Failure mode: according to the macro fracture surface and external economic observation results, the fracture characteristics of colorful bolts are basically the same, the total area of fatigue area is large, the total area of instantaneous fracture area is small, and there is fracture surface after the colorful bolt is cut off by external force of mechanical equipment. The failure mode of invalid bolt is fatigue fracture.

The fracture surface of the colorful bolt includes two fatigue fracture zones, one large and one small. The custom-made lantern rivet under all normal conditions, colorful bolts are generally subject to shear stress effect, and fatigue fracture is not allowed. From the fracture occurred in the cold heading head, and there are axial friction marks. There are also damage marks at the broken part of the bolt rod. It seems that the falling of the bolt head should be the fatigue fracture caused by the damage of the shaft body.

Invalid reason: according to the inspection of fracture surface of invalid bolt, there are no metallurgical industry defects such as miscellaneous in the fracture origin area, no abnormality in the alloy composition of automobile rivets, and the compressive strength of raw materials of hot heading head of colorful bolts is weaker than that of cold heading head, but the invalid fracture occurs at the cold pier end. Therefore, the fracture failure of colorful bolt riveting has nothing to do with the material.