Environmentally Assisted Fatigue in the Gaseous Atmosphere

Effect of Frequency, Environment, and Temperature on Fatigue Behavior of E319 Cast-Aluminum Alloy: Small-Crack Propagation

“…On the other hand, fatigue testing at conventional frequencies (approximately 10 to 100 Hz) represents water exposure of approximately 9 to 94 Pa s, which is within, or very close to, the regime of saturated environmental effect. [14] and [15]), compared with experimental data, at a constant DK of 2 MPa ffiffiffiffi m p . Fig.…”

“…It has been observed that the fatigue-crack growth threshold decreased and fatigue-crack growth rate increased in the presence of water vapor in atmospheric air for aluminum alloys. [10][11][12][13][14][15][16][17] Because the duration of crack-tip opening under ultrasonic-frequency loading at 20 kHz is an order of magnitude shorter for each cycle than for conventional fatigue experiments, any environmentally assisted increase in fatigue-crack growth rate is generally presumed to be less pronounced at 20 kHz, leading to lower fatigue-crack growth rate at this frequency. Holper et al [9] studied the influence of frequency on fatiguecrack growth of aluminum alloys and reported that fatigue cracks propagated at lower growth rates at 20 kHz than at 20 Hz in ambient air if cycled above threshold; however, the test frequency had no influence on the fatigue-crack growth threshold itself.…”

Effect of water vapor pressure on fatigue crack growth in Al–Zn–Cu–Mg over wide-range stress intensity factor loading

“…Environment has an equally important impact on da/dN for structural metals [5][6][7][8][9][10]. For precipitation hardened aluminum alloys, loading in moist-gaseous environments enhances da/dN relative to crack growth in ultra-high vacuum, with growth rate increase correlated to the ratio of water vapor pressure (P H2O ) to loading frequency (f ) [6][7][8][9]11].…”

“…Environment has an equally important impact on da/dN for structural metals [5][6][7][8][9][10]. For precipitation hardened aluminum alloys, loading in moist-gaseous environments enhances da/dN relative to crack growth in ultra-high vacuum, with growth rate increase correlated to the ratio of water vapor pressure (P H2O ) to loading frequency (f ) [6][7][8][9]11]. For this class of alloys, da/dN depends on the interaction of K, K max and P H2O /f; the resulting complex crack growth rate law is central to accurate damage tolerant component prognosis [12][13][14] and alloy development [15][16][17].…”

Propagation Lifetime from the Surface and Internal Defects in the Ultra High Cycle Fatigue Regime~!2008-03-10~!2008-05-06~!2008-07-03~!

“…It is necessary to get the crack propagation effective behavior for steels, under air and vacuum. The work of Petit and Henaff [17][18][19] gives us the experimental effective Paris law for steels, under air and vacuum: In Fig. (4), four parameters have to be considered for the discussion of the results : crack shape, stress level and stress gradient, crack closure and environment.…”