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.