Elevated temperature fracture toughness of Al-Cu-Mg-Ag sheet: Characterization and modeling
- Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering
The plane-strain initiation fracture toughness (K{sub JlCi}) and plane-stress crack growth resistance of two Al-Cu-Mg-Ag alloy sheets are characterized as a function of temperature by a J-integral method. For AA2519 + Mg + Ag, K{sub JlCi} decreases from 32.5 MPa {radical}m at 250 C to 28.5 MPa {radical}m at 175 C, while K{sub JlCi} for a lower Cu variant increases from 34.2 MPa {radical}m at 25 C to 36.0 Mpa {radical}m at 150 C. Crack-tip damage in AA2519 + Mg + Ag evolves by nucleation and growth of voids from large undissolved Al{sub 2}Cu particles, but fracture resistance is controlled by void sheeting coalescence associated with dispersoids. Quantitative fractography, three-dimensional (3-D) reconstruction of fracture surfaces, and metallographic crack profiles indicate that void sheeting is retarded as temperature increases from 25 C to 150 C, consistent with a rising fracture resistance. Primary microvoids nucleate from smaller constituent particles in the low Cu alloy, and fracture strain increases. A strain-controlled micromechanical model accurately predicts K{sub JlCi} as a function of temperature, but includes a critical distance parameter (l*) that is not definable a priori. Nearly constant initiation toughness for AA2519 + Mg + Ag is due to rising fracture strain with temperature, which balances the effects of decreasing flow strength, work hardening, and elastic modulus on the crack-tip strain distribution. Ambient temperature toughnesses of the low Cu variant are comparable to those of AA2519 + Mg + Ag, despite increased fracture strain, because of reduced constituent spacing and l*.
- Sponsoring Organization:
- National Aeronautics and Space Administration, Washington, DC (United States)
- OSTI ID:
- 544057
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 28, Issue 9; Other Information: PBD: Sep 1997
- Country of Publication:
- United States
- Language:
- English
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