PSI - Issue 18

A. Vshivkov et al. / Procedia Structural Integrity 18 (2019) 608–615 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The results of this study confirm the hypothesis for the existence of two modes of energy dissipation during the fatigue cracks propagation. The first mode corresponds to slowly propagating cracks (10e-7 – 10e-5 m/cycle) and crack rate is proportional the heat dissipation and crack length. In the second mode there is linear relation between crack rate and heat dissipation. The point corresponding to a change in the character of energy dissipation lies on the linear section of the Paris curve. The obtained experimental results allows us to generalize the hypothesis about the linear relationship between the energy dissipation at the fatigue crack tip and its growth rate to the case of biaxial loading. The study revealed qualitative agreement between the energy approach to the description of the fatigue crack propagation and the classical approach, which is based on the use of the stress intensity factor. To provide an adequate explanation for the observed results, a theoretical analysis was performed in order to study the plastic work at the fatigue crack tip taking into account the evolution of both monotonic and cyclic plastic zones. This analysis allowed us to propose a simple approximation for energy dissipation at the fatigue crack tip. From analysis of experimental and theoretical results, coefficients of this approximation are the same for uniaxial and biaxial loading. The obtained theoretical results give a good qualitative description of the specific features of energy dissipation. Plastic work and, as a consequence, energy dissipation at the crack tip were determined by the crack rate. The theoretical calculation of plastic deformation based on the elastic solution and the secant modulus of elasticity. The heat flux from the crack tip is represented as the sum of two functions describing energy dissipation in monotonic and reversible plastic zones separately. It has been shown that dissipation in a reversible plastic zone is a function of the applied stress amplitude only. Acknowledgements The work was supported by the Russian Science Foundation (grant No. 19-77-30008). Research study of Shlyannikov and Yarullin was done by the financial support from the government assignment for FRC Kazan Scientific Center of RAS. References [1] Yates, J.R., Zanganeh, M., Tomlinson, R.A., Brown, M.W., DiazGarrido F.A., 2008. Crack paths under mixed mode loading. Engineering Fracture Mechanics 75 (3-4), 319-330. [2] Mokhtarishirazabad, M., Lopez-Crespo, P., Moreno, B., Lopez-Moreno, A., Zanganeh M., 2017. Optical and analytical investigation of overloads in biaxial fatigue cracks. International Journal of Fatigue, 100 (2), 583-590. [3] Izumi, Y., Sakagami, T., Yasumura, K., Shiozawa, D., 2014. A new approach for evaluating stress intensity factor based on thermoelastic stress analysis. APCFS/SIF 47-51. [4] Short, J. S., Hoeppner, D. W., 1989. A Global/local theory of fatigue crack propagation. Engineering Fracture mechanics 33 (2), 175-184. [5] Meneghetti, G., Ricotta, M., 2016. Evaluating the heat energy dissipated in a small volume surrounding the tip of a fatigue crack. International Journal of Fatigue 92 (2), 605-615. [6] Risitano, A., Risitano, G., 2013. Cumulative damage evaluation in multiple cycle fatigue tests taking into account energy parameters. International Journal of Fatigue 48, 214-222. [7] Pradere, C., Joanicot, M., Batsale, J-C., Toutain, J., Gourdon, C., 2006. Processing of temperature field in chemical microreactors with infrared thermography. QIRT Journal 3, 117-135. [8] Matvienko, Yu.G., Morozov, E M., 2004. Calculation of the energy J-integral for bodies with notches and cracks. International Journal of Fracture 125, 249-261. [9] Rosakis, P., Rosakis, A.J., Ravichandran, G., Hodowany, J., 2000. A thermodynamic internal variable model for the partitional of plastic work into heat and stored energy in metals. J. Mech. Phys. Solids 48, 581-607. [10] Oliferuk, W., Maj, M., Raniecki, B. (2004). Experimental Analysis of Energy Storage Rate Components during Tensile Deformation of Polycrystals, Materials Science and Engineering, 374, pp. 77-81. [11] Izyumova, A., Plekhov, O., 2014. Calculation of the energy J-integral in plastic zone ahead of a crack tip by infrared scanning. FFEMS 37, 1330–1337. [12] Farren, W.S., Taylor, G.I., 1925. The heat developed during plastic extension of metals. Proc. Royal. Soc. of London. Ser. 107, 422-451. [13] Vshivkov, А., Iziumova, A., Bar, U., Plekhov, O., 2016. Experimental study of heat dissipation at the crack tip during fatigue crack propagation. Fracture and Structural Integrity 35, 131-137.