Eberhardt A W, Kim B S
Department of Materials and Mechanical Engineering, University of Alabama at Birmingham 35294-4461, USA.
J Biomech Eng. 1998 Dec;120(6):778-83. doi: 10.1115/1.2834893.
Pitting wear is a dominant form of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In the present study, stress intensity factors, KI and KII, were calculated for a surface crack in a polyethylene-CoCr-bone system in the presence of rolling or sliding contact pressures. Variations in crack length and load location were studied to determine probable crack propagation mechanisms and modes. The crack tip experienced a wide range of mixed-mode conditions that varied as a function of crack length, load location, and sliding friction. Positive KI values were observed for shorter cracks in rolling contact and for all crack lengths when the sliding load moved away from the crack. KII was greatest when the load was directly adjacent to the crack (g/a = +/- 1), where coincidental Mode I stresses were predominantly compressive. Sliding friction substantially increased both KImax and KIImax. The effective Mode I stress intensity factors, Keff, were greatest at g/a = +/- 1, illustrating the significance of high shear stresses generated by loads adjacent to surface cracks. Keff trends suggest mechanisms for surface pitting by which surface cracks propagate along their original plane under repeated reciprocating rolling or sliding, and turn in the direction of sliding under unidirectional sliding contact.
点蚀磨损是全膝关节置换中聚乙烯表面损伤的主要形式，可能源于在反复摩擦接触下扩展的表面裂纹。在本研究中，计算了在存在滚动或滑动接触压力的情况下，聚乙烯-钴铬合金-骨系统中表面裂纹的应力强度因子KI和KII。研究了裂纹长度和载荷位置的变化，以确定可能的裂纹扩展机制和模式。裂纹尖端经历了一系列随裂纹长度、载荷位置和滑动摩擦而变化的混合模式条件。在滚动接触中较短的裂纹以及当滑动载荷远离裂纹时所有裂纹长度下，均观察到正的KI值。当载荷直接邻近裂纹（g/a = +/- 1）时，KII最大，此时巧合的I型应力主要为压缩应力。滑动摩擦显著增加了KImax和KIImax。有效I型应力强度因子Keff在g/a = +/- 1时最大，说明了邻近表面裂纹的载荷产生的高剪切应力的重要性。Keff趋势表明了表面点蚀的机制，即表面裂纹在反复的往复滚动或滑动下沿其原始平面扩展，并在单向滑动接触下转向滑动方向。
