PSI - Issue 14

Bimal Das et al. / Procedia Structural Integrity 14 (2019) 619–626 Das et al./ Structural Integrity Procedia 00 (2018) 000 – 000

621

3

Nomenclature σ

stress tensor

p 

plastic strain tensor

s

deviatoric part of stress tensor size of current yield surface deviatoric total backstress tensor

0 σ

   i 

components of total deviatoric backstress tensor

increment in plastic strain tensor

d p 

( ) ( ) i f a

magnitude of decomposed back stress tensor

  i  , ( ) i r kinematic hardening coefficients

  i C ,

2. Experiments

The as received P91 steel used for the present investigation has been received in the form of plate having thickness 6.7 mm. The chemical composition of P91 steel is listed in Table 1.The material has been normalized for 90 min at 1050 °C followed by tempering for 60 min at 760 °C.

Table 1. Chemical composition of P91 steel. Element C Cr Mo Mn Si

V

Ni

Nb

N

Al

P

S

Fe

Wt. %

0.12

8.67

0.91

0.37

0.24

0.19

0.11

0.075

0.05

0.02

0.002

0.002 Balance

The monotonic tensile tests are conducted using closed-loop servo-hydraulic controlled universal testing machine (INSTRON 8802) at room temperature in ambient air under constant strain rate of 10 -3 s -1 . The strain was monitored using an extensometer of gauge length 25 mm. The evaluated mechanical properties are tabulated in Table 2.

Table 2. Mechanical properties of P91 steel. Yield strength (MPa)

Ultimate tensile strength (MPa)

Uniform elongation (%)

Total elongation (%)

546

711

10.57

22.9

Fig. 1. Geometry of the low cycle fatigue specimen according to ASTM E606.

All Symmetric and asymmetric (R ≠ -1) strain controlled tests are performed at room temperature on a closed loop servo-hydraulic machine equipped with a load cell of 100 KN. Triangular waveform loading with different strain ratios were imposed at a constant strain rate of 10 -3 s -1 . The geometry of the fatigue test specimen designed according to ASTM E606 standard is depicted in Fig. 1. During the tests, the strain was monitored by engaging an extensometer of gauge length 12.5 mm to the gauge position in the specimen. The test parameters under different loading conditions are presented in Table 3.