PSI - Issue 13

Hans-Jakob Schindler / Procedia Structural Integrity 13 (2018) 398–403 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

403

6

becomes minimum. Therefore, it is beneficial to define a reference temperature T x as close to upper shelf as possible. If a standardized specimen like the one suggested in Sec. 3.1 is used, validity in the sense of J-controlled initiation of cleavage is no longer relevant, as long as cleavage is initiated without a significant amount of prior ductile tearing. For example, T x could be defined as the temperature where J reaches 90% of J at 0.2 mm ductile tearing. From the data shown by Schindler (2014) it is expected that at this level of J two or three tests are sufficient to obtain a reasonably accurate T x , from which T 0 can be calculated by (5). As a matter of fact, the existing standards for fracture toughness testing are seldom used in practice, which is likely to be due to their complexity. They obviously do not meet the needs of practitioners. Estimates of K Ic or J Ic from correlations with CV-data are usually sufficient and preferred. However, these correlations could be improved considerably by tests that are comparably simple as CV-tests but closer to fracture toughness tests in terms of constraints and notch sharpness. A key issue is the specification of a suitable standard specimen. The main benefit of a suitable standardized specimen is that no validity criteria are required anymore. In the present paper, a Charpy-type specimen with a deep EDM-cut as a notch is suggested. This or a similar specimen should be standardized, as well as the definition of a suitable reference temperature T x and the corresponding  T 0//x for the use in (5) and a simple evaluation in case of upper-shelf behavior as suggested by eq. (4). The corresponding experimental work is not done yet. However, there is no doubt that such a standard would simplify fracture toughness measurement dramatically, and that the results would be more reliable than estimates from CV-data. The resulting characteristic J or T x - values would be as useful for practical use as the current standard fracture toughness or T 0 values, respectively. Nanstadt, R., et al., 2009, IAEA coordinated research project on MC approach …, Proc. ASME PVP Devision conference, PVP2009, Prague. Schindler, H.J., 2000, Realtion between fracture toughness and Charpy fracture energy: An analytical approach., ASTM STP 1380, T.A. Sieverts and M.P. Manahan, Eds., American. Soc. Testing and Materials, West Conshohocken. Schindler, H.J., Kalkhof, D., 2013, Lower bounds and saturation effects of dynamic fracture toughness in the brittle to ductile transition regime, Transactions, SMiRT-22, San Francisco, Ca. Schindler H.J., Kalkhof D., Viehrig, H.W., 2014, Effect of notch acuity on the apparent fracture toughness, Engineering Fracture Mechanics, 129, 26 – 37 Schindler, H.J., 2014, Fracture Toughness of Ferritic Steels: Lower Bounds and their Implications on Testing and Application, Procedia Engineering 86, 247 – 257. Sokolov, M.A., Nanstadt, R.K., 1999, Comparison of irradiation induced shift of K Jc and Charpy impact toughness, ASTM STP 1225, American. Soc. Testing and Materials, West Conshohocken. 5. Summary and Outlook References