Abstract
Understanding and modeling the mechanical behaviors of white matter brain tissue is important to gain insights into brain injury. With embedded axonal fiber bundles, white matter is typically treated as an anisotropic material whose mechanical behaviors and properties are extensively studied and characterized through experimental approaches in the past decades. However, although the injured brain tissue may experience large deformation in some head impact scenarios, most works characterize the white matter in a small-strain regime to avoid the large deformation-induced damage. Both experimental and modeling studies of white matter at large strain are still few, especially when the damage effect is included. We recently performed the indentation tests on porcine white matter with the indenter having a large displacement and found a clear damage initiation and progressive failure behavior of white matter when deformed beyond certain strain levels. To model this behavior, we assume that this failure phenomenon is caused by the fracture of axonal fiber bundles and propose a coupled hyperelasticity-damage constitutive model. The proposed constitutive model is implemented into finite element codes that is used to reproduce the indentation process. Results show that by using this proposed constitutive model with identified parameters, the finite element simulation can reproduce the damage initiation observed in experiments.
