The theory of stress corrosion for slow crack propagation is reviewed in the light of classical Griffith theory of fracture. Experimental data for stress corrosion cracking for glasses, ceramics, and metals are reviewed. We suggest that stress corrosion cracking plays an important role in the intrusion of magmas and in the transport of magmas upward through the lithosphere. It is shown that the effect of decreasing temperature (at progressively shallower levels along the geotherm) would be to decrease the crack velocity by several orders of magnitude if other factors were equal. We also propose that stress corrosion may be an important process in time-dependent earthquake phenomena such as premonitory behavior and earthquake aftershocks. We suggest that slow cracking in the earth is not seismically detectable but may nevertheless precede the terminal (catastrophic) phase of the fracture that is discerned as an earthquake. The seismically quiet periods before some earthquakes and the seismically quiet regions beneath some volcanoes may in fact be regimes of slow crack propagation. Slow crack propagation in a lithospheric plate may provide access routes for magmas which give rise to prominent linear volcanic chains.

Stress corrosion theory of crack propagation with applications to geophysics

Stress corrosion cracking of aluminum alloys is reviewed. An extensive failure analysis shows how many service failures occurred in the aerospace industry over a ten year period and what kind of alloys and stresses led to initiation and propagation of stress corrosion cracks which caused these service failures. The paper contains most of the results of stress corrosion tests with aluminum alloys that have been obtained to date with fracture mechanics techniques. Stress corrosion crack growth rate measurements are compared with the results from smooth specimen testing and it is shown that the correlation between the different test results is very satisfactory. The present and limited status of theoretical understanding of stress corrosion cracking is outlined. A major part of the paper is devoted to the results of the latest alloy development. High strength aluminum alloys of dramatically increased stress corrosion resistance are available now. In the near future, stress corrosion resistant alloys of even higher strength might become available. What is still lacking is a detailed understanding of the mechanisms by which stress corrosion cracks initiate and propagate.

Stress corrosion cracking of aluminum alloys

The corrosion and stress corrosion cracking (SCC) susceptibility of an Al-Mg alloy, AA5083, has been shown to depend on the precipitation of the Mg-rich β phase, (Al3Mg2), but not the enrichment of elemental Mg at grain boundaries to an enrichment ratio of 1.4. These results were determined by measuring the progress of Mg enrichment at grain boundaries, for increasing thermal-treatment times, using auger electron spectroscopy (AES) of grain boundaries exposed by fracture within the spectrometer and by analytical electron microscopy (AEM) of thin foils. The progress of the β phase precipitation was followed by AEM and scanning electron microscopy (SEM), for the same thermal-treatment times. The lack of a Mg-segregation effect on SCC was demonstrated by results obtained with X-ray photoelectron spectroscopy (XPS) analysis of Mg-implanted Al following in-situ electrochemical tests and SCC tests, while the dominance of β phase precipitation was demonstrated by electrochemical analysis and SCC testing. Crack-growth tests of alloy AA5083 demonstrated faster cracking at potentials anodic to the open circuit potential (OCP) with no increase at potentials cathodic to the OCP.

Role of Mg in the stress corrosion cracking of an Al-Mg alloy

Stress corrosion cracking behaviour of 7xxx aluminum alloys: A literature review

: Two important advances over the past 40 years enable the optimization and management of the structural integrity of components in high performance applications. First, the solid mechanics conununity established linear elastic fracture mechanics as the premier framework for modeling the damage tolerance of fracture critical components (Irwin and Wells, 1997; Paris, 1998). Second, materials scientists developed metals with outstanding balances of high tensile strength and high fracture toughness (Garrison, 1990; Wells, 1993; Boyer, 1993; Starke and Staley, 1995; Olson, 1997; Kolts, 1996). An example of achievable strength-toughness properties is provided in Fig. 1, a plot of plane strain fracture toughness vs. tensile yield strength (sigma-YS) for ultra-high strength steels (UHSS) and beta-Ti alloys precipitation hardened with a phase (Gangloff 2001). New nano-scale characterization and high performance computational methods provide for additional advances in the mechanical performance properties of structural metals. These modem alloys and analysis tools satisfy technological needs for optimization and management of component performance in demanding fatigue and fracture critical applications in the aerospace, marine, energy, transportation, and defense sectors.

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Hydrogen Assisted Cracking of High Strength Alloys

High-strength aluminum alloys are of considerable importance in our technologically advanced society Perhaps the best-known application is in the aerospace industry, where the high-strength aluminum alloys are the engineer’s mainstay for rockets, spacecraft, aircraft, and hydrospace vehicles Table 1 lists the chemical compositions for the commonly used high-strength aluminum-base alloys Composition limits for several of these alloys are shown in Fig 1 Typical applications for each of these alloys are listed in Table 2 The heat treatments for the various tempers of these alloys are given in Table 3 Mechanical properties of the alloys are listed in Table 4 (Data in Tables 1–4 were obtained from Refs 1–45a) The highest-strength aluminum alloys are those based on the Al-Cu-Mg (2000 series) and Al-Zn-Mg-Cu (7000 series) alloy systems Since these alloys are the most widely used for today’s high-performance structures, this chapter will concentrate on them

Markus O. Speidel

Papers

Stress-Corrosion Cracking of High-Strength Aluminum Alloys