Brain Tissue Mechanical Characterization and Determination of Brain Response under Confined Blasts Explosions

Mechanical experimental tests including stress relaxation, simple monotonic ramps, and impact loads were performed on porcine brain tissues to investigate the response of the brain under different loading scenarios. Linear viscoelastic models were employed to determine the applicability and limitations of the linear mechanical models in tension. In addition the lowest and highest stress values, which can be possibly applied to the tissue due to change in the strain rates, were investigated using stress relaxation experiments to implicitly address the two levels of strain rates. Porcine brainstem samples were tested in six stress relaxation experimental settings at strain amplitudes ranging from 5% to 30% in compression. The lowest stress was directly measured from long-term responses of stress relaxation experiments when the stress values remained constant. The highest stress level was determined by using the quasi-linear viscoelasticity theory and estimating the instantaneous stress of the samples at six strain amplitudes. It was hypothesized that there is a correlation between the two pure elastic behaviors. The hypothesis was true as a strong linear correlation was found between the two elastic responses. The results showed that the instantaneous stress values were 11 times greater than the long-term stress values, practically similar across all strain amplitudes. In the second part of the thesis, a number of computational studies were conducted using a validated human head model. The head model included major components of human head and underwent different blast scenarios in open and confined spaces. The study investigated the effect of reflections from the walls. The results show that when the head was in the vicinity of the wall, the biomechanical parameters were dramatically increased, especially in the corners. Comparing brain biomechanical parameters in confined, semi-confined, and open spaces under blast loads, the brain sustained greater stress and strain values, with larger duration of the loads, in confined spaces. Also, a primary blast injury (PBI) with a tertiary blast injury (TeBI) in a confined space was compared. The results indicated that the PBI due to the incident shock wave was much more injurious than TeBI due to blunt impact.Department of Defens