13 Determination of Mixed-Mode (I/III) Fracture of Polycarbonate 81 Fig. 13.6 Mixed-Mode fracture experimental setup using PC specimen in a uniaxial tension-torsion machine, β=67.5◦ Fig. 13.7 Torque vs rotation angle for a spiral v-notch specimen up to fracture, β=67.5◦ 13.3.3 Numerical Computation of SIFs and J-Integral The fracture load is used as input to the numerical model for calculation of the J-integral and the stress intensity factors for Mode-I, Mode-III and Mixed-Mode (I/III) loading conditions. The theoretical solution of the spirally notched specimen using a 3D interacting integral method is available in previous work [21, 22]. As shown in Fig. 13.8, there is sufficient fracture load to generate brittle fracture at the notch front with a small jump just prior to fracture initiation moment. In general, fracture occurs under nominally plane strain conditions. From Fig. 13.8 and Table 13.2, the fracture toughness of the PC specimen under Mixed-Mode conditions indicates that KIc >KIIIc for β =67.5◦, with the in-plane Mode-II component near zero [23]. Finally, the total Mixed-Mode (I/III) fracture toughness of PC, given by Eq. (13.1), is higher than the fracture toughness of Mode-I, i.e. K(I/III)c >KIc: KI/IIIc = K 2 I + K 2 III 1−ν (13.1)
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