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Solid-beam finite element analysis of Nitinol stents

机译：镍钛诺支架的固体束有限元分析

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This paper discusses the finite element (FE) modelling of Nitinol stent structures by means of a recently introduced solid-beam finite element technology. FE stenting simulations based on standard 3D solid elements are computationally very expensive. An adequate FE discretization of the stent structure requires a large number of elements for two reasons: Several elements are needed in the thickness directions of the stent struts in order to resolve localized martensite transformations. Additionally, due to the slenderness of the struts, a dense discretization in longitudinal direction is required to retain reasonable element aspect ratios. In combination with non-linearities emerging from the non-linear material behaviour, large deformations, and contact, stenting simulations become very challenging and time consuming. The solid-beam finite element technology is considered to reduce computational costs by working with only one element in thickness direction and allowing larger aspect ratios while the results are still acceptable to be used in the iterative design process. The here suggested formulation based on an eight-node brick element geometry is suitable to efficiently model beam-like structures with prismatic cross-sections without the necessity of abstracting the beam axes from the three-dimensional (3D) geometry. All relevant locking phenomena are alleviated by a tailored combination of different techniques. The combination of the new finite element technology with a sophisticated material model that represents the pseudoelastic behaviour of Nitinol is an additional aspect to be investigated in this regard. Validations at the example of an isolated strut show that very accurate results are obtained for thick and thin strut geometries. Moreover, we successfully simulate the crimping-expanding process of an intracranial stent showing a very complex geometry. The results match those based on high density solid meshes very well. The computational benefit becomes clearly evident. (C) 2015 Elsevier B.V. All rights reserved.
机译：本文讨论了镍钛合金支架结构的有限元（FE）建模，这是通过最近引入的固体束有限元技术实现的。基于标准3D实体元素的FE支架仿真在计算上非常昂贵。支架结构的适当FE离散化需要大量元素，这有两个原因：在支架支杆的厚度方向上需要几个元素，以解决局部马氏体转变。另外，由于支柱的细长性，需要在纵向上进行密集的离散化以保持合理的单元长宽比。与非线性材料行为，大变形和接触引起的非线性相结合，支架模拟变得非常具有挑战性且耗时。通过在厚度方向上仅使用一个元素并允许更大的宽高比，而将结果仍然可以用于迭代设计过程中，则认为固体束有限元技术可以降低计算成本。此处建议的基于八节点砖元素几何结构的公式适合于有效地建模具有棱柱形横截面的梁状结构，而无需从三维（3D）几何图形中抽象出梁轴。通过不同技术的量身定制，可以减轻所有相关的锁定现象。新的有限元技术与代表镍钛诺的拟弹性行为的复杂材料模型的结合是在这方面要研究的另一个方面。在单独的支撑杆示例中进行的验证表明，对于厚和薄的支撑杆几何结构都可以获得非常准确的结果。此外，我们成功地模拟了显示非常复杂的几何形状的颅内支架的压接扩展过程。结果与基于高密度实体网格的结果非常匹配。计算上的好处变得显而易见。 （C）2015 Elsevier B.V.保留所有权利。

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