Corrosion fatigue is the combination of dynamic loading fatigue crack propagation exacerbated by a stress corrosion cracking (SCC) component which accelerates the cracking process. This type of damage is common in aluminum and steels in contact with salt water, and is a common occurrence in aircraft structures. Because the chlorine ions act as catalysts in the corrosion process, intermittent exposure to even trace amounts of salt can rapidly accelerate fatigue cracking. Corrosion fatigue can occur in combinations of material and environmental stress wherever stress corrosion cracking would also be a possibility, such as austenitic nuclear system components and welds. One of the most damaging aspects is that the corrosive component eliminates the fatigue endurance limit. The corrosive damage component depends upon time rather than stress cycles, and effectively eliminates any safe stress level for infinite life. The S/N curve for an alloy in corrosion fatigue diminishes continuously with increasing cycles.
Introducing a deep stable layer of compression by low plasticity burnishing (LPB®) or controlled plasticity burnishing (CPB) eliminates the stress corrosion component in all alloys investigated to date, including structural aluminums such as 7075-T6, high strength aircraft steels including 300M, and austenitic AISI 304 stainless steel widely used in nuclear applications. A millimeter of high compression introduced with low cold work holds the surface layer below the tensile threshold for stress corrosion cracking, thereby eliminating the cyclic stress corrosion cracking component that accelerates fatigue failures in the aggressive environment.
To learn how designed residual compression can combat corrosion, please call 1-800-883-0851 or email us.