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Fracture splitting notches from C70S6 steel used in a connecting rod and from gray cast iron used in an engine crankcase main bearing bracket were processed by a YAG pulse laser,and the fracture splitting experiment was conducted in the fracture splitting device.The geometry appearances,microstructures,micro-hardness change as well as the fracture surface of fracture splitting notches were studied by a tool microscope,a scanning electronic microscope and a micro-hardness tester.Characteristics of fracture splitting notches processed by the pulse laser were discussed,and the influence of pulse laser processing fracture splitting notches from ductile/brittle materials on the expansion and breaking performance of the notchs was revealed.The results indicate that the geometry appearances and notch effects of the fracture splitting notches from ductile/brittle materials processed by the pulse laser are obviously superior to those of the broaching and linear cutting processing,and the gap sensitivity of gray cast iron has been strengthened greatly.The brittle martensite has been produced nearby the fracture splitting notches from ductile/brittle materials,and micro crack appears in the root of notch.The organization is obviously refined.The micro-hardnesses of melting zone and the solid phase transition zone of ductile/brittle materials approximately are 820/850 HV and 860/550 HV,respectively,which are higher than that of the substrate,and show a remarkable hardening effect.The ductile tearing phenomenon can not be seen in the C70S6 steel notch root zone.The ductile/brittle material fracture shows the brittle fracture characteristic,which satisfies the fracture splitting technological requirement.