2.2 Non-Standard MTP Specimen Design, Test Rig and Experimental Set-Up
Fig.2a shows the geometry and dimension of the non-standard MTP specimens designed for high temperature LCF and CF tests. Thus, three values of l 0/d0 were chosen, i.e., l 0/d0 = 1.0 (MTP-1), l 0/d0 = 1.5 (MTP-2), and l 0/d0 = 2.0 (MTP-3), with the constant values, such as thickness (t = 0.5 mm), gauge width (d0 = 1.0 mm), total width (w = 2.0 mm), and fillet radius (r = 2.0 mm). It should be mentioned that for the MTP specimens, size effect50-52in the thickness direction should be considered. Based on the previous findings in the refs51-52, the number of grains in the thickness direction should exceed at least 5 ~ 6 grains in order to minimize the size effect, which is the basic principle for designing the thickness of MTP specimen in this study. According to the measured prior austenite grain size reported in the previous work1, there are approximate 10 grains in the thickness direction. The MTP specimens with differentl 0/d0 values are shown in Fig.2b. The loading assembly and experimental set-up is shown in Fig.2c, where the loading assembly is made of Nimonic 80. The polished MTP specimen is clamped at both ends by specially designed and manufactured clamps with machined rough surfaces to minimize the misalignment, strengthen the grip and reduce the slippage, see Fig.2d. The displacement is measured by two linear variable displacement transducers (LVDT) connected to both sides of the loading part of the machine.