PSI - Issue 28

Rui F. Martins et al. / Procedia Structural Integrity 28 (2020) 74–83 Author name / Structural Integrity Procedia 00 (2020) 000–000

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concerned. Specifically, it was noticed higher stress intensity factor values with increasing torque applied and a decrease of the stress intensity factors with the increase of the thickness of the specimens. Hence, considering the maximum equivalent stress intensity values, K eq MPa.m 0.5 , calculated for each specimen’s thickness (B, in mm), crack length (a/L), and applied torque (T, in N.m), several polynomial functions (Eq. 3) (Table 2) and surface response functions were determined. Moreover, to determine the p ij coefficients of Eq. 3, for the considered torques, a quadratic polynomial equation was fitted, and p i coefficients were calculated (Eq. 4) (Table 2). � � � �� � �� . � � � �� . � �� . � � � � �� . � �. � �� . � � �� . � � � � �� . � � � . � �� . � �. � � �� . � � �� . � � � � �� . � � � . � �� . � � � . � � �� . � �. � �� � � � � . � � � . � � (4) (3)

Fig. 6. Stress intensity factors, K I , K II , K III and K eq , at the lower crack tip (-70º) of a CT specimen with a thickness, B, equal to 2.5 mm and under an applied torque of 6 N.m.

Therefore, by using a two-step procedure (Eqs. 4 and 3), it was possible to determine the stress intensity factor values of the CT specimens under study, having into account the thickness range (2.5-10 mm), and the torsional loads considered (6 ; 7.5 ; 9 ).