ESTIMATION OF CRITICAL TEMPERATURES OF BRITTLE-DUCTILE TRANSITION AND BRITTLE FRACTURE ARREST CORRELATION BASED ON FINITE ELEMENT MODELLING

Abstract

In justifying the applicability of the steels for the manufacture of structures operating at low temperatures various methods of temperature control of viscous-brittle transition are widely used. The most physically reasonable, but also the most time consuming is the method of determining the temperature brittle fracture arrest ( T a ), when testing large-scale specimens-plates. In this connection there is a problem to justify the prediction temperature T a on the results of the more simple tests used in certification testing of sheets of low alloy steel. These include widely used test to determine the NDT — «temperature of zero plasticity», and testing to determine the temperature dependency of the fracture type ( T kb temperature — the static bending temperature, DWTT temperature — in impact bending). By numerical FEM simulation of the process of crack propagation in the specimen NDT received that determined in these tests the temperature of NDT corresponds to the critical stress intensity factor K 1 a during the crack arrest under plane strain conditions. This value is proportional to the material yield strength σ Y at given temperature. Based on the results of previous work of the authors linking temperature T a to the values of K 1 a , σ Y at given temperature and thickness of sheet metal t , correlation the ratio of the temperatures NDT and T a , taking into account the material thickness and its yield stress is proposed. To link the fracture of full thickness specimen with the crack arrest conditions, the numerical simulation of crack propagation in the specimen with a blunt notch T kb specimens was performed. It is shown fracture of specimens, loaded in full-scale yield, interpreted as the ratio of the quantities of the elements that «destroyed» by brittle mechanism, to the total number of elements in the plane of the fracture is in correlation with the condition of the crack arrest in a wide plate, loaded by the tension in the nominally elastic region. It is projected that in the determination of T kb as the temperature corresponding to 70% of the viscous component in the fracture, it lies significantly below the temperature T a .