Over time, microscopic flaws in the material can grow into cracks that open a small amount with each loading cycle, even if those loading cycles are well below the metal's yield strength.

随着时间的推移， 材料中的微观缺陷会发展成裂纹， 在每个加载周期中都会打开少量裂纹，即使这些加载周期远低于金属的屈服强度。