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 mil d steel is briefly reviewed. The theory involves two important concept s. First, a cleavage fracture stress (termed a cleavage characteristic stress S(co)) corresponding to the brittle/ductile transition in plai n tension tests is a characteristic parameter resistant to low-tempera ture cleavage fracture of mild steel. It is intrinsically a lower boun d value required to propagate an initial cleavage crack, which has adv antageous stress and location conditions and has not blunted across gr ain boundaries. It controls cleavage fracture and brittle/ductile cond itions of not only plain-tension specimens but also notched or cracked specimens of mild steel. Initiation and propagation of a cleavage cra ck are stochastic processes. In order to meet the probabilistic condit ions of initiation and propagation of a cleavage crack, an effective y ield zone has to be formed in which the maximum principal stresses are all more than or equal to S(co).