The photographs of the sweep electron microscope show that fatigue damage are caused mainly by microcracks and impurities of metal.

通过疲劳断口的电镜扫描试验，证明防爆膜的疲劳破坏是由存在于金属内部的微裂纹和杂质所引起。

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The fatigue invalidation made by the kind of microcosmic and macroscopical mechanical stress concentrate 80% resulted in equipment part and metal components damage.

设备的零部件和金属构件发生的损坏，80%是由于各种微观和宏观机械应力集中所导致的疲劳失效。

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The fatigue damage of metal materials has been recognized in engineering field for a long time. And the fatigue damage problem of metal structures has become more and more serious.

金属材料的疲劳损伤是工程界早已发现的问题，金属结构的疲劳破损问题正日益突出。

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