PSI - Issue 14

Ilyin A.V. et al. / Procedia Structural Integrity 14 (2019) 964–977 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

976

13

m

   

   



7 10

Rb

N

.

(17)



i

K

 

ef

For example, for loading in seawater without protection,     for MPa 148 for MPa 94 18 Rb      r

r

3,



i

(18a)

r

3,



i

Rb

Rb 3.21 lg 4  

 m

.

(18b)

K ef is obtained as a product K ef = K s  K eq , where K eq is a function of K w and r . The calculated data are well described by the formula Q eq K K w  , (19) here Q varies from 1 at high cyclic asymmetry to 0 at fully compressive loading cycle that physically corresponds to the transition of propagating fracture from WTZ into base metal. The calculation has allowed finding an approximating function   i i i r r arctg Q r    1 (1 ) . (20) The procedure of N c assessment is grounded on the integration of the formula (10) with substituted experimentally found parameters, formula (11). In this case the cyclic asymmetry factor r c in general different from r is calculated from the formulae

IR    Ires Ires IR K K K K K

r



for tensile design stress,

(21a)

c

Id

IR K K r K K K c     Ires

Id

for compressive design stress.

(21b)

Ires

IR

Figure 8 – Dependences N c vs.  for welded joints of 20 to 70 mm thickness with a symmetric X or K-type groove, fracture nucleates from a WTZ concentrator. 1. S  60 mm, σ R = 0, r = -  . 2. S  60 mm, σ R = 200 MPa, r = -  . 3. S  60 mm, σ R = 350 MPa, r = -  or σ R = 0, r = 0. 4. 20  S  70 mm, σ R = 350 MPa, r = 0.