PSI - Issue 68

Nedeljko Vukojević et al. / Procedia Structural Integrity 68 (2025) 379– 385 N. Vukojević et al. / Structural Integrity Procedia 00 (2025) 000–000

382

4

Table 3. Parameters and their levels relevant for the design of the experiment Symbol Meaning Level 1

Level 0

Level 2

Degree of freedom

R eH (x 1 )

Yield strenght (MPa)

R eH1

R eH0

R eH2

1

D (x 2 )

Diameter (mm)

D 1

D 0

D 2

1

t (x 3 )

Thickness (mm)

t 1

t 0

t 2

1

HT (x 4 )

Heat treatment

Before PWHT

-

After PWHT

1

3. Experimental procedure Tab. 4 shows the results of conducting the experimental procedure on the basis of the defined experimental plan. The impact tests were done at room temperature +20°C. The test procedure was performed according to BAS EN ISO 148:2016 on standard test specimens BAS EN ISO 9016:2012. The test was performed on a Charpy pendulum 300 J. Experimentally determined fracture mechanics parameter J-integral was analysed according to the procedure described in ASTM E399 and ASTM E1820.

Table 4. Global plan matrix of experimental procedure

Factors

Output function Y i-j

KV [J] 103

Tretment

Exp. point

R eH [MPa]

D [mm] 1500 1500 3000 3000 2250 2250 1500 1500 3000 3000 2250 2250

T [mm]

K JIc [MPa·m 1/2 ]

X 1

X 2

X 3

9 5

-1

S235 P460 S235 P460 S355 S355 S235 P460 S235 P460 S355 S355

-1 -1

1

14

45,4 60,1 51,8 52,2 41,1 41,1 34,1 32,9 33,7 30,6 42,9 42,9

1

-1 -1

6 6

15 36 42

10

-1

1 1 0 0

6 1 2

1 0 0

1 0 0

14 10 10

PWHT

132 139

BLOCK 1 – Before

11

-1

-1 -1

-1

6

64 57

7

1

1 1

14 14

12

-1

1 1 0 0

184

8

1 0 0

-1

6

40

BLOCK 2 – After PWHT 3

0 0

10 10

131 134

4

For the basic three factors as input parameters R eH , D and t , where the natural logarithm function was applied as a transformation function with regard to the assumed complex polynomial mathematical model of the function, the requested KV and K JIc output sizes were obtained depending on the input parameters:

!

! " # $%CD() *H , - K / ! ! ! = " + +

" $%C D()*HI J K / M 1 ! ! ! = " + + #

and

.

... (2)

In order to translate the complex mathematical model of the observed process into a quasi-linear model suitable for carrying out the planned experiment, as well as regression and dispersion analysis, the principle of logarithmization is applied, and the following form is obtained: and . ... (3) *H,- *HK / M 1 ! ! ! = + + + O 3 ! ! ! = + + +

*HI JK/ JKM 1

! "#$%CD

(

)

! "#$%CD

(

)

By replacing the members shown above in the form: