Presented at the 23th International This research was possible thanks to the financial support of BOF 2 University of Maribor, Laboratory for Machine Parts and Structures, Slovenia 3 Ghent University, Dept. Materials Science and Engineering, Belgium Basic fatigue properties Corrosive environment decreases fatigue life Two types of specimens are evaluated: 1) Round bar for S-N curve analysis: Seawater is corrosive and accelerates the fatigue proccess. An environmental chamber was built to test fatigue in a realistic corrosive situation. Corrosion is a slow process and must be accelerated to allow an increased fatigue testing frequency. The authors would like to acknowledge the financial support of the IWT (Agency for innovation by science and technology – grant n°131797). Nahuel Micone*, Wim De Waele. Ghent University, Dept. Energy and systems, Soete Laboratory, Belgium Fatigue Analysis of Steels used in Offshore Structures Subjected to Variable Amplitude Load Conditions Two high strength low alloy steels (yield stress of 520 and 610 MPa) are tested in “realistic” conditions (variable amplitude loads and corrosive environment). 2) ESE(t) for Fracture Mechanics analysis: Corrosion chamber Tensile testing machine Number of cycles up to failure Crack growth rate (CGR) Variable amplitude (VA) analysis is more accurate Offshore industry is growing fast. Since new generation steels and design techniques are not updated in the standards, designs can be over conservative. Wave spectrum Structural response Wave height (m) -5 5 Time Force (kN) -3000 3000 Time Force (kN) -3000 3000 Easier to test and interpret Difficult to test and interpret Analysis Time Random Crack growth (mm) Cycles Slow Fast a 0 Cycles Stress (MPa) Infinite life Finite life Fatigue failure Possible corrosion-fatigue interaction Infrared & Potential Drop Presented at FEA symposium 2015 09 December 2015, Gent, Belgium Accelerated corrosion test setup Physical kinetics analysis * Cycles Temp (°C) Failure (N f ) Voltage (V) T 1 V 1 V 0 T 0 Area=damage N fi =f(Area i ) Cycles Stress (MPa) N f1 N f2 N fi S i S 2 S 1 Digital Image Correlation & Electrical Measurements Crack growth (mm) Cycles a 0 S-N Fracture mechanics *[email protected] Realistic test conditions give accurate predictions. VA loading can accelerate/retard the CGR. Corrosion might be the driven damage mechanism at low stress levels Cycles (x10 6 ) Stress (MPa) Corrosion influence Stress influence 0 2 4 6 CA+Air VA+Seawater Curve for CA Curve for VA ? Crack growth (mm) Cycles (x10 5 ) Underloads=acceleration Overloads=Retardation Unconservative Over conservative a 0 0 1 2 3 Low-High blocks Time Force (kN) -3000 3000 Electrical resistance F min F max F min F max Heater Temp Oxigen Seawater Easier to test and interpret High-Low blocks Temperature (°C) Corrosion rate (mm/y) Log da/dN Log DK Corrosion influence Stress influence Stress intensity factor: CA+Air VA+Seawater