Scheiner A, Mortimer J T, Kicher T P
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106.
J Biomed Mater Res. 1991 May;25(5):589-608. doi: 10.1002/jbm.820250504.
Single and multi-strand stainless steel and cobalt-nickel alloy wires, with strand diameters from 26 to 46 microns, were fatigue tested using a modified rotating bending test to determine what factors are most important in controlling fatigue life. The relation between cyclic strain and cyclic life was determined for each material by cyclically straining test specimens at various strain ranges and recording the number of cycles to failure. The results show that (a) the fatigue curves of the 316LVM, MP35N, DBS, and Syntacoben wires are very similar and have many of the same fatigue characteristics of specimens of large cross section. (b) Multi-stranded wires have the same average fatigue life as their individual constituent strands, but the variance of that life is smaller. (c) Deformities in the wire, which are created during the manufacturing, appear to have the effect of shortening the fatigue life of these small section wires. (d) Observation of wire fracture surfaces show a relatively small crack propagation zone and a large fast fracture zone suggesting that most of the fatigue life of these small wires is in the original crack formation, which creates a large stress concentration and quickly leads to wire failure. (e) The size of the wire cross sectional area is of secondary importance compared to the amplitude of the maximum cyclic strain of the individual strands in determining fatigue life of the cable. To maximize the fatigue life of electrodes in vivo, the highest fatigue life for a given bending radius of curvature is desired. This suggests wire strands should be manufactured at the smallest diameter possible (without introducing structural flaws) to maximize service life.
单股和多股不锈钢及钴镍合金丝，股线直径为26至46微米，采用改进的旋转弯曲试验进行疲劳测试，以确定控制疲劳寿命的最重要因素。通过在不同应变范围内对测试样本进行循环应变，并记录失效循环次数，确定了每种材料的循环应变与循环寿命之间的关系。结果表明：(a) 316LVM、MP35N、DBS和Syntacoben丝的疲劳曲线非常相似，并且具有许多与大横截面样本相同的疲劳特性。(b) 多股丝的平均疲劳寿命与其单个组成股线相同，但其寿命的方差较小。(c) 在制造过程中产生的丝材变形似乎会缩短这些小截面丝材的疲劳寿命。(d) 对丝材断口表面的观察显示，裂纹扩展区相对较小，快速断裂区较大，这表明这些细丝材的大部分疲劳寿命在于原始裂纹的形成，这会产生较大的应力集中并迅速导致丝材失效。(e) 与单个股线的最大循环应变幅度相比，丝材横截面面积的大小在确定缆线疲劳寿命时是次要的。为了使体内电极的疲劳寿命最大化，对于给定的弯曲曲率半径，需要最高的疲劳寿命。这表明股线应尽可能以最小直径制造（不引入结构缺陷）以最大化使用寿命。
