PSI - Issue 61

Zhichao Wei et al. / Procedia Structural Integrity 61 (2024) 26–33 Z. Wei et al. / Structural Integrity Procedia 00 (2024) 000–000

31

6

(a) mon-T6

(b) cyc-T6

8 10

8 10

4

4

Exp-axis 1 Sim-axis 1 Exp-axis 2 Sim-axis 2

Exp-axis 1 Sim-axis 1 Exp-axis 2 Sim-axis 2

F [kN]

F [kN]

0

0

-4

-4

-0.5

0

0.5

1

-0.5

0

0.5

1

u ref [mm]

u ref [mm]

(c) mon-T9

(d) cyc-T9

8 10

8 10

4

4

Exp-axis 1 Sim-axis 1 Exp-axis 2 Sim-axis 2

Exp-axis 1 Sim-axis 1 Exp-axis 2 Sim-axis 2

F [kN]

F [kN]

0

0

-4

-4

-0.5

0

0.5

1

-0.5

0

0.5

1

u ref [mm]

u ref [mm]

Fig. 3: Force-displacement curves for monotonic and cyclic tests.

(c) mon-T9 FP

(b) cyc-T6 FP

(a) mon-T6 FP

(d) cyc-T9 FP

EXP SIM

EXP SIM

EXP SIM

EXP SIM

A 1

A 1

A 1

A 1

0.23

0.23

0.18

0.34

0.00

0.00

0.00

0.00

Fig. 4: Experimental and numerical distributions of the first principal strains A 1 on the notched surfaces (FP = fracture point).

The numerical prediction indicates inhomogeneous stress triaxialities η distributed across the notched cross sections because stress tends to localize in the center of the notched cross-section. Thus, the mean stress triaxiality ¯ η is utilized to characterize the stress state for the numerical analysis and is defined as

1 S

S

I 1 3 √ 3 J 2

¯ η =

η ds with η =

(9)

,

0

where S denotes the total area of the notched cross-section, and I 1 = tr( T ) and J 2 = 1 2 dev T · dev T are the first and second deviatoric stress invariants, respectively. The mean stress triaxialities for mon-T6, cyc-T6, mon-T9, and cyc T9 experiments at FPs are 0.39, 0.43, 0.58, and 0.59, respectively. Di ff erent stress states are successfully generated by superimposing di ff erent preloads, with higher stress triaxialities induced by larger preloads. However, monotonic and cyclic loading patterns show only a slight di ff erence. On the other hand, stress triaxialities slightly alter during the cyclic loading processes. For instance, the stress triaxialities for cyc-T9 at reverse point (RP1), reverse point (RP2), and FP are 0.59, 0.54, and 0.59, respectively. The stress triaxialities at RP1, RP2, and FP are 0.36, 0.37, and 0.43 for the cyc-T6 experiment.