Aluminum alloys crack-growth rates

Fig. 7.112 Dependence of corrosion-crack-growth rate on stress intensity for two high-strength aluminum alloys in saturated NaCI solution at 23 °C. Crack orientation TL (stress in transverse direction crack propagation in longitudinal direction). Source Ref 159...

Fig. 7.114 Dependence of stress-corrosion-crack-growth rate on stress intensity for a high-strength aluminum alloy at various temperatures. Source Ref 1 59...

Fie. 7.125 Corrosion-fatigue-crack-growth rate as a function of stress-in-tensity range for a high-strength aluminum alloy in dry argon and indicated halide solutions. Source Ref 1 73... 

Figure 9.2. Influence of water vapor pressure (or pressure/frequency) on fatigue crack growth rates in 2219-T851 aluminum alloy at room temperature. Solid line represents model predictions [2].

Figure 9.6. The influence of water vapor pressure on fatigue crack growth rate in I/M 7075-T651 aluminum alloy at room temperature [5].

The fatigue crack growth rate test results on AMg6 aluminum alloy at 4 K, 76 K, and room temperature, are summarized in Figs. 3,4, and 5, respectively. The Paris power law [ ] is used as the basis for empirical analysis of the data... 

The fatigue crack growth rates and the fracture toughness of AMg6 aluminum alloy have been determined at room temperature, 76 K, and 4K. The results indicate that ... 

Fig. 1.76 Crack growth rates obtained by Lankford on aluminum alloy 7075-T651 [118, 119]...

SCC development depends on both the duration and magnitude of applied tensile stress. Fracture mechanics tools for the determination of crack growth rates are commonly used in the evaluation of SCC resistance for aluminum alloys [90]. Such tests suggest a minimum (threshold) stress intensity that is required for cracking to develop. 

Effect of StrcM. Whether or not SCC develops in a susceptible aluminum alloy product depends on both magnitude and duration of tensile strength acting at the surface. The effects of the factors have been established most commonly by means of acederated labo-ratoty tests results of one set of such tests are reflected in the shaded and cross-hatched bands in Fig. 4. Despite introduction of fracture mechanics techniques capable of determining crack growth rates, such tests... 

Pa are comparable with those obtained in air (at 40 to 60 percent relative humidity), distilled water, and 3.5 percent NaCl solution [1]. The data in dehumidified argon correspond to those in vacuum at less than 0.50 /uPa. These data are also shown in Fig. 9.2 as a function of water vapor pressure at three AK levels. The error bands represent ninety-five percent confidence intervals computed from the residual standard deviations in each set of data. The results in Fig. 9.2 show that at a frequency of 5 Hz, the rate of crack growth is essentially unaffected by water vapor until a threshold pressure is reached. (This threshold pressure is attributable to the significant transport limitation at these very low water vapor pressures.) The rate then increased and reached a maximum within one order of magnitude increase in vapor pressure from this threshold. The maximum rate is equal to that obtained in air, distilled water, and 3.5 percent NaCl solution (at 20 Hz). The transition range, in terms of pressure/frequency, is comparable to that reported by Bradshaw and Wheeler [9] on another aluminum alloy. 

Figure 37 The effect of crack tip strain rate, via loading rate, on crack growth in a high-strength aluminum alloy [54,158], (Courtesy of NACE.)...

Equation (4.64) shows a straight line relationship between (da/dN) and AK, with slope n and intercepts C. Region B shows the steady-state rate of crack growth. The value of n is 3 for steels and in the range of 3-4 for aluminum alloys. 

Liu et al. (2002) studied the influence of different inhibitors on the fatigue propagation crack rate in high strength aluminum alloy AA7075-T76, in a 3.5% NaCl solution These authors observed, in the presence of phosphate, molybdate, citrate or thiazole/imidazole, a reduction in the rate of crack growth, mainly in the first stages of its propa tion, as a consequence of the diverse mechaiusms of inhibition of each of the used compounds. 

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