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Modeling the durability of structural components in aerospace and medical industries.

机译：对航空航天和医疗行业中结构部件的耐久性进行建模。

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摘要

This dissertation presents applications of the finite element method in studying the durability of components used in aerospace (composites) and medical (hip implants) industries. In the first part of the dissertation the response of a fiber-reinforced composite material, subjected to loads that activate a number of micromechanisms of failure, is investigated in details. A composite material is heterogeneous in nature and generally exhibits local failures before final catastrophic failure at the structural level. The failure mechanisms in this class of materials generally span a number of length scales. Thus, local failure occurs at the micro-level in the form of fiber fracture, fiber buckling, matrix cracking, fiber-matrix debonding, and radial cracks at fiber-matrix interface. At the laminate level, failure occurs in the form of (i) intralaminar cracks in planes parallel and perpendicular to the fiber direction, and (ii) interlaminar cracks between two plies of a laminate; the latter resulting in delamina- tion of the plies. A number of experimental studies aimed at understanding the failure mechanisms under different loading conditions have been reported in the literature. Simultaneously, various analytical and numerical models have also been developed to predict the different failure mechanisms. Such models match experimental data to varying degrees of accuracy. It is generally very difficult to consider all the different failure mechanisms that are observed in experiments, in a single numerical model. This area of research is still in progress. In this study, we focus on simultaneously capturing two major modes of failure that occur in fiber reinforced composites subjected to tensile loading. These are the splitting (intralaminar) and the delamination (interlaminar) modes of failure, respectively. Experimental observations suggest that these failure mechanisms typically occur in conjunction. The objective of this study is to model these experimental observations using tools available in the commercial finite element code, ABAQUS. Two different failure criteria, following the work by Hashin and Linde, respectively, are utilized to predict the intralaminar failure mechanisms. The interlaminar failure mechanisms, on the other hand, are modeled using cohesive elements that are based on a traction-separation law used to characterize the constitutive response of the interfaces between the plies. The predictions based on the numerical simulations are compared to experiments and other available data from the literature, and provide useful insights towards the combined modeling of the above-mentioned failure modes.;In the second part of this dissertation an artificial hip implant is investigated from a durability point of view. The advent of artificial hip implants has restored mobility to a lot of patients in recent years, and total hip replacement surgeries are being performed routinely over the past few decades. In 2005 approximately 208,600 surgeries were performed and it is estimated to increase by approximately 174% by 2030. Given such a trend, it is important to ensure that the implant performs as flawlessly as possible, and as closely as possible to the real hip joint. This has led to studies seeking a detailed understanding of the mechanistic and biological aspects of hip implants. In this work, we develop a finite element model of the implant including the femoral ball, and analyze its mechanical response under a single stance phase of gait. The long term durability is investigated based on the computed stresses. In addition, the responses of two-dimensional models are compared to that of a corresponding three-dimensional model, with the aim of determining the applicability of simpler two-dimensional models towards making accurate predictions of the stress and deformation states in the implant. Some other aspects that are also investigated include: (i) the variations of the stress distribution in the implant with femoral ball size, (ii) the nature of the contact interactions between the femoral ball and the implant, and (iii) the influence of the details of the loading and the boundary conditions on the response of the implant. An analytical model is developed to validate the results from the two-dimensional model. The results suggest that the stresses in the neck region of the femoral stem are higher when a smaller sized femoral ball is used. However, the stresses in the region of contact between the ball and the stem appear to be higher for a larger sized femoral ball.
机译：本文提出了有限元方法在研究航空航天（复合材料）和医疗（髋关节植入物）行业所用部件的耐久性方面的应用。在论文的第一部分中，对纤维增强复合材料的响应进行了详细的研究，该复合材料承受了激活许多破坏微观机制的载荷。复合材料本质上是异质的，通常在结构级别的最终灾难性破坏之前表现出局部破坏。这类材料的失效机制通常跨越许多长度尺度。因此，局部失效在微观层面上以纤维断裂，纤维屈曲，基体破裂，纤维-基质剥离和纤维-基质界面处的径向裂纹的形式发生。在层压制品的水平上，失效的形式为：（i）在平行于和垂直于纤维方向的平面中的层内裂缝，和（ii）层压制品的两层之间的层间裂缝；后者导致板层分层。文献中已经报道了许多旨在了解不同载荷条件下的破坏机理的实验研究。同时，还开发了各种分析和数值模型来预测不同的失效机理。这样的模型将实验数据匹配到不同程度的准确性。通常很难在单个数值模型中考虑实验中观察到的所有不同故障机制。该研究领域仍在进行中。在这项研究中，我们专注于同时捕获在承受拉伸载荷的纤维增强复合材料中发生的两种主要破坏模式。这分别是分裂（腹腔内）和分层（层间）失败模式。实验观察表明，这些故障机制通常同时发生。这项研究的目的是使用商业有限元代码ABAQUS中可用的工具对这些实验观察进行建模。分别遵循Hashin和Linde的工作，使用两种不同的失效准则来预测层内失效机理。另一方面，层间破坏机制是使用内聚元素建模的，该内聚元素基于用于描述层之间界面本构响应的牵引分离定律。将基于数值模拟的预测结果与实验和文献中的其他可用数据进行比较，并为上述失效模式的组合建模提供有用的见识。耐久性的观点。近年来，人工髋关节植入物的出现使许多患者恢复了活动能力，并且在过去的几十年中，常规进行了全部髋关节置换手术。 2005年，进行了约208,600例外科手术，估计到2030年将增长约174％。鉴于这种趋势，重要的是要确保植入物表现得尽可能完美，并尽可能接近真实的髋关节。这导致了研究寻求对髋关节植入物的机械和生物学方面的详细了解。在这项工作中，我们开发了包括股骨球在内的植入物的有限元模型，并分析了在步态单步态下的机械反应。根据计算得出的应力研究长期耐久性。另外，将二维模型的响应与相应的三维模型的响应进行比较，目的是确定更简单的二维模型在准确预测植入物中应力和变形状态方面的适用性。还研究了其他一些方面，包括：（i）植入物中应力分布随股骨球大小的变化；（ii）股骨球与植入物之间的接触相互作用的性质，以及（iii）负载的详细信息以及植入物响应的边界条件。开发了一个分析模型以验证二维模型的结果。结果表明，当使用较小尺寸的股骨球时，股骨柄颈部区域的应力较高。然而，对于较大尺寸的股骨球，在球与杆之间的接触区域中的应力似乎更高。

著录项

  • 作者

    Shaik, Sameer.;

  • 作者单位

    The University of North Carolina at Charlotte.;

  • 授予单位 The University of North Carolina at Charlotte.;
  • 学科 Engineering Biomedical.;Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 176 p.
  • 总页数 176
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 生物医学工程;机械、仪表工业;
  • 关键词

  • 入库时间 2022-08-17 11:38:24

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