Research Of Microsopic Failure Mechanism Of Ferritic Ductile Iron Based On Finite Element Simulation

Because of excellent toughness, damping properties, wear resistance, casting performance and lower production costs, ferritic ductile cast iron has emerged as an important structure and transmission materials and has been widely used in industrial production. Deep understanding of ferritic ductile cast iron micro-failure mechanism helps to analyze its service performance and toughening alloy. With the help of in-situ mechanical observation methods and finite element simulation software for ferritic ductile, it’s the microscopic deformation and crack initiation/propagation under different loads were analyzed, the microscopic failure mechanism and influences factors were proposed. The paper get the following conclusions:(1) Under uniaxial tensile tests, cracks near the deformed graphite nodular carried into hollows. At the same time, cavities generated around the grain boundaries and the inclusions. Connected and polymerization of the hollows and the cavities lead to final fracture.(2) Finite element simulation results shows that the matrix near the interface graphite/ferrite is stress concentration area and easy to initiate cracks. Stress concentration in graphite reunion area is more obvious, graphite dispersion maximum principal stress is 267.87MPa and the reunion is 353.21MPa. The better roundness and compactness of the graphite nodular and very small amount of pearlite has a small effect on initiate cracks. The graphite with poor roundness and compactness split the matrix and leads to severe stress concentration, in ferrite ductile cast iron tensile test is not destructive.(3) Two-dimensional extended finite element results show that, cracks initiate in the interface of graphite/ferrite matrix under the static tensile loads, and propagate more likely into the matrix. The simulation results greatly agree with the experimental results.(4) Under instantaneous impact load, the changing pathway of the crack propagation because of the graphite improves the new interface energy and results in an increase in fracture stress, no graphite model is 563N, fracture energy is 5343.71mJ, while one/ four graphite model respectively increase to 932.81N and 1406.36N, fracture energy increase to 8626.95mJ and 9568.19mJ. Under the axial alternate load graphite reduced the crack growth rate greatly and improved fatigue life of the ferritic ductile dust iron.