INDEX fracture toughness

The incorporation of a ceramic dispersion phase in a glass matrix leads to an increase in the effective hardness in comparison with that of the unreinforced matrix. On the other hand, metallic inclusions will usually have the opposite effect. The simultaneous modification of hardness (H) and fracture toughness (K c) in composite materials results in variations in the brittleness of the material, which can be quantified by the brittleness index (B), with B = HIKic [138],... 

Furthermore, validation work of different fracture toughness indexes was performed within the FP-4 project REFEREE. In this project the influence of dynamic loading (used for the surveillance specimens) on the shift of fracture toughness was studied with respect to the shift obtained under quasi-static loading (as is the case under real conditions in the RPV). 

Fig. 5.17 In-plane tear and fracture toughness index against PCC content for the new composite and reference paper. Commercial copy is a geometric mean value. Abbreviations C new composite handsheets. Fibre components reg.cellulose regenerated cellulose, euca eucalyptus unrefined, sw fractionated refined softwood...

With the reference toughness curve approach, the RT m index first came into use as the reference nil-ductility temperature which is determined in accordance with the ASME Code, Section III, Subsection NB-2331. The reference toughness Km curve and the Ki curve for static crack initiation later came into use as part of Section XI where the Km curve was called the crack arrest Xia curve. Thus, the RTndt reference temperature index has become the key material parameter in determining the allowable (P-T) limits for plant operation and for evaluating RPV integrity as the result of extreme transients such as PTS. Note that several years ago, the concept of a different, directly measured fracture toughness Master Curve approach was accepted in the ASME Code based on the index parameter RTjq. This development is covered in detail in Chapter 10. 

ASME Code Section III at first used the fracture analysis diagram (FAD) for the prevention of brittle fracture. Linear elastic fracture mechanics was introduced in 1972 Summer Addenda, Appendix G. ASME Code Section XI Appendix A and NRC Federal Register lOCFR Part 50 were issued in 1973. In these codes and regulations, RTndt was introduced as an important index temperature to characterize the transition curve of fracture toughness. 

Table 6.2 Fracture toughness curves and indexing to account for irradiation... 

However, more recently a new brittleness rationalized index, denoted and expressed in Jim , has been introduced by Quinn and Quinn from the National Institute of Standards and Technology (NIST) as the ratio of the deformation energy per unit volume to the fracture energy per unit surface area. This brittleness index is more accurate than the previous one because it includes three intrinsic properties of the material rather than only two. Therefore, brittleness can be described in terms of the micro Vickers hardness (HV), Young s modulus (E), and the fracture toughness of the ceramic materials (X, ), as described in the following rationalized Quinn s equation ... 

---