is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible.This is an author-deposited version published in: http://sam.ensam.eu Handle ID: .http://hdl.handle.net/10985/8815 To cite this version :Thierry PALIN-LUC, Ruben PÉREZ-MORA, Claude BATHIAS, Gonzalo DOMINGUEZ, Paul C. PARIS, Jose Luis ARANA -Fatigue crack initiation and growth on a steel in the very high cycle regime with sea water corrosion -Engineering Fracture Mechanics -Vol. 77, n°11, p.1953-1962 -2010 Any correspondence concerning this service should be sent to the repository This paper is devoted to the effect of corrosion on the gigacycle fatigue strength of a martensitic-bainitic hot rolled steel used for manufacturing offshore mooring chains for petroleum platforms. Smooth specimens were tested under fully reversed tension between 10 6 and 10 10 cycles in three testing conditions and environments: (i) in air, (ii) in air after precorrosion and (iii) in air under real time artificial sea water flow. The fatigue strength at greater than 10 8 cycles is reduced by a factor more than five compared with non-corroded specimens. Fatigue cracks initiate at corrosion pits due to pre-corrosion, if any, or pits resulting from corrosion in real time during the cyclic loading. It is shown that under sea water flow, the fatigue life in the gigacycle regime is mainly governed by the corrosion process. Furthermore, the calculation of the mode I stress intensity factor at hemispherical surface defects (pits) combined with the Paris-Hertzberg-Mc Clintock crack growth rate model shows that fatigue crack initiation regime represents most of the fatigue life.

is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. Kqwnrds.-High cycle multiaxial fatigue, criterion, energy.

A B S T R A C TThe present work is devoted to the investigation of fatigue crack initiation and growth in middle-cycle fatigue (∼10 5 cycles). Smooth specimens made of 35CrMo4 quenched and tempered steel were loaded in fully reversed plane bending. Temperature field evolution in time was recorded with an infrared camera. The experimental results show that the local heating of metal under fatigue loading is a sensitive and accurate enough manifestation of small fatigue crack initiation. It is shown that the time evolution of the spatial standard deviation of the temperature field can be used to investigate the damage localization and to monitor both the crack initiation and the current location of the fatigue crack tip. This should help to investigate the behaviour of defect during cyclic loading.

International audienceThis paper is focused on the effect of sea water corrosion on the gigacycle fatigue strength of a martensitic–bainitic hot rolled steel R5 used for manufacturing off-shore mooring chains for petroleum platforms in the North Sea. Crack initiation fatigue tests in the regime of 106 to 1010 cycles were carried out on smooth specimens under three different environment conditions: (i) without any corrosion (virgin state) in air, (ii) in air after pre-corrosion, and (iii) in-situ corrosion-fatigue under artificial sea water flow. A drastic effect of sea water corrosion was found: the median fatigue strength beyond 108 cycles is divided by 5 compared to virgin state specimens. The crack initiation sites were corrosion pits caused by pre-corrosion or created during corrosion-fatigue under sea water flow. Furthermore some sub-surface and internal crack initiations were observed on specimens without any corrosion (virgin state). Crack propagation curves were obtained in mode I in air and under sea water flow. Calculation of the stress intensity factor at the tip of cracks emanating from hemispherical surface pits combined with the Paris–Hertzberg–Mc Clintock crack growth rate model showed that fatigue crack initiation period represents most of the fatigue life in the VHCF regime. Additional original experiments have shown physical evidences that the fatigue strength in the gigacycle regime under sea water flow is mainly governed by the corrosion process with a strong coupling between cyclic loading and corrosion