Issue 30

D. Nappini et alii, Frattura ed Integrità Strutturale, 30 (2014) 394-402; DOI: 10.3221/IGF-ESIS.30.47 398 Experimental procedure Initially, in order to asses a statistical dispersion of indentation response a set of measures was performed on a forging ring piece of ASTM A182F22 in “as is” conditions. A set of 25 indentation measurements were carried out using a maximum load of 1800 N and the maximum indenter penetration depth was measured. Tab. 2 and Fig. 4 respectively show an overview of the obtained values and the related Gaussian distribution, highlighting as the dispersion of indentation response is low. Min Max Aver. St.dev. 112.2 115.9 114.2 1.11 Table 2: Statistical parameters of the indentation response [µm] on a set of 25 measurements. Figure 4: Gaussian curve of indentation response. Aim of the research is to investigate the capability of the instrumented spherical indentation system to evaluate variations in the material properties, due to damage resulting from stresses and temperature fields during long time service. To perform this task, the sites of indentation were chosen considering both the thermal and the mechanical gradients on components, obtained from FEM analysis. For each component, the measurements were performed in order to analyse the whole surface. In particular, points positioned on lines parallel to the direction of the gradients were selected. Also conventional hardness measurements were carried out using the same criteria. Overall 130 spherical indentation and 50 conventional hardness measurements were performed in order to map the significant areas on the components. Fig. 5a clarify the scheme of spherical indentation of the 1 st stage turbine disc, underlining where sets of measure were carried out. Fig. 5b shows the dimensionless temperature profile obtained for an average engine running in ISO condition for, while fig. 5c shows the results of the 2D axial-symmetric elastic analysis at steady state condition. Figure 5 : a) Positions of spherical indentation (red points) on item. In the yellow points are carried out conventional Brinnel tests b) Positions of spherical indentation (black points) overlying on thermal analysis c) Positions of spherical indentation overlying on structural analysis. 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 111 112 113 114 115 116 117 Gaussian distribution [1/μm] Max indenter penetration [μm] a) b) c)