Fatigue damage accumulation: the role of corrosion on the early stages of crack development

Abstract

It is now recognised that a complex load history may lead to structural damage that cannot be predicted on the basis of simple uniaxial loading conditions. The application of a single overload can induce sufficient crack growth such that the fatigue limit of a material is compromised. In a similar manner, it is possible to transgress the fatigue limit of a material by applying a number of corrosion cycles which lead to an increase in the size of the defect(s) present in the material beyond that of a 'threshold condition'. Damage accumulation within materials arises owing to the load and environmental history experienced throughout the lifetime of a component or structure. Furthermore, damage owing to load or environment in isolation impacts less on the durability of a structure/component, compared with that when conjoint effects of load and environment are experienced. This paper discusses the contribution that arises from environmental processes, such as corrosion, to final material failure. Synergy owing to corrosion and static/cyclic stress are discussed for both passive (stainless steel) and active (carbon steel) materials.

Influence of Pitting Corrosion on Fatigue and Corrosion Fatigue of Ship and Offshore Structures, Part II: Load - Pit - Crack Interaction

“…In established time periods, the mechanical damage degree was increasing along with increasing number of deformation cycles resulting from increasing load frequency (f). Akid et al stated that the pit initiation period ti has been independent on the frequency f. The present author has reanalyzed the data read from an appropriate diagram published in [25] and stated that a weak relationship did occur and the period ti may be considered approximately proportional to f -0.105. It means that though electrochemical control of pit nucleation dominates, mechanical loading may also play a certain role but it is not primary one.…”

“…Akid et al [25], does not consider the pit-to-crack transition to be a transition state in the above presented sense but a stage which lasts a definite period. In such approach, the pit-to-crack transition time (t p→c ) should be included into the above presented model described by Eq.1 which takes the following form: t f = t pn + t pg + t sc + t lc + t p→c Phenomena, mechanism and partly the modeling of particular pitting corrosion phases has been discussed previously [26].…”

“…For non-alloyed steels, influence of applied cyclic strains on pit nucleation period is not so distinct or is even negligible. Akid et al [25] stated that the first pit appearance which was identified to be a breakdown in a moderately passive layer on steel surface, was controlled rather by electrochemical phenomena acting on metal-electrolyte interface than degree of mechanical damage. In established time periods, the mechanical damage degree was increasing along with increasing number of deformation cycles resulting from increasing load frequency (f).…”

“…Akid et al [25] tested a carbon steel under fatigue loading in a synthetic sea water. They determined a ten-times increased value of pit growth rate as a result of stress range increasing.…”

Controlled Pre-Corrosion Attack and Ultrasonic Fatigue Endurance of Titanium Alloy Ti-6Al-4V

“…In this work, pre-corrosion on the ultrasonic fatigue specimens was imposed and special attention was devoted to the geometry and proximity of pre-corrosion pitting, which were revealed strongly associated with the stress concentration, temperature increase and decrease of fatigue endurance. This behavior has been observed for a large number of metallic alloys (Dolley and Dolley 2000;Akid et al 2006;Zupanc and Grum 2010). Furthermore, most of the stress concentration models for pitting corrosion are related to the geometrical dimensions of one single pit: the depth and width of the pit (Jia et al 2015;Turnbull et al 2010).…”