Determination of decohesion stress in cast iron matrix basing on the brittle fracture criterion and yield condition

Problems discussed in this study are related with the determination of the critical value of stress which, when exceeded, will cause the decohesion of cast iron matrix in accordance with the Ludwik – Scheu criterion and yield condition. The values of the effective stress σef present in the matrix and examined in function of the nominal stress σnom present on a boundary of the examined area were determined by the finite element method (FEM) for selected graphite shapes. The study proves that from the run of function σef = f(σnom) and using one of the above mentioned criteria one can judge about the mode of fracture and about the value of the stress intensity factor KI of the matrix. The determination of function σef = f(σnom) for a given configuration of the matrix type and graphite precipitates shape and distribution effectively eliminates the computing problems resulting from the fundamental assumption adopted in the classical continual fracture mechanics that the examined material is a continuum.