fatigue crack propagation

例句：

1. 1. The fatigue crack propagation in the welded joint was monitored using ultrasonic testing.
   使用超声波测试监测焊缝中的疲劳裂纹扩展。
2. 2. Fatigue crack propagation is a significant concern in the design of structures.
   疲劳裂纹扩展是结构设计中的一个重要问题。
3. 3. The research on fatigue crack propagation has greatly improved the durability of materials.
   关于疲劳裂纹扩展的研究极大地提高了材料的使用寿命。