Transient crack growth behavior in aluminum alloys C415-T8 and 2519-T87

Abstract

This research focused on the creep crack growth characteristics of two creep-brittle aluminum–copper alloys in sheet form, 2519-T87 (2.921 mm) and its chemical variant C415-T8 (2.286 mm), at 135 and 150°C. Transient crack growth behavior during which the creep crack growth rate does not correlate with K was observed in both aluminum alloys. By utilizing a transition time, t g, concept, the data obtained under transient crack growth conditions were separated from the quasi-steady-state crack growth data. In the quasi-steady-state regime, the creep crack growth rates were shown to best correlate with the stress intensity factor, K, for both alloys and test temperatures. The window for steady-state crack growth in creep-brittle materials is demonstrated to be very narrow, and the proposed condition for steady-state crack growth behavior is that V ̇ c / V ̇ ≤0.50 and that V ̇ c / V ̇ changes by less than 100% over a crack extension of 0.5 mm. K/ r q c is investigated as a crack tip parameter applicable to both transient and steady-state crack growth conditions; however, the experimental difficulties in determining the creep zone size were encountered and are discussed in the paper.