In an exploratory program for the development of damage tolerant materials for aircraft and helicopter structures, it has been found that laminated panels composed of mill-annealed Ti-6A1-4V sheet and alclad 2024-T3 sheet provided unusual fatigue and fracture resistance. Lamination of these two materials by explosive bonding results in a damage-tolerant fatigue resistant laminate.

Notched-beam specimens were fatigue cycled in pure bending at 30 Hz. The value of stress intensity factor range for crack propagation rates of 2.54 × 10^-9 m/cycle (10^-7 in./cycle) or less appears to be about 17.5 MN/m^3/2 (16 ksiin.) For values of ΔK less than 35 MN/m^3/2 (32 ksiin.) the fatigue crack propagation rate measured in the laminate is smaller than that of either the aluminum alloy or the titanium alloy. Room temperature fracture toughness tests of fatigue precracked beams made of equal thickness layers of the two materials give values higher than those of the component alloys. An interlaminar shear strength of 99 MN/m² (14.3 ksi) was measured.

While complete evaluation of this laminate will require extensive testing, the early indications are that the damage tolerance is superior to that of either of the component metals because of the energy absorbing capacity provided by the laminated construction. Crack growth is retarded by the ductile cladding which forms the welded interfaces, and impact energy is absorbed in deformation and delamination. Moreover, because of favorable residual stresses the laminate appears to have a higher threshold for fatigue crack propagation than either of the component metals. This permits a larger defect size to be sustained without fatigue crack propagation at a given stress level, or a higher stress level to be endured with a given defect size.