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Is the 0.2%-Strain-Offset Approach Appropriate for Calculating the Yield Stress of Cortical Bone?
Annals of Biomedical Engineering ( IF 3.8 ) Pub Date : 2021-01-21 , DOI: 10.1007/s10439-020-02719-2
Guanjun Zhang 1 , Junjie Luo 1 , Gang Zheng 1 , Zhonghao Bai 1 , Libo Cao 1 , Haojie Mao 2
Affiliation  

The 0.2% strain offset approach is mostly used to calculate the yield stress and serves as an efficient method for cross-lab comparisons of measured material properties. However, it is difficult to accurately determine the yield of the bone. Especially when computational models require accurate material parameters, clarification of the yield point is needed. We tested 24 cortical specimens harvested from six bovine femora in three-point bending mode, and 11 bovine femoral cortical specimens in the tensile mode. The Young’s modulus and yield stress for each specimen derived from the specimen-specific finite element (FE) optimization method was regarded as the most ideal constitutive parameter. Then, the strain offset optimization method was used to find the strain offset closest to the ideal yield stress for the 24 specimens. The results showed that the 0 strain offsets underestimated (− 25%) the yield stress in bending and tensile tests, while the 0.2% strain offsets overestimated the yield stress (+ 65%) in three-point bending tests. Instead, the yield stress determined by 0.007 and 0.05% strain offset for bending and tensile loading respectively, can effectively characterize the biomechanical responses of the bone, thereby helping to build an accurate FE model.



中文翻译:

0.2% 应变偏移法是否适用于计算皮质骨的屈服应力?

0.2% 应变偏移方法主要用于计算屈服应力,并作为跨实验室比较测量材料特性的有效方法。然而,很难准确地确定骨头的产量。特别是当计算模型需要准确的材料参数时,需要澄清屈服点。我们以三点弯曲模式测试了从 6 个牛股骨中采集的 24 个皮质标本,并以拉伸模式测试了 11 个牛股骨皮质标本。由特定于试样的有限元 (FE) 优化方法得出的每个试样的杨氏模量和屈服应力被认为是最理想的本构参数。然后,采用应变偏移优化方法为 24 个试件找到最接近理想屈服应力的应变偏移。结果表明,在弯曲和拉伸试验中,0 应变偏移低估了 (- 25%) 屈服应力,而 0.2% 应变偏移高估了三点弯曲试验中的屈服应力 (+ 65%)。相反,分别由弯曲和拉伸载荷的 0.007% 和 0.05% 应变偏移确定的屈服应力可以有效地表征骨骼的生物力学响应,从而有助于建立准确的 FE 模型。

更新日期:2021-01-22
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