PSI - Issue 61

Aliyye Kara et al. / Procedia Structural Integrity 61 (2024) 98–107 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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elasto-plastic finite element simulation with a kinematic hardening material model. In time domain analysis, a notched cylindrical specimen subjected to a narrow-band random stress was used as a case study. The kinematic model was calibrated on the Ramberg-Osgood curve used by the spectral method. The comparison between time and frequency domain methods, made in terms of cumulative distribution functions of stress and strain amplitudes, aimed to understand the capability of the spectral method in representing the elasto-plastic material behavior and stress multiaxiality. The results obtained suggest the following conclusions: • the strain amplitude CDFs estimated in both time domain and frequency domain are shifted from the Rayleigh distribution valid for the elastic case, indicating the effect of plasticity. • in the spectral approach, the strain amplitude CDF is continuous. In time-domain results, instead, plasticity determines the presence of a knee point dividing the CDF into two parts with different trends: the left one at lower amplitudes is related to the material elastic response, the right part at larger amplitudes is associated with plasticity, and its portion widens as the amount of plasticity increases. • the strain-based spectral approach using the Neuber’s rule , though being a simple and straightforward approach, applies to the stress amplitude probability distribution (after rainflow counting) while ignoring the actual course of the stress time history, i.e., it is path-independent. Moreover, it assumes a uniaxial analysis, whereas the time domain results have shown that stress multiaxiality plays a role. In conclusion, the strain-based spectral approach based on Neuber’s rule gives slightly different estimations compared to time-domain results with plasticity. The reason may be attributed to the presence of a multiaxial stress state at the notch and to plasticity. It seems reasonable to affirm that the strain- based spectral approach using Neuber’s rule is appropriate for uniaxial stress states, while some caution is suggested in its use with multiaxial stress. Acknowledgements This study is supported by The Scientific and Technological Research Council of Türkiye (TÜBİTAK) under 2214A – International Ph.D. Research Scholarship Program. References Benasciutti, D., Srnec Novak, J., Moro, L., De Bona, F., Stanojević, A. , 2018. Experimental characterisation of a CuAg alloy for thermo‐mechanical applications. Part 1: Identifying parameters of non‐linear plasticity models. Fatigue & Fracture of Engineering Materials & Structures, 41(6), 1364-1377. Böhm, M., Kowalski, M., Niesłony, A., 2020. Influence of the elastoplastic strain on fatigue durability determined with the u se of the spectral method. Materials, 13(2), 423. Dirlik, T., Benasciutti, D., 2021. Dirlik and Tovo-Benasciutti spectral methods in vibration fatigue: a review with a historical perspective. Metals, 11(9), 1333. Rognon, H., Da Silva Botelho, T., Tawfiq, I., Galtier, A., Bennebach, M., 2011. Modeling of plasticity in spectral methods for fatigue damage estimation of narrowband random vibrations, ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. Washington DC, USA, paper DETC2011-48342, pp. 771-779. Rognon, H., Botelho, T. D. S., Tawfiq, I., Bennebach, M., 2014. Spectral methods plasticity modeling for fatigue damage estimation: experimental application – uniaxial case. Mechanics & Industry, 15(3), 233-242. Slavič, J., Boltež ar, M., Mr š nik, M., Č esnik, M., Javh, J., 2020. Vibration Fatigue by Spectral Methods: From Structural Dynamics to Fatigue Damage – Theory and Experiments ” . Elsevier, Oxford, United Kingdom. WAFO group, 2017. WAFO – A Matlab toolbox for analysis of random waves and loads: A tutorial. Centre for Mathematical Sciences, Lund University. Winterstein, S. R., 1985. Non-normal responses and fatigue damage. Journal of Engineering Mechanics, 111(10), 1291-1295. Winterstein, S. R., 1988. Nonlinear vibration models for extremes and fatigue. Journal of Engineering Mechanics, 114(10), 1772-1790.