Abstract: The stress of the hole of frogs on the railway have been estimated by means of mechanics of elasticity and finite element computation. The main reasons of the cracks induced from the hole have been found out by the analyses of metallurgie quality, machining process and SEM on the fracture. The critical size of the cracks ac and N-a curve have determined in the method of fracture mechanics.

Key words: 断裂, 高锰钢