PSI - Issue 14

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

968

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gusset for section A─A is greater then

Figure 1 – Welded joint with structural stress concentration. Technological stress concentration factor K w

K w T-joint for section B ─B. The generalization of FEM calculation results gives a representation of K w suggested by Ilyin et al (1983):    / 1 w K A . (4) For joints in the “as - welded” state the parameter  shows a high-scatter random nature. It has been shown by measurements with impressions that a local  value can vary by an order and more (from 0.1 mm up to 3.0 mm) within the weld length of 5 mm. The parameters of  distribution (mean value and standard deviation) may be considered as constants for a specific welding procedure. A set of interpolation formulae have been offered by Ilyin et al (1983) and Gorynin et al (1990) to find K w for typical welded joints. For example, parameter A for T-joints can be found as 0.5 3 2 1 0.5 2 sin        T h a T b a S a A . (5) When the nominal stress range  σ is greater than S c  K t , a zone of plastic deformation with a factor of cyclic asymmetry r =  1 appears. If a cyclic stress-strain diagram is approximated by a power law      ( / ) c c S , the factor K  can be found as suggested by Ilyin et al (1983):   (1 ) /(1 ) ) 2/(1 t 1/( 1) / 2 1              c S K K . (6)         

Investigations of the authors have shown that for steel with  Y > 400 MPa acceptable values are   MPa 400 0.3 0.4 10 1.3 , Y 3 Y          c S .

If the weld metal has a yield stress much lesser than base metal, plastic strain occurs in weld metal only, Figure 2. The function K I ( a ) is very important to simulate the process of fracture in WTZ. It was derived from FEM results: K Y a     1 , (7)

a     4.5

a . It is necessary to note that formula (7) predicts nonzero K I value if a  0 and  0. A Y   1 0.44 1