CRACK GROWTH UNDER INTERMITTENT OVERLOADS

L. P. Borrego  J. M. Costa  J. M. Ferreira      

Anales de la Mecánica de la Fractura, nº 21 . 2004 . Pág. -
Ver (.pdf): 6-05-f

Resumen: This study analyses the fatigue crack growth behaviour in AlMgSi1-T6 aluminium alloy due to several loading sequences containing intermittent overloads. The fatigue crack propagation tests have been performed in load control mode using Middle-Tension specimens. Two stress ratios: R=0.05 and R=0.4, and four intermediate baseline cycles: nBL=10, nBL=100, nBL=1000 and nBL=10000, were analysed. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. The observed fatigue crack growth behaviour is compared to constant amplitude loading and discussed in terms of the intermediate baseline cycles and stress ratio. The crack closure parameter U was obtained and compared with the crack growth transients. For less frequently applied overloads crack retardation was observed, while the results for 10 baseline cycles between overloads presented crack acceleration. In spite of some discrepancy, attributed to the quick change of the closure levels, it is clear that plasticity-induced crack closure plays an important role on the load nteraction effects observed in this aluminium alloy.

LocalizaciónPunta Umbría

Department of Mechanical Engineering, Instituto Superior de Engenharia de Coimbra - ISEC, Rua Pedro Nunes, Quinta da Nora, 3030-199 Coimbra, Portugal
Department of Mechanical Engineering, University of Coimbra, Polo II, Pinhal de Marrocos, 3030-201 Coimbra, Portugal
Department of Mechanical Engineering, University of Coimbra, Polo II, Pinhal de Marrocos, 3030-201 Coimbra, Portugal