PSI - Issue 13

Daniele Rigon et al. / Procedia Structural Integrity 13 (2018) 1638–1643 D. Rigon et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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3. Conclusions In this contribution, the specific heat loss per cycle (Q parameter) was experimentally evaluated for the first time on cold drawn AISI 304L specimens subjected to multiaxial cyclic loads. A cantilever fatigue test bench, consisting of two servo-hydraulic actuators, was adopted for carrying out force-controlled, completely reversed pure bending, pure torsion and combined bending-torsion fatigue tests. Regarding the multiaxial fatigue tests, two phase-shift angles (  = 0°/ 90°) and two different biaxiality ratios ( Λ =1 and 3 ) were analysed. For comparison purposes, force controlled axial, torsional and combined axial-torsional (  = 0°/ 90°, Λ= 3 ) completely reversed fatigue tests were also carried out on thin-walled specimens. After having measured the specific heat loss during individual fatigue tests, it was noted that after approximately one third of the total fatigue life the Q parameter achieves a stationary value, which remains constant during the residual fatigue life. This has been observed both in the uniaxial and multiaxial fatigue tests performed in this contribution. All fatigue test results have been summarised in terms of specific heat loss taken at half the total fatigue life versus the number of cycles to failure and have been compared with the scatter band previously calibrated on push-pull, uniaxial fatigue tests on plain and notched AISI 304L specimens. As expected, pure bending, axial and torsional fatigue data resulted in good agreement with the existing scatter band. In the LCF regime, a good agreement with the scatter band was found for all multiaxial fatigue results obtained from the type (a) specimens. The same cannot be generalized for the type (b) specimens due to the limited data available up to now. Conversely, fatigue results obtained from out-of-phase multiaxial loading conditions with Λ= 1 and 3 as well as in- phase multiaxial with Λ= 3 fall below the previously calibrated scatter band. The present results suggest that for the present material the specific heat loss per cycle can be adopted for multiaxial stress states in the LCF regimes. Finally, additional experimental fatigue tests should be carried out in order to statistically quantify the effects of the biaxiality ratio and the phase-shift on the specific heat loss parameter. Acknowledgements This work was carried out as a part of the project CODE CPDA145872 of the University of Padova. The Authors would like to express their gratitude for financial support. The authors would like to thank also Prof. M. Quaresimin of the Department of Management and Engineering (University of Padova), where the fatigue tests on type (b) specimens were carried out. References Atzori, B., Berto, F., Lazzarin, P., Quaresimin, M., ( 2006 ) . Multi-axial fatigue behaviour of a severely notched carbon steel. International Journal of Fatigue 28, 485 – 493. Ellyin, F., (1997). Fatigue damage, crack growth, and life prediction. Chapman & Hall. Kaleta, J., Blotny, R., Harig, H., (1991). Energy Stored in a Specimen under Fatigue Limit Loading Conditions. Journal of Testing and Evaluation 19, 326 – 333. Lazzarin, P., Livieri, P., Berto, F., Zappalorto, M., (2008). Local strain energy density and fatigue strength of welded joints under uniaxial and multiaxial loading. Engineering Fracture Mechanics 75, 1875 – 1889. Lazzarin, P., Sonsino, C.M., Zambardi, R., (2004). A notch stress intensity approach to assess the multiaxial fatigue strength of welded tube-to flange joints subjected to combined loadings. Fatigue and Fracture of Engineering Materials and Structures 27, 127 – 140. Meneghetti, G., (2007). Analysis of the fatigue strength of a stainless steel based on the energy dissipation. International Journal of Fatigue 29, 81 – 94. Meneghetti, G., Ricotta, M., (2012). The use of the specific heat loss to analyse the low- and high-cycle fatigue behaviour of plain and notched specimens made of a stainless steel. Engineering Fracture Mechanics 81, 2 – 16. Meneghetti, G., Ricotta, M., Atzori, B., (2016). the heat energy dissipated in a control volume to correlate the fatigue strength of bluntly and severely notched stainless steel specimens, in: Proceedings of the 21st European Conference on Fracture, ECF21. Catania, Italy. pp. 2076 – 2083. Meneghetti, G., Ricotta, M., Atzori, B., (2013). A synthesis of the push-pull fatigue behaviour of plain and notched stainless steel specimens by using the specific heat loss. Fatigue and Fracture of Engineering Materials and Structures 36, 1306 – 1322. Meneghetti, G., Ricotta, M., Negrisolo, L., Atzori, B., (2013). A synthesis of the fatigue behavior of stainless steel bars under fully reversed axial or torsion loading by using the specific heat loss. Key Engineering Materials 577 – 578, 453 – 456. Rigon, D., Ricotta, M., Meneghetti, G., (2017). An analysis of the specific heat loss at the tip of severely notched stainless steel specimens to correlate the fatigue strength. Theoretical and Applied Fracture Mechanics 92, 240 – 251.