Fracture Analysis on Outer Chain Plate of an Escalator Main Drive Chain

The outer chain plate of an escalator main drive chain fractured during operation. The fracture causes of the outer chain plate were analyzed by macroscopic inspection, chemical composition analysis, hardness test, non-metallic inclusion inspection and metallographic examination. The results show that the surface printed word bottom of the outer chain plate had a sharp corner and folding defect, and there was surface decarburization on some raw material surface of the outer chain plate, which resulted in stress concentration at word bottom of the outer chain plate and decrease of the fatigue resistance of the material surface. Under the action of multiple stresses, the fatigue crack source originated from the bottom defect of the outer chain plate, and the cracks continuously expanded, which eventually led to fatigue fracture failure of the outer chain plate.