PSI - Issue 39

6

Author name / Structural Integrity Procedia 00 (2021) 000–000

Camilla Ronchei et al. / Procedia Structural Integrity 39 (2022) 460–465

465

5. Conclusions In the present research work, the accuracy of the RED criterion in estimating fatigue lifetime of metallic components under non-proportional loading has been discussed. In particular, by following the same philosophy of Borodii criterion, an enhancement factor (function of material constants, strain path orientation and degree of non proportionality) has been implemented in the damage parameter relationship. The accuracy of the present criterion has been verified by considering an experimental campaign performed on plain specimens made of TC4 titanium alloy, which is sensitive to loading non-proportionality and widely used in industry. In particular, fatigue data related to both proportional and non-proportional biaxial tests (combined tension torsion) have been simulated through the RED criterion. Although performing the fatigue lifetime assessment of mechanical components under non-proportional loading is complex, the reliability level of the RED criterion for such a case is satisfactory. As a matter of fact, a good agreement between experimental and theoretical fatigue lifetime is in general observed since the obtained results fall mostly into scatter band 3. However, further investigations on other metallic materials, sensitive to additional cyclic hardening, are needed in order to develop a robust engineering tool suitable for estimating fatigue lifetime in situations of practical interest. Acknowledgements The present research work is supported by Italian Ministry of University and Research (P.R.I.N. National Grant 2017, Project code 2017HFPKZY; University of Parma Research Unit). References Borodii, M., 2001. Obtaining a Low-Cycle Fatigue Strain Criterion. Strength of Materials 33, 217-223. Borodii, M.V., Strizhalo, V.A., 2000. Analysis of the experimental data on a low cycle fatigue under nonproportional straining. International Journal of Fatigue 22, 275-282. Carpinteri, A., Ronchei, C., Scorza, D., Vantadori, S., 2015. Fatigue life estimation for multiaxial low-cycle fatigue regime: the influence of the effective Poisson ratio value. Theoretical and Applied Fracture Mechanics 79, 77-83. Fatemi, A., 1985. Fatigue and Deformation under Proportional and Non-proportional Biaxial Loading. Ph.D. Thesis, University of Iowa, Iowa, USA. Fatemi, A., Socie, D.F., 1988. A critical plane approach to multiaxial fatigue damage including out-of-phase loading. Fatigue & Fracture of Engineering Materials & Structures 11, 149–165. Skibicki, D., 2014. Phenomena and Computational Models of Non-Proportional Fatigue of Materials. Springer Science and Business Media LLC, Berlin/Heidelberg, Germany. Smith, R.N., Watson, P., Topper, T.H., 1970. A stress–strain parameter for the fatigue of metals. Journal of Materials 5, 767–778. Socie, D.F., 1987. Multiaxial fatigue damage models. Journal of Engineering Materials and Technology 109, 293-298. Vantadori, S., 2021. A novel multiaxial strain-based criterion considering additional cyclic hardening. Materials 14, 2542. Wu, Z.R., Hu, X.T., Song, Y.D., 2014. Multiaxial fatigue life prediction for titanium alloy TC4 under proportional and nonproportional loading. International Journal of Fatigue 59, 170–175.