18th International Conference on Structural Mechanics in Reactor Technology (SMiRT 18) Beijing, China, August 7-12, 2005 SMiRT18-G01-5 USE OF THE MASTER CURVE METHODOLOGY FOR REAL THREE DIMENSIONAL CRACKS Kim Wallin VTT Industrial Systems P.O. Box 1704, FIN-02044VTT Phone: +358 20 722 6870, Fax: +358 20 722 7002 E-mail: kim.wallin@vtt.fi Rauno Rintamaa VTT Industrial Systems P.O. Box 1704, FIN-02044VTT Phone: +358 20 722 6879, Fax: +358 20 722 7002 E-mail: rauno.rintamaa@vtt.fi ABSTRACT At VTT, development work has been in progress for 15 years to develop and validate testing and analysis methods applicable for fracture resistance determination from small material samples. The VTT approach is a holistic approach by which to determine static, dynamic and crack arrest fracture toughness properties either directly or by correlations from small material samples. The development work has evolved a testing standard for fracture toughness testing in the transition region. The standard, known as the Master Curve standard is in a way ”first of a kind”, since it includes guidelines on how to properly treat the test data for use in structural integrity assessment. No standard, so far, has done this. The standard is based on the VTT approach, but presently, the VTT approach goes beyond the standard. Key components in the standard are statistical expressions for describing the data scatter, and for predicting a specimen’s size (crack front length) effect and an expression (Master Curve) for the fracture toughness temperature dependence. The standard and the approach it is based upon can be considered to represent the state of the art of small specimen fracture toughness characterization. Normally, the Master Curve parameters are determined using test specimens with "straight" crack fronts and comparatively uniform stress state along the crack front. This enables the use of a single K I value and single constraint value to describe the whole specimen. For a real crack in a structure, this is usually not the case. Normally, both K I and constraint varies along the crack front and in the case of a thermal shock, even the temperature will vary along the crack front. A proper means of applying the Master Curve methodology for such cases is presented here. Keywords: Master Curve, 3D-cracks, brittle fracture, constraint. 1. INTRODUCTION The master curve method is a statistical, theoretical, micromechanism based, analysis method for fracture toughness in the ductile to brittle transition region. The method, originally developed at VTT Manufacturing Technology” simultaneously account for the scatter, size effects and temperature dependence of fracture toughness, as schematically presented in Fig. 1 (Wallin, 1999). The method has been successfully applied to a very large number of different ferritic steels and it forms the basis of the ASTM testing standard for fracture toughness testing in the transition region (ASTM E1921-02). Worldwide, there is ongoing comprehensive validation and development work to include the Master Curve method, as a new reference fracture toughness concept, into different structural integrity assessment codes, like ASME. Copyright © 2005 by SMiRT18 1423