PSI - Issue 6

Alexander K. Belyaev / Procedia Structural Integrity 6 (2017) 201–207 A.K.Belyaev et al. / Structural Integrity Procedia 00 (2017) 000–000

204

4

(a)

(b)

150

R 30

100

30

σ ,MPa

40

50

145 300

60

0

0

5

10

15

20

25

30

ε

axial

Fig. 1. (a) Geometry of the test specimen; (b) Dependence of axial stresses σ on the axial strains ε axial of the specimen during stepwise loading.

(b)

(a)

6.36

3.30

V

( ε )

1

3.28

6.35

V

( ε )

2

3.26

6.34

3.24

6.33

3.22

6.32 V 3 ,mm/mcsec

3.20 V ,mm/mcsec

6.31

3.18

6.30

3.16

0

0.05

0.10

0.15

0.20

0.25

0.30

0

0.05

0.10

0.15

0.20

0.25

0.30

ε

ε

local

local

Fig. 2. (a) Dependence of the velocities of transverse waves v 1 and v 2 on local deformations ε local ; (b) Dependence of the velocity of longitudinal wave v 3 on local deformations ε local .

in the spatial inhomogeneity of plastic deformations and it is reflected in the form of stress relief in the case of rigid loading in the process of elasto-plastic deformation. To minimize the Portevin-Le Chatelier influence, measurements of local deformations of the specimens were carried out in the area of measurement of acoustic anisotropy by using a high-precision strain gage with a measurement base of 10 mm and an accuracy of 10 − 4 mm. The dependence of axial stresses on axial deformations reflects the influence of the Portevin-Le Chatelier e ff ect (cf. Fig. 1b). Measurements of the specimen thickness at each stage of loading allow to obtain the dependences of the transverse waves of mutually orthogonal polarization (cf. Fig. 2a) and the dependence of the longitudinal wave on the local deformations measured at the center of the specimen (cf. Fig. 2b). The dependencies of the principal values D 1 and D 2 of the damage tensor on local deformations ε local are shown in Fig. 3a. The principal values D 1 and D 2 are responsible for the accumulation of damage along and orthogonal to the axis of the specimen, which coincides with direction of the action of the load. A comparison of the results of acoustic anisotropy according to various schemes of symmetrization and its experi mental values was carried out to establish the relationship between acoustic anisotropy and damage (cf. Fig. 3b). The dependence of acoustic anisotropy on the stresses is shown in Fig. 4a and the dependence on the local defor mations is shown in Fig. 4b.

4. Discussion

The linear decrease in the velocities of the longitudinal and two transverse waves in the region of elastic deforma tions (less than 0.2%) is changed by a nonlinear decrease in the region of elasto-plastic deformations (cf. Fig. 2a,b). It can be an important indicator for the nondestructive testing of engineering structures.