Gray iron castings material can easily form a kind stress, which exceeds its own breaking strength, under external force. Therefore, rupture defect is a key factor in failures of mechanical components.

According to analyses from related professionals, the rupture process of gray iron castings material is very complicated. In general, these 3 processes, including internal ruptures formation, extension and final rupture, are what experienced at necessary. The kind of rupture defects, where their rupture lines not causing obvious plastic deformations, belong to brittle rupture defects. Under normal force, brittle rupture results from separations of those reasonable and weakest crystallographic planes between these atoms and formation of ruptures, which is also called as cleavage fracture. When it comes to the fracture nucleation mechanism among gray iron castings, Dislocation Pile-up Theory thinks related dislocation motions resulting from some materials being stressed are blocked from grain boundaries and impurity phases so as to form dislocation pile-up among gray iron castings. Once the collection of stresses from pile-up groups exceed strength of materials, the front end places, where pile-up groups locate, will form breaks so that the front breaks of brittle rupture defects will extend rapidly.

Per analyses from stress relations, if the yield stress of gray iron castings material is more than either its own fracture nucleation stress or rupture stress, it’ll be fractured under non-plastic deformation state once forming some breaks.