A THEORY OF CLEAVAGE CHARACTERISTIC STRESS ON LOW-TEMPERATURE CLEAVAGE FRACTURE IN MILD-STEEL - A REVIEW

A theory of cleavage characteristic stress on cleavage fracture in mild steel is briefly reviewed. The theory involves two important concepts. First, a cleavage fracture stress (termed a cleavage characteristic stress S(co)) corresponding to the brittle/ductile transition in plain tension tests is a characteristic parameter resistant to low-temperature cleavage fracture of mild steel. It is intrinsically a lower bound value required to propagate an initial cleavage crack, which has advantageous stress and location conditions and has not blunted across grain boundaries. It controls cleavage fracture and brittle/ductile conditions of not only plain-tension specimens but also notched or cracked specimens of mild steel. Initiation and propagation of a cleavage crack are stochastic processes. In order to meet the probabilistic conditions of initiation and propagation of a cleavage crack, an effective yield zone has to be formed in which the maximum principal stresses are all more than or equal to S(co).