Abstract:
The rapid advancement in computational power has positioned human finite element (FE) models as highly efficient tools for biomechanically assessing the risk of abdominal injuries during crash events. This study focuses on a critical aspect of injury prediction: the characterization of human liver parenchyma under tensile loading, which is crucial for developing biofidelic human models for numerical impact simulations. To achieve this, specimen-specific FE models were developed and employed to quantitatively determine the material and failure properties of human liver parenchyma, leveraging a sophisticated FE optimization approach.
The experimental foundation of this biomechanical investigation involved uniaxial tensile tests performed on 34 parenchyma coupon specimens meticulously prepared from two fresh human livers. These specimens were subjected to failure at four distinct loading rates (0.01s −1 , 0.1s −1 , 1s −1 , and 10s −1 ), specifically to investigate the biomechanical effects of rate dependency on both the elastic and failure responses of the liver parenchyma. Each experimental test was then numerically simulated by precisely prescribing the end displacements of the corresponding specimen-specific FE models, directly correlating with the empirical test data.
For the constitutive characterization, parameters of a first-order Ogden material model were identified for each specimen using a rigorous FE optimization approach, particularly focusing on the pre-tear loading region of the liver tissue. Subsequently, mean material model parameters were precisely determined for each loading rate based on the characteristic averages of the stress-strain curves, with a stochastic optimization approach utilized to ascertain the standard deviations of these material model parameters. The study found that a hyperelastic material model, formulated with a tabulated representation for rate effects, demonstrated excellent predictive capabilities for the tensile material properties of human liver parenchyma.
Furthermore, to comprehensively capture the injury response, the critical process of tissue tearing was numerically simulated utilizing a cohesive zone modeling (CZM) approach. A layer of cohesive elements was strategically incorporated at the predicted failure location within the FE models, and the CZM parameters were meticulously identified by fitting the post-tear force-time history recorded during each experimental test. The significant results from this biomechanical modeling effort indicate that the proposed integrated approach is highly capable of capturing both the complex biomechanical response and the subsequent failure behavior of human liver parenchyma, thereby accurately modeling the overall force-deflection response across a wide spectrum of tensile loading rates. This methodology provides valuable data that can be readily implemented into existing human liver models, paving the way for a more accurate understanding of liver injury mechanisms in various impact scenarios.
