Study On Ductile Fracture Of High Strength Steel Based On Guron Model

Research on the microcosmic structure view of the crack tip during the damage of material is the trend of the development of current fracture mechanics. The ductile materials are often carrying imperfection in form of inclusion, cavities and so on; they affect the behavior of materials during their active service. Therefore, it is a vital problem to describe these changes of micro-plastic damage during the ductile fracture process and this is necessary to evaluate the safety of the materials for and their reliability. But in the traditional fracture mechanics, the criterion with macroscopic fracture parameters often has limitations, especially in analyzing and revealing crack initiation and evolution. So, with the combinations of damage mechanics and fracture mechanics, research object damage phenomenon, to study the fracture of ductile materials is a pioneering field. From the last century, domestic and foreign scholars put forward a lot of mathematical model to describe the deeper mechanism of the plastic deformation, during which the most widely used is the Gurson-Tvergaard model, hereinafter referred to as the G-T model. In this model, the major difference with the traditional models is that it considers the effect of the hydrostatic stress and the void volume fraction. After that, in 1995, Xia and Shih proposed the―computational cell‖approach, providing an engineering means to predict the fracture resistance in structural geometries with crack-like defects; this makes realization for computer technology in numerical simulation of crack propagation.In this study, the Q420 steel is chosen as the test material. The uniaxial tension test and three test bending test are conducted. At the same time, with the consideration of the G-T model for plastic damage, adopting the computational cell approach, the parameters controlling ductile crack growth are calculated from the finite element numerical method. Moreover, damage distribution ahead of the crack-tip and the stress triaxiality is also analyzed. The study reveals that the computational cell approach can effectively describe the behavior of ductile crack growth and make different types of fracture of the same material predictable.