PSI - Issue 40

N.A. Makhutov et al. / Procedia Structural Integrity 40 (2022) 275–282 N. A. Makhutov, I. V. Makarenko / Structural Integrity Procedia 00 (2022) 000 – 000

279

5

(a) (c) Fig. 3. (a) Scheme of a tubular welded specimen with initial cuts; (b) the isometric image of a crack developing from an initial semi-elliptical notch and finite-element model of the crack of low-cycle fracture: (c) photo of not welded tubular sample with initial semi-elliptical inclined cracks. Cyclic elastic plastic tests were carried out at the coefficient of cycle asymmetry of the cycle -1. On which initial inclined semi-elliptical cracks were applied by the electro-erosion method, through a polished surface samples. At the same time, the depths of the initial incisions (b 0 - small semi-axes of ellipses) varied in the range b 0 = (0.06 - 0.30) t and the large axes varied within 2 a o = (0.003 - 0.045)  D. Here it is the wall thickness of the sample; D is the outer diameter of the sample. The ratio of semi-axles of incisions varied between b 0 /a 0 = (0.18 - 0.80). The angles of inclination of the planes of the original incisions to the axis of the sample (see Fig. 3) were as follows  =  /6;  /4;  /3; 5  /12;  /2. Measurements of crack opening and local elastic plastic strains in the tops of cracks were carried out using an optical system on a precision grid applied to the polished surface of the sample in increments of 0.05 - 0.10 mm. The forming of the surface of the developing cracks according to the depth of the sample was determined by the method of paints. Fig.4 shows the function of critical crack opening from temperature and thickness for weld metal ( , ) f t T CW   (surface contour - ABCDEFG) and fusion zone ( , ) f t T CL   (surface contour - ABCDEFG), well described by empirical equations (4) and (5). (b)

2

(   

) t T   

t  

.

(4)



 

1

2

3

4

CW

2 8 t CL            . 7 6 5 ) t T (

(5)

The coefficients of these equations i  at i= 1, 2, 3... 8 depending on the technological parameters and type of welding, are equal to: м 3 1 0,12 10     , 3 2 5,17 10      , 2 7 3 / 0,25 10 K м      , 2 7 4 5,55 10 1/ K      , м 5 5 5,6 10     , 0,01 6   , 2 7 7 / 0,27 10 K м      , 2 7 8 4,2 10 1/ K       .