Brain's strain-rate-enhancement characteristic and a strong nonlinear viscoelastic model

Abstract

It is widely recognized that brain tissue exhibits a significant strain rate effect. However, due to technical limitations, the mechanical behavior of brain tissue within the strain rate range of 100–500 s⁻¹ remains poorly understood, leaving the accuracy of existing constitutive models for brain tissue inadequately validated. In this study, we employed a Long Split Hopkinson Pressure Bar (LSHPB) system designed for ultra-soft materials to characterize the mechanical behavior of brain tissue at strain rates of 125 s⁻¹ and 340 s⁻¹, thereby addressing the research gap concerning brain tissue behavior under intermediate strain rates. By integrating experimental data from low and high strain rate tests (0.001 s⁻¹, 0.1 s⁻¹, 700 s⁻¹, 900 s⁻¹, and 1700 s⁻¹, respectively), we further observed a significant shift in the strain rate enhancement effect within the intermediate strain rate range. This suggests that current rate-dependent constitutive models are insufficient to accurately describe the comprehensive rate-dependent mechanical behavior of brain tissue. Consequently, we developed a highly nonlinear viscoelastic model capable of effectively describing the mechanical behavior of brain tissue across low, intermediate, and high strain rate ranges. Our work accurately characterizes the large deformation behavior of brain tissue under intermediate strain rates for the first time, revealing its strong nonlinear strain rate enhancement characteristics. Additionally, a suitable constitutive model is proposed. This study not only provides comprehensive insights into the rate-dependent mechanical behaviors of brain tissue but also holds great potential for improving the accuracy of Finite Element Head Modeling (FEHM).