PSI - Issue 23

M.A. Artamonov et al. / Procedia Structural Integrity 23 (2019) 257–262 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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For the specimens, tested with the asymmetry ratio of R=0.5, the difference in m factor as compared with the CT specimens is essential. Perhaps, the higher maximum levels of strain, demonstrated during the tests of specimens with the asymmetry ratio of R = 0.5, do not make it possible to calculate the values of C and m factors for certain by this method.

Conclusions

For a reliable description of the process of fracture in the materials, it is necessary to consider separately the process of crack initiation and the period of its propagation. This can be done with the use of fractographic analysis. The period of crack initiation and the duration of FCG in the cylindrical specimens made of nickel-based superalloy EP741NP depend on the temperature and cycle asymmetry. The crack initiation linearly depends on the level of maximum strain and temperature. It must be noticed that this dependence refers only to the case of crack initiation from the surface of specimen. The high lifetime of specimens during the tests at low temperatures is ensured by the duration of the fatigue crack initiation. The temperature exerts influence on the dynamics of FCG. For the cycle asymmetry of R=0 in the range of temperatures from 20 o C to 550 o C the durability does not decrease. The sharp decrease of durability takes place just at high temperatures. For the cycle asymmetry ratio of R = 0.5 the durability decreases in the whole range of temperatures. At that, beginning from the temperature of 550 o C the durability of specimens, tested at the cycle asymmetries of R = 0 and R = 0.5, coincides. The obtained results demonstrate the linear dependence of m factor of the Paris equation on temperature. The comparison of the obtained values of m coefficient for the cylindrical specimens with the CT specimens demonstrates their divergence at high temperatures. The other factor that exerts influence on the resultant durability is the duration of the fatigue crack propagation (the number of cycles when the transition from stable to unstable crack growth takes place), which may depend on the temperature and cycle asymmetry ratio. At a higher temperature and asymmetry the transition to the accelerated growth takes place at greater distances from the origin. 1. Chester T. Sims (Editor), Norman S. Stoloff (Editor), William C. Hagel (Editor), 1987. Superalloys II: High-Temperature Materials for Aerospace and Industrial Power, pp.640. 3. R. L. Saha, K. Gopinath, K. K. Sharma and M. Srinivas, 2001. Low cycle fatigue behaviour of alloy 718 disc forging at elevated temperatures, Superalloys 718, 625, 706 and derivatives, ed. by E.E.Loria, TMS. 4. W. L. Mills and C. M. Brown, 2001. Fatigue fracture surface morphology for alloy 718, Superalloys 718, 625, 706 and derivatives, ed. by E. E. Loria, TMS. 5. J. Warren, D.Y. Wei, 2006. The cyclic fatigue behaviour of direct aged 718 at 149, 315, 454 and 538°C, Materials Science and Engineering A 428, 106-115. 6. S. Deyber, F. Alexandre, J. Vaissaud and A. Pineau, 2005. Probabilistic life of DA718 for aircraft engine disks, Superalloys 718, 625, 706 and derivatives, ed. by E. E. Loria, TMS. 7. P.J.E. Forsyth and D. A. Ryder, 1961. ACTA Metallurgica 63:117. 8. 4. J. J. Au and J. S. Ke, 1980. Correlation between fatigue crack growth rate and fatigue striation spacing in AISI 9310 (AMS6265) steel, in ASTM STP733, pp. 202. 9. I. Nedbal, J. Siegl, J. Kunz, 1989. Relation between Striation Spacing and Fatigue Crack Growth Rate in Al-Alloy Sheets. In: Advances in Fracture Research (Proc. ICF 7). Eds. K.Salama et al. Vol.5. Oxford, Pergamon Press, pp. 3483 – 3491. 10. Shanyavskiy A.A., 2003. Bezopasnoye ustalostnoye razrusheniye elementov aviakonstruktsiy. Sinergetika v inzhenernykh prilozheniyakh [Tolerance fatigue failures of aircraft components]. – Ufa, Monografiya, pp. 803. 11. Ganeev A., Valitov V., Utyashev F., Imayev V., 2018. The influence of temperature-strain rate conditions on hot workability and microstructure of powder metallurgy nickel-based superalloy EP741NP. IOP Conf. Series: Materials Science and Engineering 447. 12. Landes J. D., Begley J. A., 1972. The J-integral as a fracture criterion. — Fracture Toughness ASTM STP 514, Phil, pp. 1 — 23. 13. ASTM international, 2000. ASTM Standard E1820-13: standard test method for measurement of fatigue crack growth rates. West Conshohocken, PA, ASTM International. 14. Potapov S.D., Perepelitsa D.D., 2014. Issledovanie vliyaniya geometricheskikh osobennostey treshchiny na kharakteristiki tsiklicheskoy treshchinostoykosti [Investigation of the effect of geometrical features of cracks on cyclic crack resistance characteristics]. Tekhnologiya legkikh splavov, № 1, pp. 66-71. References