (10) brains were subjected to unconfined compression experiments immediately following shock wave exposure. In addition, 22 brains exposed to a shock wave were placed in saline solution and refrigerated between 30 minutes and 6.0 hours before undergoing unconfined compression experiments. This study aimed to investigate the effect of a time delay on the viscoelastic properties in the event that an experiment cannot be completed immediately. Samples from both soaked and freshly extracted brains were subjected to compressive rates of 5, 50, and 500 mm/min during the unconfined compression experiments. The fractional Zener (FZ) viscoelastic model was applied to obtain the brain's material properties. The length of time in the solution statistically influenced three of the four FZ coefficients, E 0 (instantaneous elastic response), τ 0 (relaxation time), and α (fractional order). Further, the compressive rate statistically influenced τ 0 and α.
AbstractTraumatic brain injuries (TBI) affect millions of people each year. While research has been dedicated to determining the mechanical properties of the uninjured brain, there has been a lack of investigation on the mechanical properties of the brain after experiencing a primary blast-induced TBI. In this paper, whole porcine brains were exposed to a shock wave to simulate blast-induced TBI. First, ten (10) brains were subjected to unconfined compression experiments immediately following shock wave exposure. In addition, 22 brains exposed to a shock wave were placed in saline solution and refrigerated between 30 minutes and 6.0 hours before undergoing unconfined compression experiments. This study aimed to investigate the effect of a time delay on the viscoelastic properties in the event that an experiment cannot be completed immediately. Samples from both soaked and freshly extracted brains were subjected to compressive rates of 5, 50, and 500 mm/min during the unconfined compression experiments. The fractional Zener (FZ) viscoelastic model was applied to obtain the brain's material properties. The length of time in the solution statistically influenced three of the four FZ coefficients, E 0 (instantaneous elastic response), τ 0 (relaxation time), and α (fractional order). Further, the compressive rate statistically influenced τ 0 and α.
Traumatic brain injuries (TBI) affect millions of people each year and can result in long-term difficulties in thinking or focusing. Due to the number of people affected by these injuries, significant research has been dedicated to determining the mechanical properties of the brain using postmortem tissue from animals harvested within 24 hours. The postmortem brain tissue is often stored in a solution until a rheological experiment is ready to begin. However, the effect of storage duration on the mechanical behavior of brain tissue is not understood. In this paper, postmortem porcine brains were placed in normal saline solution (0.9% NaCl) and refrigerated between 30 minutes and 6.5 hours to allow the brain to absorb the solution. Afterwards, samples from both soaked and freshly extracted brains were subjected to unconfined compression tests at compressive rates of 5, 50, and 500 mm/min. The fractional Zener viscoelastic model was applied to obtain the brain's mechanical properties. While the results did not show a significant relationship between absorption and the long-term stiffness (E ∞ ), both the relaxation time (τ 0 ) and fractional order (α) were statistically influenced by both the length of time in the solution and compressive rate. Further, the instantaneous stiffness (E 0 ) was statistically influenced by the length of time in solution, though not the compressive rate.
To address the negative contribution of cement production on global carbon emissions, this study aims to reduce the cement content typically required in concrete using partial replacement by gypsum powder recycled from waste drywalls (15%) and fly ash (50%), by weight. The durability of concrete cylinders made of the mixture was evaluated by testing the cylinders in compression after exposure to various environmental conditions for 1000-, 3000- and 5000 hours. A total of 45 specimens under five exposure conditions were considered. The conditions included: dry, submerged in fresh water, submerged in seawater, and two groups rotated weekly between dry and submerged in either fresh water or seawater. Overall, specimens in both freshwater and seawater conditions after 5000 hrs showed strength higher than control specimens. Results indicate that the strength of the concrete specimens containing recycled gypsum powder and fly ash was not adversely affected by exposure to the conditions.
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