13th International Conference on Fracture June 16-21, 2013, Beijing, China 3. Results and discussion It’s known that in high fatigue test, damage is created slowly by dislocation pile-ups due to the small and gradual changes in the material microstructure. A test sequence was proposed to observe dissipated energy variation during the high cycle fatigue process, to better underline the in-situ thermo-mechanical modifications of materials. Serval specimens were loaded fromσmax=280MPa to 440MPa in steps of 20MPa withRσ=0.2 andf=14Hz. Different constant amplitude fatigue tests (13 levels,30 specimens) were run until the specimen complete separation under traction-traction loadings (Tab.2). In each fatigue test, serval dissipated energy measurements were performed every 5,000, 10,000 or 30,000 cycles for different stress levels fatigue tests. Table 2: Fatigue test results of 316L stainless steel (Rσ=0.2,f=14Hz) Specimen σmax σm σa Nf Em d1 at 30,000 cycles Results number (MPa) (MPa) (MPa) to failure (J·m−3·cycle−1) 1 440 264 176 64,300 40,633 Failure 2 420 252 168 72,897 36,842 Failure 3 420 252 168 76,087 38,425 Failure 4 400 240 160 91,580 34,568 Failure 5 400 240 160 105,348 34,183 Failure 6 390 236 156 127,456 – Failure 7 380 228 152 145,770 – Failure 8 380 228 152 146,425 28,712 Failure 9 380 228 152 149,296 25,245 Failure 10 375 225 150 172,776 20,792 Failure 11 375 225 150 184,285 19,982 Failure 12 370 222 148 178,784 19,875 Failure 13 350 210 140 164,713 19,178 Failure 14 350 210 140 245,817 18,303 Failure 15 320 192 128 291,264 9,532 Failure 16 320 192 128 277,642 10,475 Failure 17 310 186 124 305,381 8,502 Failure 18 310 186 124 663,809 6,006 Failure 19 310 186 124 719,016 6,882 Failure 20 310 186 124 345,773 – Failure 21 310 186 124 581,912 6,917 Failure 22 310 186 124 503,891 7,582 Failure 23 310 186 124 513,625 7,690 Failure 24 310 186 124 465,469 6,560 Failure 25 310 186 124 551,751 6,940 Failure 26 310 186 124 482,605 7,429 Failure 27 300 180 120 696,100 6,559 Failure 28 300 180 120 1,200,000 4,773 No Failure 29 290 174 116 2,000,000 4,317 No Failure 30 280 168 112 2,000,000 3,499 No Failure Fig.5 and Fig.6 are dissipated energy variations in term of fatigue cycles ratio at different stress levels from 6
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