RESEARCH ON DYNAMIC MECHANICAL RESPONSE AND CONSTITUTIVE MODEL OF PORCINE LIVER

Impact-induced injuries to the abdominal organs appear frequently in traffic accidents and even cause serious life-threatening. The liver is one of the most vulnerable abdominal organs, leading to high mortality rate. An understanding of the dynamic mechanical behaviors of the liver could aid in the design of the safety equipment to effectively reduce the occurrence of liver injury. The specimens of liver parenchyma were harvested from the fresh porcine livers. The Instron material testing machine was used to obtain the quasi-static responses up to the point of failure at the two strain rates (0.004 s^-1 and 0.04 s^-1) and two loading directions (perpendicular and parallel directions to the liver surface). The high strain rate (1 300 s^-1, 2 400 s^-1, 4 500 s^-1) experiments were performed using the modified SHPB equipment along the liver surface. The results show that all stress-strain curves are nonlinear and concave upward. Stress level of curves is very low at the initial stage up to about 30% strain, and then increases steeply. No significant differences in the failure stress (about 0.45 MPa) and strain (about 48%) were observed for two loading rates and directions at quasi-static tests. However, it was found that the liver tissue became much stiffer at high strain rates than at quasi-static rates, indicating the strain rate dependence. The Yeoh hyperelastic material model was used to characterize the mechanical behaviors of the liver at quasi-static loading. Based on an improved visco-hyperelastic model, a rate-dependent constitutive model was proposed to describe the responses of the liver from the low strain rates to high strain rates. The model is found to be in excellent agreement with the experimental results.