Spectrum Fatigue Crack Growth Rate Characteristics of Cast Aluminum Alloys A201-T7 and A357-T6

摘要

The spectrum fatigue crack growth characteristics of cast aluminum alloys A201-T7 and A357-T6 were evaluated and compared with wrought aluminum 7050-T76 data. For specimens tested at three different spectrum stress levels, A357-T6 consistently possessed the longest fatigue life, nearly double that of A201-T7 and 7050-T76. At the lowest maximum spectrum stress level tested 7050-T76 had a greater fatigue crack growth life than 7050-T76; at the highest maximum stress level tested 7050-T76 had a greater FCG life than A201-T7. Critical crack size of each alloy at failure varied considerably. Further analysis of the a vs. N record of each sample to obtain the crack growth rate (FCGR) vs. the corresponding stress intensity indicated that A357-T6 had the lowest crack growth rate over the range of stress intensity examined. FCGR comparisons between A201-T7 anf 7050-T76 depended on the level of stress intensity. Macrofractography revealed that the alloys had distinctively different fracture topographies. Microfractography, using scanning electron microscopy, revealed little because compressive loads obliterated features typically associated with fatique.