ISSN:
1460-2695
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
The deleterious influence of atmospheric moisture on the fatigue properties of an aluminium wrought alloy AlZnMgCu1.5-T6, an aluminium cast alloy AlSi9Cu3 and magnesium cast alloys AM60 hp, AZ91 hp and AS21 hp has been studied at a cycling frequency of 20 kHz. Atmospheric moisture accelerates fatigue crack growth and decreases the threshold stress intensities to 55–75% of the respective values in vacuum. In ambient air, fatigue crack growth rates were up to two decades higher than those in vacuum. Accelerated crack growth was found at propagation rates below about 2 × 10−9 m cycle−1 in aluminium alloys and below about 3 × 10−8 m cycle−1 in magnesium alloys. As the threshold regime is approached, fatigue cracks in ambient air either propagate at a minimum mean growth rate on average of approximately one lattice spacing per cycle or they stop propagating, whereas mean growth rates of 10−12 m cycle−1 were found in vacuum. Crack initiation and slow fatigue crack growth mainly determine lifetimes in the high cycle regime, and endurance data obtained at ultrasonic frequency in ambient air of 40–60% relative humidity are similar to lifetimes measured at conventional frequencies.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1046/j.1460-2695.2002.00571.x
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