Development of Mechanical and Fatigue Testing System for Micro Elements

为了在服役中开发可靠的微系统，必须对μm尺寸微元件的力学性能(包括疲劳行为)进行细观力学评估。然而，评价方法还没有建立起来。在这项研究中，已经开发了微元素在拉伸和弯曲载荷下的力学测试系统，从而可以在1-200赫兹进行疲劳试验。此外，对厚度为1μm和3μm的SiN薄膜进行了力学测试，考察了样品尺寸和加载方式的影响：拉伸强度随样品尺寸的减小而增大。然而，弹性模数与样品大小无关，尽管它取决于沉积方法。与拉伸载荷下的弯曲强度相比，弯曲强度对样品大小的依赖性较小。然而，抗弯强度高于抗拉强度，这表明微元件的强度高度依赖于加载方式。此外，还研究了微小人工缺陷和疲劳载荷对光纤性能的影响。材料的抗拉强度对环境极为敏感，即使在真空度为10℃~(-5)~(-5)Pa时，材料的抗拉强度也随水分含量的增加而降低：在单调和循环疲劳载荷作用下，强度均随水分子分压的增大和加载速率的降低而降低。提出了在恒定和循环疲劳载荷作用下的寿命估算方法。该方法基于对由拉伸试验和慢应变速率拉伸试验得出的裂纹扩展规律的评估，用该方法估算的寿命与实验数据相吻合。

In order to develop a reliable micro system in a service operation, much care must be taken into micro mechanical evaluation, i.e., mechanical properties of μm-sized microelements including fatigue behavior. However, the evaluation method has not yet been established. In this investigation, mechanical testing systems for microelements under tensile and bending loads have been developed, and thereby fatigue testing at 1-200 Hz is possible. Moreover, mechanical tests were conducted for SiN thin films of 1 μm and 3 μm thick, and the effects of sample size and loading mode were investigated : the tensile strength increased with a decrease in sample size. However, the elastic modulus was independent of sample size, although it is dependent on a deposition method. Bending strength is less dependent on the sample size compared with those under tensile loading. However, the bending strength was higher than the tensile strength, indicating that the strength of a microelement is highly dependent on the loading mode. Moreover, the influence of micro artificial defect and fatigue loading on an optical fiber was investigated. The tensile strength was extremely sensitive to an environment, and the tensile strength decreased by moisture containing even in a vacuum at 10^<-5> Pa : the strength decreased with an increase in a partial pressure of water molecule and with a decrease in loading rate under both monotonic and cyclic fatigue loading. The estimation method for evaluating the life under constant and cyclic fatigue loading was proposed. The method was based upon evaluating a crack growth law, derived by tensile tests and slow strain rate tensile testing, and the life evaluated by using the proposed method agreed with experimental data.