PSI - Issue 28

V. Iasnii et al. / Procedia Structural Integrity 28 (2020) 1551–1558 Author name / Structural Integrity Procedia 00 (2019) 000–000

1556

6

The calculated and experimental lifetime dependencies versus the total density energy Σ W t at 0°С under constant loading ( R = 0 and 0.5) are shown on Fig. 7.

a

b

10 12 14 16 18 20

1,E+05

R=const

Power law fit (R=const)

3

1,E+04

3

Σ W t ,MJ/m

W t , MJ/m

2 4 6 8

1,E+03

1,E+02

10

100

1000

10000

N f , cycles

10

100

1000

10000

N f , cycles

Fig. 6. Dependence of the Odqvist’s parameter on the number of loading cycles at R = 0 and R =0.5.

Fig. 7. Dependence of the dissipated energy density on the number of loading cycles at R = 0 and R =0.5.

As it can be seen from Fig. 7, the total strain energy Σ W t can be described by power law function that depends on N f at various stress ratios

p

W N

 



 

t

f

W

(9)

t

The parameters �� � and p (Table 1) in equation (8) were determined by fitting of experimental data. The error between experimental ( N f,e ) and calculated ( N f, p ) lifetime of SMA by the criterion Σ W t does not exceed 25% (Table 2). From the obtained results, that are given in Table 2, the total dissipation energy Σ W d at R = 0 and 0.5 for all tested specimens varies in range (0.017 - 0.155) Σ W t . Only for specimen No. 12 ( N f = 24 cycles) total dissipation energy Σ W dis is equal to 0.25 Σ W t .

Table 2. Experimental ( N f , e ) and calculated ( N f , p ) lifetime of SMA according to Σ W t criterion. Specimen No R σ N f ,e , cycle Σ W d ,MJ/m 3 Σ W e , MJ/m 3 Σ W t , MJ/m 3 Σ W d / Σ W t N f , p ( Σ W t ), cycle

N f , p ( Σ W e ), cycle 2446

10 12 13 14 15 16 17 18 19 20

0 0 0 0 0 0 0

2010

1005

17105 228 6648 5768 7662 10778 5390 36301 7538 20032

18110 306 7282 6730 8455 12749 6098 36925 7700 20550

0,055 0,255 0,087 0,143 0,094 0,155 0,116 0,017 0,021 0,025

2438

24

78

24

24

773 763

634 962 793

872 797

889 764

1201 2053 944 4587 770 3031

1032 1640 713 5449 928 2812

1035 1492 711 5475 1017 2897

1971 708 624 162 518

0.5 0.5 0.5

In general, with the increase of cycles to failure number the relative portion of dissipation energy in the total strain energy density decreases.