Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 30 (2017) 60-68; DOI: 10.3221/IGF-ESIS.37.08 62 amplitude applied to the specimen is measured by a strain gage pasted in each specimen. In order to restrict the cracking location, the fretting damage of one pair of the pads is prevented by inserting a thin polyamide film between the contact surfaces. a) b) c) Figure 1 : Fretting fatigue test [3]: a) Test assembly; b) Specimen geometry (in mm); c) Bridge type contact pad. B. Fatigue tests The tests are carried out in: The University of Chemical Technology and Metallurgy Sofia, Bulgaria; The HYDROGENIUS Institute, Kyushu University, Japan; Sandia National Lab, California & the University of Tufts, Medford, Massachusetts, USA  Fatigue research team at the University of Chemical Technology and Metallurgy, Sofia, Bulgaria [4] investigates and analyses the hydrogen influence on fatigue behaviour of Steel 316L The fatigue tests are carried out under the following conditions: 1. Using a table model Rotating Bending Machine FATROBEM 2004 with a corrosion testing box for environment-assisted short-fatigue-crack-growth investigations and specimens shown in Fig. 2a; 2. Applied loading conditions: cyclic rotating-bending at room temperature and laboratory air; testing frequency of 11 Hz; stress ratio R = −1; stress ranges a  and registered corresponding fatigue lifetimes N f presented in Tab. 2.  Skipper [5] examines the hydrogen influence on Steel 316L by two types of specimens: hydrogen charged and uncharged ones. The hydrogen charging of specimens is performed in the following sequence: 1. Thermal precharging at 573K in 138 MPa hydrogen gas for more than 30 days; specimen’s freezing before, fter tests for minimizing hydrogen loss; 2. Keeping each charged specimen at room temperature for 1 hour before tests; measuring its hydrogen content by inert gas fusion at a commercial vendor. The tests are performed on R. Moore Rotating Beam Fatigue Testing Machine at room temperature, frequency of 50 Hz; constant stress range, a  ; number of cycles to failure, N f , determined by specimen fracture or when sufficient deformation precluded rotation.  Murakami [6-8] investigates the influence of hydrogen on Steel 304, 316, 316L using mainly two types of specimens: hydrogen charged and uncharged ones. The fatigue tests are carried out under the following conditions: 1. Cathodic and gas environment hydrogen charging; 2. Applying of special heat treatment Non-Diffusible Hydrogen Desorption Heat Treatment (NDH-HT) to some specimens for removing non-diffusible hydrogen reaching a level of 0.4 wppm; 3. Drilling of small hole with diameter and depth 100 µm into the specimens; 4. Tension-compression tests at stress ranges 260, 280 MPa, stress ratio R = −1; frequencies 0.0015, 1.5, 5 Hz; a specimen with its hole is shown in Fig. 2b;