Calibration of Weibull stress parameters using fracture toughness data

• Published in: International journal of fracture 1998-01, Vol.92 (2), p.175-200
• Main Authors: GAO, X, RUGGIERI, C, DODDS, R. H
• Format: Article
• Language: English
• Subjects: Applied sciences; Bend ductility; Calibration; Compact tension; Ductile fracture; Ductile-brittle transition; Exact sciences and technology; Ferritic stainless steels; Fracture mechanics; Fracture mechanics (crack, fatigue, damage...); Fracture mechanics, fatigue and cracks; Fracture toughness; Fractures; Fundamental areas of phenomenology (including applications); Measurement and testing methods; Measurement methods and techniques in continuum mechanics of solids; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Micromechanics; Parameters; Physics; Solid mechanics; Stress concentration; Structural and continuum mechanics; Structural steels
• ISSN: 0376-9429; 1573-2673
• DOI: 10.1023/a:1007521530191

The Weibull stress model for cleavage fracture of ferritic steels requires calibration of two micromechanics parameters . Notched tensile bars, often used for such calibrations at lower-shelf temperatures, do not fracture in the transition region without extensive plasticity and prior ductile tearing. However, deep-notch bend and compact tension specimens tested in the transition region can provide toughness values under essentially small-scale yielding (SSY) conditions to support Weibull stress calibrations. We show analytically, and demonstrate numerically, that a nonuniqueness arises in the calibrated values, i.e., many pairs of provide equally good correlation of critical Weibull stress values with the distribution of measured (SSY) fracture toughness values. This work proposes a new calibration scheme to find which uses toughness values measured under both low and high constraint conditions at the crack front. The new procedure reveals a strong sensitivity to m and provides the necessary micromechanical values to conduct defect assessments of flawed structural components operating at or near the calibration temperature in the transition region. Results of a parameter study illustrate the expected values of m for a typical range of material flow properties and toughness levels. A specific calibration is carried out for a mild structural steel (ASTM A36).