13th International Conference on Fracture June 16-21, 2013, Beijing, China rise using a two-dimensional convolution local heat conduction equation under fatigue loadings [7, 8]. Considering the environment temperature and the thermo-elastic effect, the accurate dissipated energy per cycle was achieved [9]. In this paper, a precise temperature measurement experiment program was developed to compute dissipated energy. The variation of dissipated energy per cycle was in-situ monitored during each high-cycle fatigue test process under different stress levels. 2. Theory and Experiment Set-up To achieve the goal of this work, it is necessary to perform precise energy dissipation measurements in high cycle fatigue processing. 2.1. Materials Stainless steel 316L is a low-carbon stainless austenitic steel. It’s composed of 0.03 C, 2 Mn, 0.045 P, 0.03 S, 0.75 Si, 16-18 Cr, 0.01 N, 2-3 Mo, 10-14 Ni (in wt.%). The thermo-mechanical properties of 316L stainless steel are reported in Tab.1. The specimens were machined from a 3mm thick cold rolled sheet and machined in the rolling direction. Before the high cycle fatigue test, three tensile tests was performed to determine the 0.2% yield stress (σ0.2%=295MPa) and ultimate tensile stress (σb =587MPa). Table 1: Thermo-mechanical and Mechanical properties(at 20 oC) ρ C k α E σ0.2% σb Ref. (kg.m−3) (J.kg−1K−1) (m−1.K−1) (10−6.K−1) (GPa) (MPa) (MPa) 316L 7960 500 14 14.8 195 295 585 [10] 2.2. Dissipated energy measurements The dissipative source d1 of the material were computed from the surface temperature fields of the loaded specimen with a rectangular active gauge section (width l=20mm and length lu=30mm). As the surface temperature variations with plastic strain are very small, precise temperature field measurements are required. A step-by-step mathematical description and details about the method performance are available in [9, 11]. A loaded sheet specimen and a dummy specimen were used to dissipated energy measurement. The dummy specimen localized next to the loaded specimen was made from the same material as the loaded one (Fig.1, left picture). It’s used to monitor the environment temperature variation during the temperature filed acquisition. Both loaded and dummy specimens were coated with a thin layer of black paint to enhance their emissivity. To lower the environment noise, an insulation equipment was designed and placed around the specimen. Besides, a black curtain was surrounded to avoid external radiative reflections onto the specimens (Fig.1,right picture). 2
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