Amstutz Cornelia, Weisse Bernhard, Haeberlin Andreas, Burger Jürgen, Zurbuchen Adrian
School of Biomedical and Precision Engineering, University of Bern, 3008 Bern, Switzerland.
EMPA, Swiss Federal Laboratories for Material Science and Technology, Mechanical Systems Engineering, 8600 Duebendorf, Switzerland.
Polymers (Basel). 2022 Aug 25;14(17):3476. doi: 10.3390/polym14173476.
Finite-element (FE) simulations that go beyond the linear elastic limit of materials can aid the development of polymeric products such as stretch blow molded angioplasty balloons. The FE model requires the input of an appropriate elastoplastic material model. Up to the onset of necking, the identification of the hardening curve is well established. Subsequently, additional information such as the cross-section and the triaxial stress state inside the specimen is required. The present study aims to inversely identify the post-necking hardening behavior of the semi-crystalline polymer polyamide 12 (PA12) at different temperatures. Our approach uses structural FE simulations of a dog-bone tensile specimen in LS-DYNA with mesh sizes of 1 mm and 2 mm, respectively. The FE simulations are coupled with an optimization routine defined in LS-OPT to identify material properties matching the experimental behavior. A Von Mises yield criterion coupled with a user-defined hardening curve (HC) were considered. Up to the beginning of necking, the Hockett−Sherby hardening law achieved the best fit to the experimental HC. To fit the entire HC until fracture, an extension of the Hockett−Sherby law with power-law functions achieved an excellent fit. Comparing the simulation and the experiment, the following coefficient of determination R2 could be achieved: Group I: R2 > 0.9743; Group II: R2 > 0.9653; Group III: R2 > 0.9927. Using an inverse approach, we were able to determine the deformation behavior of PA12 under uniaxial tension for different temperatures and mathematically describe the HC.
超越材料线性弹性极限的有限元（FE）模拟有助于拉伸吹塑血管成形术球囊等聚合物产品的开发。有限元模型需要输入合适的弹塑性材料模型。在颈缩开始之前，硬化曲线的识别已经很成熟。随后，还需要诸如试样内部的横截面和三轴应力状态等额外信息。本研究旨在反向识别半结晶聚合物聚酰胺12（PA12）在不同温度下的颈缩后硬化行为。我们的方法使用了LS-DYNA中狗骨拉伸试样的结构有限元模拟，网格尺寸分别为1毫米和2毫米。有限元模拟与LS-OPT中定义的优化程序相结合，以识别与实验行为匹配的材料特性。考虑了与用户定义的硬化曲线（HC）相结合的冯·米塞斯屈服准则。在颈缩开始之前，霍克特-谢尔比硬化定律与实验硬化曲线拟合得最好。为了拟合直至断裂的整个硬化曲线，用幂律函数扩展霍克特-谢尔比定律实现了极佳的拟合。比较模拟和实验结果，可得到以下决定系数R2：第一组：R2>0.9743；第二组：R2>0.9653；第三组：R2>0.9927。使用反向方法，我们能够确定PA12在不同温度下单轴拉伸下的变形行为，并从数学上描述硬化曲线。
