PSI - Issue 3

A. Strafella et al. / Procedia Structural Integrity 3 (2017) 484–497 A. Strafella, A. Coglitore, E. S l rnitano / Structural Integrity Procedia 0 (2017) 000–000

489

6

Creep Strain % - [560MPa] Fit Lin - [558MPa]

Derivative Creep Strain - [560 MPa]

0,00 0,25 0,50 0,75 1,00 1,25 1,50 1,75 2,00 2,25 2,50 2,75

0,025

0,020

0,015

0,010

0,005

Creep Strain [%]

0,000

sscr-Derivative creep strain [%/h]

-0,005

0

200

400

600

800

1000

1200

Time [h]

Fig. 5. Typical sscr calculus: minimum of first derivative and fit linear of secondary creep stage.

The steady strain creep rates were plotted in a log–log graph. Figure 6 shows the variation of sscr with the applied stress.

Fig. 6. log–log plot of sscr-stress points.

The variation of sscr with applied stress obeys a power law relationship in the form of Norton-type:

n sscr A σ =

(1)

where σ is the applied stress, n is the stress exponent, and A is an empirical constant. For 15-15Ti(Si) steel, the found A and n values are showed in Table 3.