Background: The ring-pull test, where a ring of tissue is hooked via two pins and stretched, is a popular biomechanical test, especially for small arteries. Although convenient and reliable, the ring test produces inhomogeneous strain, making determination of material parameters non-trivial. Objective: To determine correction factors between ring-pull-estimated and true tissue properties. Methods: A finite-element model of ring pulling was constructed for a sample with nonlinear, anisotropic mechanical behavior typical of arteries. The pin force and sample cross-section were used to compute an apparent modulus at small and large strain, which were compared to the specified properties. The resulting corrections were validated with experiments on porcine and ovine arteries. The correction was further applied to experiments on mouse aortic rings to determine material and failure properties. Results: Calculating strain based on centerline stretch rather than inner-wall or outer-wall stretch afforded better estimation of tissue properties. Additional correction factors were developed based on ring wall thickness H, centerline ring radius Rc, and pin radius a. The corrected estimates for tissue properties were in good agreement with uniaxial stretch experiments. Conclusions: The computed corrections improved estimation of tissue material properties for both the small-strain (toe) modulus and the large-strain (lockout) modulus. When measuring tensile strength, one should minimize H/a to ensure that peak stress occurs at the sample midplane rather than near the pin. In this scenario, tensile strength can be estimated accurately by using inner-wall stretch at the midplane and the corrected properties.

中文翻译：

---

纤维软组织机械性能的环拉试验 - 单轴近似分析和非线性厚壁组织的校正


背景：拉环测试，即通过两个销钉钩住一圈组织并拉伸，是一种流行的生物力学测试，特别是对于小动脉。虽然方便可靠，但环形测试会产生不均匀的应变，使得材料参数的确定变得非常重要。目的：确定环拉力估计值与真实组织特性之间的校正因子。方法：针对具有典型动脉非线性、各向异性机械行为的样本构建了拉环的有限元模型。销钉力和样品横截面用于计算小应变和大应变下的表观模量，并将其与指定属性进行比较。由此产生的校正通过猪和羊动脉的实验得到验证。该校正进一步应用于小鼠主动脉环的实验，以确定材料和失效特性。结果：根据中心线拉伸而不是内壁或外壁拉伸计算应变可以更好地估计组织特性。根据环壁厚度 H、中心线环半径 Rc 和销半径 a 开发了附加修正系数。组织特性的校正估计与单轴拉伸实验非常一致。结论：计算出的校正改进了对小应变（脚趾）模量和大应变（锁定）模量的组织材料特性的估计。测量拉伸强度时，应最小化 H/a，以确保峰值应力出现在样品中平面而不是销附近。在这种情况下，可以通过使用中平面处的内壁拉伸和校正的属性来准确估计抗拉强度。