Issue34

E. Marcisz et alii, Frattura ed Integrità Strutturale, 34 (2015) 379-386; DOI: 10.3221/IGF-ESIS.34.42 385 Figure 10 : Fatigue crack path of the aluminium alloy 2024. A sample development of crack paths at controlled energy parameter is shown in Fig. 11. Fig. 11a presents crack path observed at energy parameter W a = 0.4 MJ/m 3 ; the specimen was damaged after 11550 cycles. Fig. 11b shows crack path for a specimen examined at energy parameter value W a = 0.35 MJ/m 3 ; the specimen was damaged after 88900 cycles. A sample development of crack paths under bending moment control is illustrated in Fig. 12. Crack path in Fig. 12a was observed at stress value  a = 255 MPa, which according to linear-elastic model corresponds to energy parameter W a = 0.42 MJ/m 3 ; the specimen was damaged after 50300 cycles. Fig. 12b shows crack path obtained during tests for stress  a = 233 MPa. According to linear-elastic model, it corresponds to energy parameter W a = 0.36 MJ/m 3 . The specimen was damaged after 70800 cycles. Presented photos allow observing that crack paths in Figs. 11a and 12a develop in much the same way. Greatest changes in crack path development directions (zigzag) were observed during tests at controlled bending moment amplitude  a = 233 MPa (Fig. 12.b). In case of controlled energy parameter and bending moment the specimens had different cracking courses. After initiation, cracks develop along different planes, where the plane of highest shearing stress is prevailing. a b Figure 11 : Fatigue crack path for controlled amplitude of the energy parameter a b Figure 12 : Fatigue crack path for controlled amplitude of the bending moment.