Strain. 2020;56:e12331. https://doi.org/10.1111/str.12331 Abstract Biaxial tests are commonly used to investigate the mechanical behaviour of anisotropic soft biological tissues such as cardiovascular tissues. However, there is still no clear understanding of the influence that the biaxial test set‐ up conditions may have on the computing material stress of the experimental results. The aim of the present study is to further investigate the accuracy of calculated material stress from measured force during biaxial tests using finite element methods (FEM). The biaxial mechanical response of ascending aorta and pulmonary artery tissue samples was obtained by FEM simulation under two different gripping methods: (a) a system with noodle clamps and (b) a clamped system with needles which leave the specimen's edges free to expand laterally. The results show that the clamped method whose joints allow free movement in the lateral direction produces stresses closer to the universally accepted formulation of biaxial material stress in the central region. However, the system with noodle clamps, commonly used to grip the sample, produces an alteration of the measurement stresses. Our simulations show results giving an inaccurate estimation of the stress at the centre of the sample. In some cases, the stresses are overestimated and in others underestimated depending on the anisotropy of the sample. We can conclude that the clamped system with needles which leave the specimen's edges free to expand laterally should be used as an efficient methodology to other commonly used gripping methods for biological tissues with anisotropic materials.

中文翻译：

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动脉双轴试验标称应力计算精度分析

拉紧。2020；56：e12331。https://doi.org/10.1111/str.12331 摘要 双轴试验常用于研究心血管组织等各向异性软生物组织的力学行为。然而，对于双轴试验设置条件可能对计算实验结果的材料应力的影响，仍然没有明确的认识。本研究的目的是进一步研究使用有限元方法 (FEM) 进行双轴试验时根据测得的力计算出的材料应力的准确性。升主动脉和肺动脉组织样本的双轴机械响应是通过 FEM 模拟在两种不同的夹持方法下获得的：（a）带有面条夹的系统和（b）带有针的夹持系统，使样本的边缘可以自由横向扩展。结果表明，接头允许横向自由移动的夹紧方法产生的应力更接近于中心区域普遍接受的双轴材料应力公式。然而，通常用于夹住样品的带有面条夹的系统会改变测量应力。我们的模拟显示结果给出了对样品中心应力的不准确估计。在某些情况下，根据样品的各向异性，应力被高估，而在其他情况下则被低估。我们可以得出结论，带有针头的夹紧系统可以使标本的边缘自由横向扩展，应该用作其他常用的具有各向异性材料的生物组织夹持方法的有效方法。