PSI - Issue 14

3

Taslim D. Shikalgar et al. / Procedia Structural Integrity 14 (2019) 529–536 T.D.Shikalgar et al./ Structural Integrity Procedia 00 (2018) 000–000

531

ߪ ൌ ߝܭ ௣௡

(1)

where, ‘ K ’ is a coefficient and ‘ n ’ is hardening exponent.

Table 2. Mechanical properties at room temperature Material E (MPa)

σ YS (MPa)

σ UT (MPa)

K (MPa)

n

20MnMoNi55

203000 203000

420 544

586 684

927.10 921.55

0.1521 0.0848

T91 (SCK.CEN-R-4122 (2005))

Fig.2. Schematic diagram of the experimental test setup of the SPT test

Fig.1.Experimental true stress v/s plastic strain curves

Fig. 3. Experimental load v/s punch displacement data for pre-cracked specimens of material (a) 20MnMoNi55, and (b) T91.

2.2. Pre-cracked small punch test A pre-cracked small punch test setup is developed as per the recommendations given in CEN code (2007). Some of the important dimensions of the test setup are shown in Fig.2. The geometry of p-SPT specimen used in present work is 10 x 10 mm with a thickness of 0.5 mm. The square specimen having initial thickness t 0 mounted in the lower die is loaded centrally by a punch with a hemispherical ball. The small punch tests are conducted at room temperature with a dynamic mechanical analyzer (DMA) machine in Reactor Safety Division (RSD), Bhabha Atomic Research Centre (BARC), Mumbai. The p-SPT specimens having crack length of 4 mm are manufactured using wire EDM technique. The minimum radius achieved at the crack tip is 0.1 mm. Polishing of both the surfaces of specimens is carried out using P600 to P2400 grit size abrasive paper. The final thicknesses of the specimen are measured at five locations and average thickness value (t 0 ) of each specimen is used in the numerical analysis described later. The experimental load v/s punch displacement data of pre-cracked specimens of both the materials are shown in Fig. 3. Standard regions in load v/s punch displacement data of small punch test as reported by E. Martinez-Paneda