Issue 30

D. Nappini et alii, Frattura ed Integrità Strutturale, 30 (2014) 394-402; DOI: 10.3221/IGF-ESIS.30.47 401 Indentation sites at the same temperature performed on the rotor components were considered equivalent points of measure and the resulting average values were reported in function of temperature. The most significant parameters related to temperature damaging are the elastic unloading contact stiffness and the area included by loading and unloading curve. These variables showed a linear behaviour with the temperature; after a calibration step, indentation tests may be used as an index of the average temperature acting on the component. So, these parameters are also promising indicators to material damage due to extensive service. The stress acting on components was considered an amplification factor of the temperature field. Using the linear factor σ / σ max an improvement of the correlation was obtained. The correlations proposed should be clearly verified with other tests. In fact, it is obviously that the performed study is still far from obtaining an analytical relation between a parameter, derived from the indentation test, and damage of the component; however, it demonstrates the feasibility of this task. R EFERENCES [1] Dowson, P., Dowson, J., Remaining Life assessment technology applied to steam turbines and hot gas expanders, ASME Proceedings, Structures and Dynamics, paper No. GT2011-45324, (2011) 47-61. [2] Viswanathan, R., Damage mechanisms and life assessment of high temperature components, ASM International, Metals Park, (1989). [3] De Prosperis, R., Di Sisto, P., Borkowski M., Gas turbine life prediction and optimization device and method, patent WO 2013014202 A1, Nuovo Pignone Spa [IT], (2013). [4] Fujiyama, K., Fujiwara, T., Damage in high temperature components and the life assessment technologies, ICF10, Honolulu, (2001). [5] Cheng, Y.T., Page, T., Pharr, G.M., Swain, M., Wahl, K.J. (eds.), Fundamental and Applications of Instrumented Indentation in Multidisciplinary Research, Journal of Material Research, 19 (2004). [6] Baker, S.P., Cook, R.F., Corcoran, S.G., Moody, N.R., Fundamentals of Nanoindentation and Nanotribology II, Materials Research Society Symposium Proceedings, Vol. 649 (2001). [7] Van Landingham, M.R., Review of instrumented indentation, Journal of Research of the National Institute of Standards and Technology, 108 (4) (2003) 249-265. [8] Fischer-Cripps, A.C., Critical Review of analysis and interpretation of nanoindentation test data, Surface & Coatings Technology, 200 (14-15) (2006) 4153-4165. [9] Li, X., Bhushan, B., A review of nanoindentation continuous stiffness measurement technique and its applications, Materials Characterization, 48 (1) (2002) 11–36. [10] Li, J., Li, F., He, M., Xue, F., Zhang, M., Wang, C., Indentation technique for estimating the fracture toughness of 7050 aluminum alloy with the Berkovich indenter, Materials and Design, 40 (2012) 176–184. [11] Oliver, W.C., Pharr, G.M., Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology, Journal of Materials Research, 19 (1) (2004) 3-20. [12] Nayebi, A., El Abdi, R., Bartier, O., Mauvoisin, G., New procedure to determine steel mechanical parameters from the spherical indentation technique, Mech. Mater. 34 (4), (2002) 243-254. [13] Moussa, C., Bartier, O., Mauvoisin, G., Pilvin, P. , Delattre, G., Characterization of homogeneous and plastically graded materials with spherical indentation and inverse analysis, Journal of Materials Research 27 (1) (2012) 20-27. [14] Lee, J.H., Kim, T., Lee, H., A study on robust indentation techniques to evaluate elastic-plastic properties of metals. Int. J Solids Struct. 47 (2010) 647-664. [15] Chicot, D., Gil, L., Silva, K., Roudet, F., Puchi-Cabrera, E.S., Staia, M.H., Teer, D.G., Thin film hardness determination using indentation loading curve modelling, Thin Solids Films, 518, (2010) 5565-5571. [16] Zhang, M., Li, F., Yuan, Z., Li, J., Wang, S., Effect of heat treatment on the micro-indentation behavior of powder metallurgy nickel based superalloy FGH96, Materials & Design, 49 (2013) 705–715. [17] Di Gioia, A., Progetto Costruttivo di un Indentatore Sferico Strumentato”, Bachelor’s Degree Dissertation, University of Pisa, Faculty of Engineering, Pisa, (2005). [18] Beghini, M., Bertini, L., Fontanari, V., Evaluation of the stress–strain curve of metallic materials by spherical indentation, International Journal of Solids and Structures, 43 (7-8) (2006) 2441–2459. [19] Beghini, M., Bertini, L., Fontanari, V., Mechanical characterization of metallic materials by instrumented spherical indentation, Proceedings of SEM Annual Conference & Exposition on Experimental & Applied Mechanics, (2009) 1- 10.