PSI - Issue 24

Riccardo Panciroli et al. / Procedia Structural Integrity 24 (2019) 593–600

595

R. Panciroli and F. Nerilli / Structural Integrity Procedia 00 (2019) 000–000

3

300

1000 1200 1400 1600

250

200

0 200 400 600 800

150

100

True Stress [MPa]

True Stress [MPa]

50

0

0

2

4

8

0

10

20

30

40

6

50

True Strain [%]

True Strain [%]

Fig. 1. Typical stress-strain curve for a nitinol wire at a strain rate of 10 − 3 . Full test on the left and detail of the shape memory range on the right.

response is then elastic until approximately 1000MPa, to later yield and accumulate irrecoverable plastic deformation. The final failure of the wire is always attained above 40% elongation.

Table 1. Nitinol material properties implemented in the numerical model. E 0 ν C 1 T 0 C 3

C 4

C 5

E m

22Pa

0.36

222

290 K

130 MPa

8.0

0.066

15GPa

The material response has been implemented numerically utilizing the SMA material model available within the ANSYS software by activating the MEFF option, which identifies the shape memory e ff ect. Such option overrides the default superelastic behavior. The first six constants required by the model have been evaluated from the experimental results and are reported in Table 1. The numerical model allows for a seventh parameter, which identifies the Lode dependency function of the material. Such value has been set to zero. The results from a simulated elongation test are reported in Figure 2 alongside with a schematics of the simplified SMA model with overlaid characteristic points and constants.

300

C 3 = S A s 2 C 4 = β ( T − T 0 ) 3 2 C 5 = ε l 3 2 C 1 = 3 2 h 2 3 σ AS f − σ

σ

250

E m

200

E 0

σ AS f

150

C 1

σ AS s

C 3

100

σ S A s

C 4

True Stress [MPa]

σ S A f

50

ε l

0

ε

0

2

4

8

6

True Strain [%]

Fig. 2. Simplified SMA stress strain curve cycle with highlighted characteristic points (left) and numerical results of the implemented material undergoing a monotonic elongation test (right).