PSI - Issue 42

Gauri Mahalle et al. / Procedia Structural Integrity 42 (2022) 570–577 Mahalle et al./ Structural Integrity Procedia 00 (2019) 000 – 000

572

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function of punch displacement and the data were acquired by a computer-based data acquisition system. The tests were conducted under displacement-controlled loading with two punch velocities (0.003 and 0.3 mm/min) and temperatures (400-550 ºC). The yield strength and ultimate tensile strength are evaluated using Eqs 1-2 (García et al. 2014). = 0.3 2 (1) = 0.277 . (2)

(b)

Fig. 1. (a) Optical microscopy of commercially available T91 Ferritic-martensitic steel (Tan et al. 2017); (b) Small punch test setup

Table 1. chemical composition of T91 Ferritic-martensitic steel

Elements C

Mn

P

S

Si

Cr

Mo

Ni

V

Fe

% Wt

0.07

0.47 0.02 0.02 0.28

9.24

0.96 0.16 0.21 Bal

3. Results and discussion 3.1. Shear deformation behavior

The experimental load v/s displacement data are shown in Fig. 2(a – b) for mentioned test conditions. It was found that the SPT results were significantly influenced by the strain rate. With a rise in test temperature, the load displacement curve tends to become steeper. The load-displacement curve is typically classified into four zones; Zone I: elastic bending region, Zone II: plastic bending region, Zone III: membrane stretching region and Zone IV: plastic instability region (Arroyo et al. 2017; Contreras et al. 2008). The load-displacement curves in the elastic bending and early plastic bending region almost completely overlap (before the displacement of 0.5 mm). The plastic deformation of T91 steel is dominated by dislocation glide (Shang et al. 2020). With the rise in temperature, dislocation mobility was found to increase and critically resolved shear stress was also found to lower (Dieter 1988).