An evaluation of Delta K-eff estimation procedures on 6061-T6 and 2024-T3 aluminum alloys

Experimental and analytical evidence indicates that 'closure' or interferen ce of crack faces does not entirely isolate the crack tip from damaging str ains due to cyclic loading. Therefore, an estimation of the effective stres s intensity range at the crack tip, Delta K-eff should take into account th e additional cyclic crack tip strain below the opening load. In this invest igation, the estimation of Delta K-eff is based on the traditional opening load method and also on numerous new methods that show improved correlation of fatigue crack growth rate stress ratio effects in general but mostly at near-threshold growth rates. The experimental results of this study also i ndicate that the fatigue crack growth rate is not determined solely by Delt a K-eff but also depends on K-max. A procedure for determining an intrinsic crack growth rate curve is described. (C) 1999 Elsevier Science Ltd. All r ights reserved.