Kmax effects on the near-threshold fatigue crack growth of powder-metallurgy aluminum alloys

Fatigue crack growth (FCG) research conducted in the near-threshold regime has identified a room-temperature creep crack growth damage mechanism for a fine-grain powder-metallurgy aluminum alloy (8009). At very low ΔK, an abrupt acceleration in room-temperature FCG rate occurs at high stress ratio and is exacerbated by increased levels of Kmax (Kmax ⩾ 0.4KIc). Detailed crack-surface analysis correlates accelerated FCG with the formation of crack-tip process zone micro-void damage. Experimental results show that the near-threshold and Kmax influenced accelerated crack growth is time and temperature dependent.