PSI - Issue 5

Yoichi Kayamori et al. / Procedia Structural Integrity 5 (2017) 279–285 Yoichi Kayamori et al. / Structural Integrity Procedia 00 (2017) 000 – 000

281

3

c 

 3.5 

(1)

c is calculated by the following equation, where a is the crack depth and F is the shape parameter for the stress intensity factor, K , in a finite plate: 2 c a F  (2) Nagai et al. (1980) carried out the structural model tests and analysis of welded joints made of mild steel plates for shipbuilding, NK KAS, and produced the following design curve that is composed of two equations for elastic and plastic strain regions, where  y is the yield strain. Nagai et al. also demonstrated that the design curve was approximately applicable to high strength steel plates such as JIS HT80 and SM41B (1982, 1984).

         

2

   

   





for

(3 ) a

2

1







y

y





c



y

   

    





for

(3 ) b

3.5

1.5

1







y

y

The current JWES CTOD design curve (2011) is different from Eqs.(3a) and (3b), and is given by the following equations. The gradient of Eq.(4b), 9  / 8 , is almost equivalent to 3.5, which is the gradient of Eqs.(1) and (3b).

         

2

   

   







  

  

for

(4 ) a

1



2





y

y





c



y

   

   

   

    







  

  

for

(4 ) b

9

5

1



8





y

y

These equations from (1) to (4b) do not contain Y/T , and these CTOD design curves do not relate to Y/T .

2.2. Formulation of a new CTOD design curve

Considering a dimensionless constraint factor, m , which is a function of Y/T , a new CTOD design curve is formulated by using m in this study. According to Linear Elastic Fracture Mechanics (LEFM), relationship between  and J is given by in the following equation, where  y is the yield stress, G is the energy release rate, E is Young ’ s modulus and  is the stress corresponding to the boundary force:   E c E J G K m y 2 2         (5)

This results in an equation of  in the following form: