Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 30 (2017) 60-68; DOI: 10.3221/IGF-ESIS.37.08 60 Focussed on Multiaxial Fatigue and Fracture Analysis of fatigue behaviour of stainless steels under hydrogen influence D. Angelova University of Chemical Technology and Metallurgy donkaangelova@abv.bg, http://orcid.org/0000-0001-2345-6789 R. Yordanova, S. Yankova University of Chemical Technology and Metallurgy r.yordanova@uctm.edu, http://orcid.org/0000-0002-2345-6790 svetla_y@abv.bg, http://orcid.org/0000-0002-2345-6791 A BSTRACT . Three stainless steels – ASTM 304, 316 and 316L - used in hydrogen utilization equipment are under investigation at conditions of tension-compression, rotating-bending and fretting fatigue. Fatigue tests are carried out with hydrogen charged and uncharged specimens. Hydrogen charging includes cathodic type of charging and exposure to high pressure hydrogen gas. The experiments under rotating bending and tension- compression fatigue are conducted under different frequencies in three different laboratories: at The University of Chemical Technology and Metallurgy, Sofia, Bulgaria; at Sandia National Laboratory, California and The University of Tufts, Medford, Massachusetts, USA; The HYDROGENIUS Institute at Kyushu University, Japan. The fretting fatigue tests are presented by The HYDROGENIUS Institute at Kyushu University, Japan. The obtained results are presented in Wöhler curves complemented by plots "Short fatigue crack length– Number of cycles" and “Tangential force coefficient–Stress amplitude”. The found fatigue characteristics are analyzed and compared at different loading conditions, showing the best performance of Steel 316L. K EYWORDS . Tension-compression fatigue; Rotating-bending fatigue; Fretting fatigue; Stainless steels; Short fatigue crack; Hydrogen influence. I NTRODUCTION here are many investigations done into one of the most attractive alternative energy technologies, the hydrogen technology, including hydrogen produce, and hydrogen storage and infrastructure. Although over the last years hydrogen vehicles and utilization machines are in active use across the world, there are still questions to be answered about hydrogen influence on fatigue and fretting fatigue of alloys used in hydrogen fuel cells, engines, compressors, storage tanks, pipes and different members of hydrogen transportation elements. The most frequently used alloys are austenitic stainless steels. It is known that hydrogen environment can affect steel microstructure having changed steel crystal lattice mechanical properties and fatigue life. T