Numerical study on dynamic mechanism of brain volume and shear deformation under blast loading

Blast-induced traumatic brain injury (b-TBI) is a kind of significant injury to soldiers in the current military conflicts. However, the mechanism of b-TBI has not been well understood, and even there are some contradictory conclusions. It is crucial to reveal the dynamic mechanism of brain volume and shear deformations under blast loading for better understanding of b-TBI. In this paper, the numerical simulation method is adopted to carry out comprehensive and in-depth researches on this issue for the first time. Based on the coupled Eulerian–Lagrangian method, the fluid–structure coupling model of the blast wave and human head is developed to simulate two situations, namely the head subjected to the frontal and lateral impacts. The simulation results are analyzed to obtain the underlying dynamic mechanisms of brain deformation. The brain volume deformation is dominated by the local bending vibration of the skull, and the corresponding frequency for the forehead skull under the frontal impact and the lateral skull faced to the lateral impact is as high as 8 kHz and 5 kHz, respectively. This leads to the high-frequency fluctuation of brain pressure and the large pressure gradient along the skull, totally different from the dynamic response of brain under head collisions. While the brain shear deformation mainly depends on the relative tangential displacement between the skull and brain and the anatomical structure of inner skull, being not related to the brain pressure and its gradient. By further comparing the medical statistics, it is inferred that diffuse axonal injury and brain contusion, the two most common types of b-TBI, are mainly attributed to brain shear deformations. And the von Mises stress can be adopted as the indicator for these two brain injuries. This study can provide theoretical guidance for the diagnosis of b-TBI and the development of protective equipment.