Issue 2

E. Lucon, Frattura ed Integrità Strutturale, 2(2007) 2-9 9 I valori di tenacità dinamica (normalizzati allo spessore di riferimento – 1 pollice) sono rappresentati in funzione della differenza tra la temperatura di prova e la tempera- tura di riferimento T o calcolata per il relativo materiale; questo tipo di rappresentazione consente di riunire sullo stesso grafico materiali diversi tra loro. La Fig. 7 costitui- sce un'ulteriore dimostrazione che il metodo della Master Curve è perfettamente applicabile a misure di tenacità di- namica su provini PCVN. Esempi di misure dinamiche di resistenza alla frattura duttile, ottenute mediante la metodologia Low Blow Test precedentemente descritta, sono mostrati per due tipici acciai da vessel nella Fig. 8, dove le curve dinamiche (in rosso) sono confrontate alle curve J-R ottenute in condi- zioni quasi-statiche (in blu) alle stesse temperature di prova. La Fig. 8 consente di apprezzare chiaramente l'in- cremento della resistenza alla frattura duttile, conseguen- te ad un aumento della velocità di deformazione. 6 BIBLIOGRAFIA [1] ASTM E399-05, Standard Test Method for Linear- Elastic Plane-Strain Fracture Toughness K Ic of Metallic Materials, Annual Book of ASTM Standards 2006, Vol. 03.01. [2] ASTM E1820-05a, Standard Test Method for Meas- urement of Fracture Toughness, Annual Book of ASTM Standards 2006, Vol. 03.01. [3] ISO 12135:2002, Metallic materials -- Unified method of test for the determination of quasistatic frac- ture toughness. [4] BS 7448-3:2005, Method for determination of frac- ture toughness of metallic materials at rates of increase in stress intensity factor greater than 3.0 MPa √ m/s, British Standards Institution. [5] ASTM E1921-05, Standard Test Method for Deter- mination of Reference Temperature, T o , for Ferritic Steels in the Transition Range, Annual Book of ASTM Stan- dards 2006, Vol. 03.01. [6] J.B. Hall e K.K. Yoon, Quasi-Static Loading Rate Effect on the Master Curve Reference Temperature of Ferritic Steels and Implications, Proceedings of the 2003 ASME Pressure Vessels and Piping Conference (Cleve- land, OH, 28-31 luglio 2003). [7] T.J. Koppenaal, Dynamic Fracture Toughness Meas- urements of High-Strength Steels Using Precracked Charpy Specimens, ASTM STP 563, 1974, pp. 92-117. [8] K.R. Iyer and R.B. Miclot, Instrumented Charpy Testing for Determination of the J-Integral, ASTM STP 563, 1974, pp. 146-165. [9] HTGR Fracture Toughness Program, EPRI NP-120, Project 337-1, Final Report, aprile 1976. [10] Proceedings of C.S.N.I. Specialist Meeting on In- strumented Precracked Charpy Testing, EPRI NP-2102- LD, Palo Alto, California, 1-3 dicembre 1980. [11] H.-W. Viehrig e E. Lucon, IAEA Coordinated Re- search Project on Master Curve Approach to Monitor Fracture Toughness of RPV Steels: Effect of Loading Rate, Proceedings of PVP2007, ASME Pressure Vessels and Piping Division Conference, 22-26 luglio 2007, San Antonio, Texas. [12] E. Lucon e H.W. Viehrig, Round-Robin Exercise on Instrumented Impact Testing of Precracked Charpy Specimens (IAEA Coordinated Research Program Phase 8), Proceedings of PVP2007, ASME Pressure Vessels and Piping Division Conference, 22-26 luglio 2007, San Antonio, Texas. [13] K. Wallin, Effect of Strain Rate on the Fracture Toughness Reference Temperature T o for Ferritic Steels, in: Recent Advances in Fracture (ed. R.K. Mahidhara et al.; The Minerals, Metals & Materials Society, 1997). [14] ISO TC 164/SC4 N465.3, Steel - Measurement of fracture toughness at impact loading rates using pre- cracked Charpy V-notch test pieces, ultima revisione: 27 ottobre 2006. [15] ESIS TC5, Proposed standard methods for instru- mented pre-cracked Charpy impact testing of steels and other metallic materials, Draft 25.4: dicembre 2005. [16] J.F. Kalthoff, S. Winkler and W. Böhme, A Novel Provedure for Measuring the Impact Fracture Toughness K Id with Precracked Charpy Specimens, Journal de Phy- sique, Colloque C5, supplement au n°8, Tome 46, agosto 1985, pp 179-186. [17] H. J. MacGillivray e D. F. Cannon, The Develop- ment of Standard Methods for Determining the Dynamic Fracture Toughness of Metallic Materials, ASTM STP 1130, 1992, pp. 161-179. [18] W. Böhme, Experience with Instrumented Charpy Tests obtained by a DVM Round Robin and further De- velopments, ESIS 20, Ed. E. van Valle, MEP Publica- tions, London, 1996, pp. 1-23. [19] J.A. Joyce, Static and dynamic J-R curve testing of A533B steel using the Key-curve analysis technique, ASTM STP 791, 1983, pp. I-543-I560. [20] H.J. Schindler, Estimation of fracture toughness from Charpy tests – theoretical relations, ASTM STP 1380, 1999, 340ff. [21] E. Lucon, The Use of Single-Specimen Techniques for Measuring Upper Shelf Toughness Properties under Impact Loading Rates, rapporto BLG-1016, SCK•CEN, settembre 2005.