Ansari Farzana, Gludovatz Bernd, Kozak Adam, Ritchie Robert O, Pruitt Lisa A
Department of Mechanical Engineering, University of California, Berkeley, CA, USA.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
J Mech Behav Biomed Mater. 2016 Jul;60:267-279. doi: 10.1016/j.jmbbm.2016.02.014. Epub 2016 Feb 12.
Ultrahigh molecular weight polyethylene (UHMWPE) has remained the primary polymer used in hip, knee and shoulder replacements for over 50 years. Recent case studies have demonstrated that catastrophic fatigue fracture of the polymer can severely limit device lifetime and are often associated with stress concentration (notches) integrated into the design. This study evaluates the influence of notch geometry on the fatigue of three formulations of UHMWPE that are in use today. A linear-elastic fracture mechanics approach is adopted to evaluate crack propagation as a function of notch root radius, heat treatment and Vitamin E additions. Specifically, a modified stress-intensity factor that accounts for notch geometry was utilized to model the crack driving force. The degree of notch plasticity for each material/notch combination was further evaluated using finite element methods. Experimental evaluation of crack speed as a function of stress intensity was conducted under cyclic tensile loading, taking crack length and notch plasticity into consideration. Results demonstrated that crack propagation in UHMWPE emanating from a notch was primarily affected by microstructural influences (cross-linking) rather than differences in notch geometry.
超高分子量聚乙烯（UHMWPE）在髋关节、膝关节和肩关节置换手术中作为主要聚合物已使用了50多年。最近的案例研究表明，该聚合物的灾难性疲劳断裂会严重限制器械的使用寿命，并且通常与设计中集成的应力集中（缺口）有关。本研究评估了缺口几何形状对目前使用的三种UHMWPE配方疲劳性能的影响。采用线弹性断裂力学方法来评估裂纹扩展与缺口根部半径、热处理和添加维生素E之间的关系。具体而言，使用考虑缺口几何形状的修正应力强度因子来模拟裂纹驱动力。使用有限元方法进一步评估了每种材料/缺口组合的缺口塑性程度。在循环拉伸载荷下，考虑裂纹长度和缺口塑性，对裂纹速度与应力强度的函数关系进行了实验评估。结果表明，从缺口中产生的UHMWPE裂纹扩展主要受微观结构影响（交联），而非缺口几何形状差异的影响。
