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Surface damage of metallic implants due to mechanical loading and chemical reactions.

机译：由于机械负载和化学反应，金属植入物的表面损坏。

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摘要

The present study investigates interfacial damage mechanism of modular implants due to synergetic action of mechanical contact loading and corrosion. Modular implants are manufactured such that surfaces have a characteristic degree of roughness determined by tool tip size and motion of tool path or feeding speed. The central hypothesis for this work is that during contact loading of metallic implants, mechanisms of damage and dissolution are determined by contact loads, plastic deformation, residual stresses and environmental conditions at the nanoscale surface asperities; while during subsequent rest periods, mechanism of metallic dissolution is determined by the environmental conditions and residual stress field induced due to long range elastic interactions of the plastically deformed asperities. First part of the thesis is focused on investigating the mechanisms underlying surface roughness evolution due to stress-assisted dissolution during the rest period. The latter part is focused on investigating material removal mechanisms during single asperity contact of implant surfaces.;Experimental study was performed to elucidate the roughness evolution mechanism by combined effect of multi-asperity contact and environmental corrosion. Cobalt-chromium-molybdenum specimen was subjected to either contact loading alone or alternating contact loading and exposure to reactive environment. Roughness of the specimen surface was monitored by optical profilometry and Fast Fourier Transform (FFT) calculation was used to characterize the evolving behavior of roughness modes. Finite element analysis (FEA) was employed to identify influences of surface morphological configurations and contact pressures on the residual stress development. Analytical model of multi-asperity contact has been developed for prediction of residual stress field for different roughness configurations during varying magnitude of contact loads based on elastic inclusion theory. Experimental results indicate that surface roughness undergoes continuous evolution during alternating contact loading and exposure to etchant. Surface roughness evolution is governed by the residual stress induced due to contact loading. Two different stress-assisted dissolution driven instabilities in roughness evolution have been identified.;In order to investigate stressed surface damage by electrochemical reaction during active contact loading, in the first stage, surface failure due to sliding contact was investigated as a function of different residual stress states from compressive to tensile. Residual stress is usually developed during manufacturing process or former mechanical interactions playing an important role on service life of the surface. The wear mechanism of fatigue contact in the presence of residual stresses was explored by analytical model of fatigue crack growth by utilizing modified delamination wear theory with surface layer spalling model. Fatigue stress intensity factors (DeltaKI) loaded by contact stress and combined residual stress implied that buckling of subsurface crack with compressive residual stress opens crack-tip and consequently increase wear rate during sliding contact. As for the experimental verification of the modified delamination model, cyclic sliding contact experiment on metallic implant materials in ambient was conducted by utilizing atomic force microscope (AFM) and four-point-bending set up by which well characterized pre-stress was established on rectangular specimen. In addition, complex mechanism of corrosion on the damaged surface illustrated strong stress-dependent effects on wear rate in repassivating environment and dissolution rates in reactive environment.
机译：本研究调查了由于机械接触载荷和腐蚀的协同作用而导致的模块化植入物的界面损伤机理。制造模块化植入物，使得表面具有特征粗糙度，该粗糙度由刀头尺寸和刀具路径或进给速度的运动确定。这项工作的中心假设是，在金属植入物的接触载荷过程中，损伤和溶解的机制取决于接触载荷，塑性变形，残余应力和纳米级表面凹凸不平的环境条件。而在随后的休息期间，金属溶解的机制取决于环境条件和塑性变形粗糙物的长距离弹性相互作用引起的残余应力场。本文的第一部分着重于研究在休息期间由于应力辅助溶解而引起的表面粗糙度演变的机理。后一部分主要研究植入物表面单次粗糙接触时的材料去除机理。；进行了实验研究，以阐明多粗糙接触与环境腐蚀相结合的粗糙度演变机理。钴-铬-钼样品单独经受接触载荷或交替接触载荷并暴露于反应性环境。通过光学轮廓仪监测样品表面的粗糙度，并使用快速傅里叶变换（FFT）计算来表征粗糙度模式的演变行为。有限元分析（FEA）被用来识别表面形态和接触压力对残余应力发展的影响。基于弹性夹杂理论，建立了多粗糙接触分析模型，用于预测不同粗糙度条件下不同接触载荷下残余应力场。实验结果表明，表面粗糙度在交替的接触载荷和暴露于蚀刻剂的过程中不断发生变化。表面粗糙度的演变受因接触载荷引起的残余应力支配。已经确定了两种不同的由应力辅助的，由溶解引起的不稳定性，它们在粗糙度变化中具有不稳定性。应力状态从压缩状态变为拉伸状态。残余应力通常在制造过程中产生，或者以前的机械相互作用在表面的使用寿命中起重要作用。利用修正的分层磨损理论和表面层剥落模型，通过疲劳裂纹扩展的解析模型，探讨了残余应力作用下疲劳接触的磨损机理。接触应力和残余残余应力共同作用的疲劳应力强度因子（DeltaKI）表示，地下裂纹与压缩残余应力的屈曲会打开裂纹尖端，从而增加滑动接触时的磨损率。关于改进脱层模型的实验验证，利用原子力显微镜（AFM）对金属植入材料在环境中进行了循环滑动接触实验，并建立了四点弯曲，从而在矩形上建立了特征良好的预应力。样品。此外，受损表面腐蚀的复杂机理表明，在钝化环境中，应力对磨损率和反应性环境中的溶解率具有很强的应力依赖性。

著录项

  • 作者

    Ryu, JaeJoong.;

  • 作者单位

    Iowa State University.;

  • 授予单位 Iowa State University.;
  • 学科 Engineering Biomedical.;Engineering Mechanical.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 133 p.
  • 总页数 133
  • 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;工程材料学;
  • 关键词

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