PSI - Issue 5

M. Dabiri et al. / Procedia Structural Integrity 5 (2017) 385–392 M. Dabiri et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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 Modified versions of Neuber’s rule and SED significantly improve their estimations in plane strain conditions. The life predictions by the latter are fairly close to the results of the elastic-plastic finite element model.  The elastic-plastic finite element model can be considered an accurate method in notch analysis, provided that the stabilized cyclic stress-strain response is introduced precisely. Although the use of simple hardening rules, such as isotropic hardening, is justified for analysis of notched components, the model needs to be run for a few virtual cycles to achieve stabilization. More complex hardening rules are required to model cyclic hardening/softening and other cycle-dependent transient behaviours.  TCD is a promising approach that can be easily coupled with the same model used in elastic-plastic finite element analysis without any further modifications. In addition, this method minimizes the level of conservatism in life predictions, especially in components with sharp notches. This study has been performed as part of the Breakthrough Steels and Applications (BSA) program funded by the Finnish Funding Agency for Innovation (TEKES) and the Digital, Internet, Materials & Engineering Co-Creation (DIMECC). The authors thank Dr. Matti Isakov from Tampere University of Technology for his cooperation in performing the experiments. References Dabiri, M., Isakov, M., Skriko, T. & Björk, T., 2016. Experimental fatigue characterization and elasto-plastic finite element analysis of notched specimens made of direct-quenched ultra-high strength steel. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, in press. Dowling, N., Brose, W. & Wilson, W., 1979. Notched member fatigue life predictions by the local strain approach. In: Advances in Engineering. Warrendale: Society of Automotive Engineers, SAE, pp. 55-84. Fatemi, A., Zeng, Z. & Plaseied, A., 2004. Fatigue behavior and life predictions of notched specimens made of QT and forged microalloyed steels. International Journal of Fatigue, Volume 26, pp. 663-672. Fricke, W., 2012. IIW recommendations for the fatigue assessment of welded structures by notch stress analysis. s.l.:Woodhead Pub.. Gates, N. & Fatemi, A., 2016. Notch deformation and stress gradient effects in multiaxial fatigue. Theoretical and Applied Fracture Mechanics, Volume 84, pp. 3-25. Jones, R., Knopp, M., Price, J. & Molent, L., 1998. Stress and Strain Estimation at Notches in Aircraft Structures, Melbourne: DSTO Aeronautical and Maritime Research Laboratory. Molski, K. & Glinka, G., 1981. A method of elastic-plastic stress and strain calculation at a notch root. Materials Science and Engineering, Volume 50, pp. 93-100. Neuber, H., 1958. Kerbspannungslehre (in German). Berlin: Springer. Neuber, H., 1961. Theory of stress concentration for shear-strained prismatical bodies with arbitrary nonlinear stress strain laws. Journal of Applied Mechanics, Volume 28, pp. 544-550. Peterson, R., 1959. Notch Sensitivity. In: Metal Fatigue. New York: MacGraw Hill, pp. 293-306. Peterson, R. E., 1974. Stress concentration factors. s.l.:John Wiley & Sons. Siebel, E. & Stieler, M., 1955. Significance of dissimilar stress distributions for cyclic loading. Zeitschr. VDI, Volume 97, pp. 146-148. Susmel, L., 2008. The theory of critical distances: a review of its applications in fatigue. Engineering Fracture Mechanics, Volume 75, pp. 1706 1724. Susmel, L., Atzori, B., Meneghetti, G. & Taylor, D., 2011. Notch and mean stress effect in fatigue as phenomena of elasto-plastic inherent multiaxiality. Engineering Fracture Mechanics, Volume 78, pp. 1628-1643. Susmel, L. & Taylor, D., 2010. An elasto-plastic reformulation of the theory of critical distances to estimate lifetime of notched components failing in the low/medium-cycle fatigue regime. Journal of Engineering Materials and Technology, Volume 132, pp. 021002-1-8. Susmel, L. & Taylor, D., 2015. Estimating lifetime of notched components subjected to variable amplitude fatigue loading according to the elastoplastic theory of critical distances. Journal of Engineering Materials and Technology, Volume 137, pp. 011008-1-15. Tanaka, K., 1983. Engineering formulae for fatigue strength reduction due to crack-like notches. International Journal of Farcture, Volume 22, pp. 39-46. Taylor, D., 1999. Geometrical effects in fatigue: a unifying theoretical model. International Journal of Fatigue, Volume 21, pp. 413-420. Taylor, D., 2001. A mechanistic approach to critical-distance methods in notch fatigue. Fatigue & Fracture of Engineering Materials & Structures, Volume 24, pp. 215-224. Taylor, D., 2007. The theory of critical distances : a new perspective in fracture mechanics. London: Elsevier. Taylor, D., Bologna, P. & Bel Knani, K., 2000. Prediction of fatigue failure location on a component using a critical distance method. International Journal of Fatigue, Volume 22, pp. 735-742. Topper, T. H., Wetzel, R. M. & Morrow, J. D., 1969. Neuber’s rule applied to fatigue of notched specimens. Journal of Materials, 4(1), pp. 200 209. Zeng, Z. & Fatemi, A., 2001. Elasto-plastic stress and strain bahaviour at notch roots under monotonic and cyclic loadings. Journal of Strain Analysis for Engineering Design, Volume 36, pp. 287-300. Acknowledgments