Corrosion fatigue occurs. Corrosion FatigueCorrosion fatigue is mechanical degradation of a combined effect of corrosion and fatigue under a dynamic or cyclic stress, usually is environmentally assisted into a material. Corrosion fatigue cracks are frequently instigated at the surface, and sub-surface cracks begin at areas of stress concentration where material defects are located near the surface. Corrosion fatigue cracks are characteristically transgranular with a small region denoted and some are similar to the fatigue mechanism, where corrosion fatigue cracking is frequently characterized by striation patterns (shown in Figure 11), which are perpendicular to the crack propagation direction. The final stage of failure occurrence of the material is purely a mechanical degradation with no intervention from corrosion and becomes exactly the similar mechanism of fatigue failure.Corrosion fatigue is a possible cause for the failure modes of a number of types of metals and alloys in different types of environments. Decrease in fatigue strength due to corrosion fatigue is influenced by the effects of degradation from corrosive environment. In a corrosive environment crack growth rate may have higher rates than in a non corrosive environment, as result can shortened the fatigue life-cycle of a material exposed to a corrosion and fatigue mechanism simultaneously.There are several factors that influence growth rate of corrosion fatigue. These are as follow: Corrosion damage, e.g. pitting origins stress raisers in the materials surrounding area of the pit, similar to notch effects. As this drives to crack initiation at a stress below that a material in a non-corrosive conditions. As soon as corrosive elements go into crack, then crack propagates at faster rate. Temperature; Metal composition, strength and fracture toughness Strength and fracture toughness are important material properties when taking into consideration for how to control/protect against corrosion fatigue.

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