A study of fatigue wear of the ultra-high molecular weight polythylene in terms of frictional heat

人工关节的润滑温度提高了10^。C由于摩擦产生的热量根据润滑剂的体积和接触压力而定。润滑油的温升受运动部件热性能的影响较大。约90%的摩擦热传递到超高分子量聚乙烯的配合部分。随着温度的升高，超高分子量聚乙烯的软化得到了证实。在简单倒向滑动条件下，摩擦系数随时间或滑动距离的增加而逐渐减小，约为初始值的一半。它对载荷条件比温度变化更敏感。利用红外辐射显微镜测量了超高分子量聚乙烯圆盘与蓝宝石玻璃板的接触温度。同时测量润滑油温度，并与接触温度进行比较。温升可达12^。在平均接触压力P__-=12.7 MPa，滑动速度50nm/s的条件下，观察30min后C的变化。在接触带附近，接触温度与润滑剂温度呈线性关系。实验研究表明，接触温度随时间的增量约为接触带附近润滑剂温度增量的2倍。该实验条件下的接触温升行为可以用均匀带热源模型的数学模型来解释。通过实测接触面积，利用赫兹接触理论估计超高分子量聚乙烯的杨氏模量为0.4 GPa。摩擦系数受接触压力分布的强烈影响。这一发现可用于通过改变股骨头的轮廓来改善髋关节的润滑状况，以达到最佳的接触压力分布。

Lubricant temperature of artificial joint increased up to 10^。C due to frictional heat according to the lubricant volume and contact pressure. Temperature increment of lubricant is strongly affected by the thermal properties of the moving part. About 90% of the frictional heat is transferred to the mating part of UHMWPE. The softening of UHMWPE was confirmed with an increment of temperature. The coefficient of friction decreased gradually with an increment of time or sliding distance to about a half of an initial value in a simple reciprocal sliding condition. It is sensitive to the loading conditions rather than temperature changes. The contact temperature between UHMWPE disk and the sapphire glass plate was measured by the infrared radiometric microscope. Lubricant temperature was measured simultaneously and compared with the contact temperature. Temperature rise up to 12^。C was observed in 30 minutes under a condition of the mean contact pressure P__-=12.7 MPa and sliding speed 50nm/s. There was a linear relation between contact temperature and lubricant temperature in the vicinity of the contact band. From this experimental study, it was clarified that an increment of contact temperature with time was about two times higher than that of lubricant temperature near the contact band. The behavior of contact temperature increment in this experimental condition could be explained by a mathematical model of a uniform band heat source model. The Young's modulus of UHMWPE was estimated as 0.4 GPa by using Hertzian contact theory through the measurement of real contact area. The coefficient of friction is strongly influenced by the contact pressure distribution. This finding could be used to improve the lubricating condition of the hip joints by changing the profile of the femoral head to make an optimum contact pressure distribution.