PSI - Issue 28

NikolayA. Makhutov et al. / Procedia Structural Integrity 28 (2020) 1347–1359 N.Makhutov, D.Reznikov / Structural Integrity Procedia 00 (2020) 000–000

1357

11

σ 2c

b

μ σ 1c

σ 3c

0

x

δ

b

b- δ

σ 1c σ 2c

δ

δ

(а)

b

(б)

Fig.5. The stress state in the notch zone (a) the direction of principal axes (b) change in σ 2 over the thickness of the specimen Then using expression (25) one can estimate the value of the strain hardening exponent in the notch zone m c =0.129. Nominal stresses and strains for three-point bending problem (according to Fig.2) are determined using the relationships of the strength of materials:

3 bh l

3

W M

bh PL

2 W bh x  ;

0 x M PL  ;

;

,

(33)

P 

x n   

0

2

2

2

2

6

4

x

where M x is the maximum bending moment in a dangerous cross section, L 0 is the distance between the supports, W x is the axial moment of resistance. At the first stage of impact loading of the specimen (Fig. 4) elastic deformation will continue until σ n K t ≤σ y and elastic strain at e n ≤σ y / E . Using expressions (8), (9), (4), (5), (25), and (26) the values of the key design characteristics were estimated for the cases of: - static tension at room temperature + 20 0 С (293 K ), (curve 1 in Fig. 1; Regime 1 in Table 1); - static tension at the lower temperature of -80 0 С (193 K ), (curve 2 in Fig. 1; Regime 2 in Table 1); - dynamic tension at the room temperature (Regime 3 in Table. 1); - dynamic tension at the lower temperature (curve 3 in Fig. 1; Regime 4 in Table 1). In the calculations, the following values of parameters were taken: σ y0 =252 МPа; S f =1070 МPа; ψ f0 =54,3%;  Т =130; t е   =0,08; е 0 =1,1ꞏ10 -3 s -1 ; е  = 1,25ꞏ10 2 s -1 . On the basis of equation (9) at the relative fracture energy can be estimated (Makhutov, 1981; Makhutov, 2008).

1

f e



.

(34)

1

m



de

e



  



f

f

1

m



0

The results of calculations are given in Table 1.