Mj. Haynes et Rp. Gangloff, ELEVATED-TEMPERATURE FRACTURE-TOUGHNESS OF AL-CU-MG-AG SHEET - CHARACTERIZATION AND MODELING, Metallurgical and materials transactions. A, Physical metallurgy andmaterials science, 28(9), 1997, pp. 1815-1829
The plane-strain initiation fracture toughness (K-JICi) and plane-stre
ss crack growth resistance of two Al-Cu-Mg-Ag alloy sheets are charact
erized as a function of temperature by a J-integral method. For AA2519
+ Mg + Ag, K-JICi, decreases from 32.5 MPa root m at 25 degrees C to
28.5 MPa root m at 175 degrees C while K-JICi for a lower Cu variant i
ncreases from 34.2 MPa root m at 25 degrees C to 36.0 MPa root m at 15
0 degrees C. Crack-tip damage in AA2519 + Mg + Ag evolves by nucleatio
n and growth of voids from large undissolved Al2Cu particles, but frac
ture resistance is controlled by void sheeting coalescence associated
with dispersoids. Quantitative fractography, three-dimensional (3-D) r
econstruction of fracture surfaces, and metallographic crack profiles
indicate that void sheeting is retarded as temperature increases from
25 degrees C to 150 degrees C, consistent with a rising fracture resis
tance. Primary microvoids nucleate from smaller;constituent particles
in the low Cu alloy, and fracture strain increases. A strain-controlle
d micromechanical model accurately predicts K-JICi as a function of te
mperature, 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 bala
nces the effects of decreasing flow strength, work hardening, and elas
tic 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 constit
uent spacing and l.