The fatigue failure process of steel can be divided into three stages: crack initiation, slow crack expansion, and final rapid fracture. In actual steel structures, due to the presence of tiny intrinsic defects, these defects act as cracks, so that fatigue failure usually only goes through two stages: slow crack expansion and final rapid fracture. Stress concentration accelerates the plastic deformation and hardening of grains, thereby reducing the fatigue strength of steel.

   It is worth noting that not all steel structures will suffer from fatigue failure. For steel structures with small load changes or infrequent cyclic loads, the risk of fatigue failure is low, and the influence of fatigue factors can be ignored during design calculations. However, for structures that are subjected to continuous cyclic loads for a long time, such as bridges and cranes, designers must fully consider the fatigue characteristics of steel.

  During the design process, the preventive measures for fatigue failure mainly include: optimizing structural design to reduce stress concentration; improving steel quality to reduce inherent defects; rationally selecting materials to improve the fatigue strength of steel; and regular inspection and maintenance to ensure structural safety.