Model parameters for the studied material.

With the development of medical diagnosis and treatment, knowing the mechanical properties of living tissues becomes critical. The aim of this study was to investigation material properties of the fresh porcine kidney and the parametric characterization of its viscoelastic material behavior. The material investigation included uniaxial tension tests in different strain rates, relaxation tests, as well as hydrostatic compression tests on the samples extracted from the fresh porcine kidney cortex. Tension tests and relaxation tests were performed by a planar dog-bone specimen with a micron loading testing machine. Hydrostatic compression tests were performed on the kidney cylinder sample which was placed in a compression chamber. Furthermore, a nonlinear viscoelastic model recently proposed by us was employed to characterize the tension data at different strain rates and relaxation test data. The the experimental and numerical results show that the stress-strain relations of the porcine kidney cortex at different strain rates in tension are presented for the first time and a higher strain rate results in higher ultimate strength and initial Young modulus but a lower rupture strain. A damage-dependent visco-elastic model is employed to model the tension data at different strain rates and relaxation data and exhibits a good agreement with the experimental data, which also demonstrates that the damage has an obvious influence on the stress-strain relation. Through comparison with the existing reference covering the uniaxial compression data, it seems that the mechanical behavior of the porcine kidney cortex manifests a stress state-dependent mechanical behavior. The ultimate strength and rupture strain are larger in compression than that in tension.

随着医疗诊疗技术的发展，获取活体组织的力学特性已成为至关重要的研究方向。本研究旨在探究新鲜猪肾的材料特性，并对其粘弹性（viscoelastic）材料行为进行参数化表征。本次材料表征实验涵盖了从新鲜猪肾皮质提取的样本的不同应变速率单轴拉伸试验、松弛试验，以及静水压压缩试验。拉伸试验与松弛试验采用平面狗骨形试样，通过微米级加载试验机完成；静水压压缩试验则针对置于压缩腔中的肾圆柱试样开展。此外，本研究采用课题组近期提出的非线性粘弹性（nonlinear viscoelastic）模型，对不同应变速率下的拉伸数据与松弛试验数据进行表征。实验与数值结果表明，本研究首次报道了猪肾皮质在不同应变速率下的拉伸应力-应变关系：更高的应变速率会带来更高的极限强度与初始杨氏（Young）模量，但断裂应变更低。本研究所采用的考虑损伤的粘弹性模型可对不同应变速率下的拉伸数据与松弛数据进行拟合，且与实验数据吻合度良好，同时证实了损伤对猪肾皮质的应力-应变关系具有显著影响。通过与已发表的涵盖单轴压缩数据的相关文献对比可知，猪肾皮质的力学行为表现出应力状态依赖性：其压缩状态下的极限强度与断裂应变均大于拉伸状态下的对应值。