CONSTRAINT EFFECTS ON REFERENCE TEMPERATURE, T-0, FOR FERRITIC STEELSIN THE TRANSITION REGION

This study presents the methodology and key results derived from stoch astic simulations to examine the effect of constraint loss on the refe rence temperature, T-0, at which the median fracture toughness of 1 T size specimens equals 100 MPa root m for ferritic steels in the transi tion region. Using the Weibull stress as a local fracture parameter fo r transgranular cleavage, nonlinear three dimensional finite element a nalyses provide a quantitative description of constraint loss along cr ack fronts in deeply-notched SE(B) specimens in terms of a toughness s caling model. The simulations employ a Monte Carlo procedure to genera te trial sets of small-scale yielding fracture toughness data which fo llow the three parameter Weibull distribution prescribed in the ASTM d raft standard to determine T-0. Reverse corrections of the SSY values using the toughness scaling model predict large-scale yielding Values (that would be measured in a fracture test). The differences in refere nce temperatures for the SSY and LSY toughness Values represent the sh ift due to constraint loss. Results of extensive experimental testing programs, complemented by these simulations, provide key information n eeded by testing standard committees to specify appropriate censoring (deformation) limits on measured fracture toughness data relative to s pecimen size and material flow properties. (C) 1998 Elsevier Science L td. All rights reserved.