Crack Growth in Mercury Embrittled Aluminum Alloys under Cyclic and Static Loading Conditions.

摘要

Crack growth rates were measured on three aluminum alloys under cyclic and static loading conditions in laboratory air and in liquid mercury at about +25 deg C. One alloy, 6061-T651, was tested under both loading conditions at temperatures ranging from -25 deg C to +45 deg C. Fracture mechanics techniques were used. Under cyclic loading conditions, no enhanced crack growth in mercury was measured until a critical stress intensity factor range (Delta K) was exceeded. When Delta K increased above the threshold value, the crack growth rae increased by as much as three orders of magnitude, when compared to the crack growth rate in air. From the appearance of the fracture surface the mechanism of embrittlement was deduced to be reduced cohesion. Under static loading conditions, crack velocities of centimeters per second were measured in load control. Under displacement control much slower crack velocities were measured in tow alloys. The decrease in crack velocity was attributed to crack blunting and large plastic zones. Static crack velocity and cyclic crack growth rate increased with decreasing temperature. This unusual temperature effect was related to the kinetics of adsorption of mercury on aluminum. (Author)