Development of a miniature-disk bending fatigue specimen

A miniature-disk bending fatigue specimen was earlier developed for testing materials to be used for fusion reactor applications. The specimen is based on a 3-mm-diameter transmission electron microscope disk. A second larger rectangular specimen was also developed, with dimensions of 30.16 by 4.76 by 0.76 mm. The specimens, made from annealed type 316 stainless steel, were testing using a specialized bending fatigue machine at temperatures of 25, 550, and 650 C. In the current study, the results are compared against standard full-size specimen results. Strain ranges were calculated using an analytical technique based on specimen geometry and material properties. For the rectangular specimen, strains were also measured using strain gauges attached to the gauge region. The calculated strains were then modified using a calibration factor based on the measurement. The rectangular specimen results were in good agreement with ASTM full-size specimen results. The miniature-disk specimen data fell below the other results, indicating that the analytical technique underestimates strain values. No clear temperature dependence was evident for the miniature-disk specimen, unlike larger specimens which show a degradation of fatigue properties with increasing temperature. The miniature-disk specimen results also show a greater scatter about the best-fit curve, which was attributed to greater sensitivity to misalignment