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R. Citarella et alii, Frattura ed Integrità Strutturale, 34 (2015) 554-563; DOI: 10.3221/IGF-ESIS.34.61 562 Control factors (matrix L 4 ) Noise factors (matrix L 4 ) Average displacement (mm) S/N ratio (  =-10Log 10 (  (y i 2 )/n ) f e shaft tolerance grade i1 i1 i2 i2 f1 f2 f1 f2 t1 t2 t2 t1 0.2 2.05 n6 1.25E-01 1.15E-01 2.20E-01 3.00E-01 1.90E-01 1.38E+01 0.2 3 p6 8.10E-02 7.90E-02 7.90E-02 1.14E-01 8.83E-02 2.10E+01 0.1 2.05 p6 2.80E-01 2.52E-01 2.59E-01 3.30E-01 2.80E-01 1.10E+01 0.1 3 n6 1.78E-01 1.50E-01 1.90E-01 2.35E-01 1.88E-01 1.44E+01 Table 3 : Maximum shaft-hub tangential displacements (mm) for each of the 16 tested configurations. Control factors (matrix L 4 ) Noise factors (matrix L 4 ) Average hub radial expansion (mm) S/N ratio (  =-10Log 10 (  (y i 2 )/n) ) f e shaft tolerance grade i1 i1 i2 i2 f1 f2 f1 f2 t1 t2 t2 t1 0.2 2.05 n6 3.60E-02 3.27E-02 4.38E-02 5.53E-02 4.20E-02 2.74E+01 0.2 3 p6 4.47E-02 4.45E-02 3.47E-02 4.26E-02 4.16E-02 2.76E+01 0.1 2.05 p6 7.01E-02 6.55E-02 5.84E-02 7.00E-02 6.60E-02 2.36E+01 0.1 3 n6 5.70E-02 5.05E-02 5.06E-02 6.10E-02 5.48E-02 2.52E+01 Table 4 : Maximum hub radial expansion for each of the 16 tested configurations. The identified optimal level assumes the following combination of the control factors: •  = 0.2 since it has a beneficial effect on all the performance parameters with the exception of the press fit force, which increases the mean value; • e = 3 since, while slightly increasing the sensitivity of the stresses to the noises and the press fit force, it determines a beneficial effect on the relative displacements as well as on the radial expansion of the hub; • interference fit H7/n6 since it reduces the stress state (it is worth recalling that stresses due to interference fit cannot be reduced by increasing the hub length), making it less sensitive to noises, even if the relative circumferential slidings increase, determining together with the eccentricity choice, a good compromise at the stress-strain level. This reduces the radial deformation of the hub as well as the press fit force that is already reduced by previous choices. It is evident that if the priority of the designer were the fatigue life of the coupling rather than the static resistance, it would be better to choose the coupling H7/p6, which ensures a better tightening of the coupling, useful in preventing the phenomena of “fretting” (damage due to wear from relative motion under normal load). C ONFIRMATION EXPERIMENT TO VALIDATE THE PROCEDURE t this point, it is possible to verify if the hypothesis of no interaction between the control factors are satisfied. This is achieved by the so-called confirmation experiment that simulates the behaviour of the joint in the identified optimal configuration by simultaneously superimposing noises. The obtained numerical results are then compared with those determined analytically to check their correspondence. If not verified, the assumptions made should be reviewed, resulting in the possible existence of interactions between the control factors or an incorrect setting of the objective functions. The optimum configuration is not present among those already simulated, with it being necessary to A