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Evaluation of Mechanical Properties of Microelements and Environmental Strength under Dynamic Loading

动态载荷下微元力学性能和环境强度评价

基本信息

批准号：
09450048
负责人：
KOMAI Kenjiro
金额：
$ 8.96万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09450048/
关键词：
Microelement Micromachine Environmental Strength under Dynamic Loading Small Notch Effects Fatigue Vacuum Effects Water Environment Atomic Force Microscopy 曲げ強度引張強度疲労強度高強度・高弾性繊維

项目摘要

The fracture and fatigue behavior of micromaterials including single-crystal Si microelements and an advanced fiber reinforcement of aramid fiber have been performed. The specially designed testing machines are developed, which are capable of performing quasi-static and fatigue tests in mum sized microelements. Single crystal Si microelements deform elastically until final failure, giving a brittle nature. The fracture strength increases with a decrease in specimen size, and the maximum fracture strength is about 7.7 GPa. However, Si microelements are sensitive to notch, and sub-mum deep notch introduced by focused ion beam decreases the fracture strength. As for fatigue loading, no fatigue damage is observed even though the surface is nanoscopically examined by an atomic force microscope. However, in water, the fatigue lives are decreased : crack formation is promoted by a synergistic effect of dynamic loading and water environment. Atomic force microscopy is capable of imaging a nanoscopic crack, which causes the failure in water. The fiber strength of aramid fiber, Kevlar 49, is strongly influenced by an environment : water absorption and vacuum conditioning decrease the fracture strength. As for fatigue, aramid fibers have excellent fatigue properties, compared with metallic materials, showing gentle slope in s-N curves, although they have large scatter band. As for vacuum effects, the fatigue strength in vacuum is higher than that conducted in air. The fiber breaks with fiber splitting, and the fiber surface damage induced by fatigue loading in air and in vacuum was examined by using an atomic force microscope, and the influence of environment on fatigue and damage mechanisms are discussed.

研究了单晶硅微元素和高级纤维增强材料芳纶纤维的断裂和疲劳行为。研制了专门设计的试验机，可对微量元素进行准静态和疲劳试验。单晶硅微元素具有弹性变形，直至最终失效，具有脆性。断裂强度随试样尺寸的减小而增大，最大断裂强度约为7.7 GPa。而Si元素对缺口敏感，聚焦离子束引入的亚mum深缺口降低了断裂强度。对于疲劳载荷，采用原子力显微镜对其表面进行纳米级观察，也未观察到疲劳损伤。然而，在水中，疲劳寿命降低，动载荷和水环境的协同作用促进了裂纹的形成。原子力显微镜能够成像纳米级的裂纹，这导致了在水中的破坏。芳纶纤维（Kevlar 49）的纤维强度受环境影响较大，吸水率和真空调理降低了其断裂强度。在疲劳方面，与金属材料相比，芳纶纤维具有优异的疲劳性能，s-N曲线斜率较缓，但散射带较大。对于真空效应，真空中的疲劳强度高于空气中的疲劳强度。利用原子力显微镜观察了空气和真空环境下纤维的断裂和疲劳载荷对纤维表面的损伤，并讨论了环境对疲劳损伤的影响及损伤机理。