Elbert K E, Wright T M, Rimnac C M, Klein R W, Ingraffea A R, Gunsallus K, Bartel D L
Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York 14853.
J Biomed Mater Res. 1994 Feb;28(2):181-7. doi: 10.1002/jbm.820280207.
Analytical studies of the stresses on and within ultra high molecular weight polyethylene joint components suggest that damage modes associated with polyethylene fatigue failure are caused by a combination of surface and subsurface crack propagation. Fatigue crack propagation tests under mixed mode loading conditions were conducted on center-cracked tension specimens machined from extruded blocks of sterilized polyethylene in an attempt to determine how fatigue cracks change direction in this material. Cyclic testing was performed using a sinusoidal wave form at a frequency of 5 Hz and an R-ratio (minimum load/maximum load) of 0.15. Specimens had the notch oriented perpendicular to the direction of applied load and at angles of 60 degrees and 45 degrees to the loading direction. Numerical analyses were used to interpret the experimental test and to predict the fatigue behavior of polyethylene under mixed mode conditions. It was found that all cracks eventually propagated horizontally, regardless of the initial angle of inclination of the notch to the direction of applied cyclic load. In fact, the extent of the curvilinear crack growth was quite limited. An effective range of cyclic stress intensity factor was calculated for correlation with the rate of crack growth. The results followed a Paris relation, with crack growth rate linearly related to a power of the range of stress intensity, for all three crack orientations. The numerical analyses adequately modeled the experimental fatigue crack growth results.
对超高分子量聚乙烯关节部件上及其内部应力的分析研究表明，与聚乙烯疲劳失效相关的损伤模式是由表面和亚表面裂纹扩展共同造成的。对从经过灭菌处理的聚乙烯挤压块加工而成的中心裂纹拉伸试样进行了混合模式加载条件下的疲劳裂纹扩展试验，以试图确定疲劳裂纹在这种材料中如何改变方向。使用正弦波形在5Hz频率和0.15的R比率（最小载荷/最大载荷）下进行循环测试。试样的切口方向垂直于施加载荷的方向，并与加载方向成60度和45度角。采用数值分析来解释试验结果，并预测混合模式条件下聚乙烯的疲劳行为。结果发现，所有裂纹最终都水平扩展，无论切口相对于施加的循环载荷方向的初始倾斜角度如何。实际上，曲线裂纹扩展的程度相当有限。计算了循环应力强度因子的有效范围，以与裂纹扩展速率相关联。对于所有三种裂纹取向，结果均符合巴黎关系，即裂纹扩展速率与应力强度范围的幂次呈线性关系。数值分析对实验疲劳裂纹扩展结果进行了充分的模拟。
