PSI - Issue 7

Y. Nadot et al. / Procedia Structural Integrity 7 (2017) 530–535 NADOT Yves / Structural Integrity Procedia 00 (2017) 000–000

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plastic strain applied during the cold working. After several tests, the strain percentage is chosen equal to 12% to manufacture the targeted grain size for this study. Fig. 1 shows the microstructure obtained in accordance with the level of plastic strain applied, 12%. The new average grain diameter is 340 µ m in every direction. The homogeneity of grain size has been checked with a quantification of a ‘‘pseudo” standard deviation of grain size distribution: it is 15 µ m for fine microstructure (grain diameter D g = 30 µ m) and it is 150 µ m for coarse microstructure (D g = 340 µ m). It is of the same order of magnitude in the longitudinal and transverse cutting for two microstructures. As regards the influence of grain diameter on monotonic mechanical properties, Young’s modulus does not change, whereas tensile strength and mostly yield strength decrease notably when grain diameter grows.

Fig. 1. (a-b) fine microstructure (c-d) coarse microstructure / S-N curves (R = -1, 10 Hz, force controlled, Sinus).

Table 1. dimension of defects machined by EDM