PSI - Issue 13

N.V. Boychenko / Procedia Structural Integrity 13 (2018) 908–913 Boychenko N.V. / Structural Integrity Procedia 00 (2018) 000–000

910

3

The test materials used in this study are an aluminum alloys D16T and V95, their main mechanical properties for room, high (250°C) and low (-60°C) temperatures are listed in Table 2, where E is the Young’s modulus,  b is the nominal ultimate tensile strength,  0.2 is the monotonic tensile yield strength, n is the strain hardening exponent, and α is the strain hardening coefficient.

Table 2. Main mechanical properties of aluminum alloys D16T and V95

Temperature, °С

α

n

E GPa

 0.2 MPa 407.6

 b MPa

Aluminium alloy

-60

545 590 339 621 652 273

80.95

5.325

2.63 1.50 1.44

Д16T

20

438 294

73.261 75.246 75.239 83.704 48.122

5.88 8.39 7.69 14.3 14.9

250 -60

507.6

1.634

В95

20

560

1.30 0.35

250

163.2

The load value was selected to provide the same level of nominal stresses in the middle section of the specimen under the considered loading type, namely P = 10kN for three-point bending and P = 50kN for uniaxial tension. ANSYS finite element (FE) code (2012) is used in mechanical analysis. 3. Elastic and plastic stress intensity factors The elastic stress intensity factor under uniaxial tension and three-point bending conditions is defined as Murakami (1987): 6 tw M   . where  - nominal stress, F 1 – geometry dependent correction factor, a and с – crack length and depth correspondently, w – specimen width, t – specimen thickness. The plastic stress intensity factor Kp for small-scale yielding in pure Mode I can be expressed directly in terms of the corresponding elastic stress intensity factor as follows (Shlyannikov (2014 a)): where K K w / 1 1  is elastic SIF normalized by a characteristic size of cracked body,  and n are the hardening parameters, λ= a/w is the dimensionless crack length, and σ 0.2 is the yield stress, I n is governing parameter for 3D fields of the stresses and strains at the crack tip. FE-analysis of the near crack-tip stress-strain fields. In this study, the numerical integral of the crack tip field I n changes not only with the strain hardening exponent n but also with the relative crack length c/w and the relative crack depth a/t .                                                          d u u d du u d du u n n n c w a t I FEM FEM r FEM r FEM rr FEM FEM r FEM r FEM r FEM FEM rr n FEM e FEM n cos . ~ ~ ~ ~ 1 sin ~ ~ ~ ~ cos ~ ~ ~ 1 ( , ,( / ),( / )) 1 (3)           ; ; ; 1 c aF a 1 w c t a K (1) under uniaxial tension tw P   , under three point bending 2     1/ 1  n   I Y a w    1/ 1  n 2 1 2    0 0 2 1 ( / )                      I K K FEM n n p       (2)  

      

      

1

n



More details in determining the I n factor for different test specimen configurations are given by Shlyannikov et al (2014 a).