Development of Mechanical and Fatigue Testing System for Micro Elements

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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.