Issue 35

A. Tzamtzis et alii, Frattura ed Integrità Strutturale, 35 (2016) 396-404; DOI: 10.3221/IGF-ESIS.35.45

Material with HAZ cyclic local properties

actual crack length

r c

Figure 1 : Incremental crack growth in HAZ.

at the position of fracture r c

for an isotropic linear

By calculating in Eq. (5) for mode I loading the stress amplitude σ A elastic material and by and using the Coffin-Manson relationship [21-22] to derive Δε p,,

the crack growth equation can be

derived:

1

    

    



c

1

1 2

   

c







'  f

 2 4 2 1 1 1 v    



n

2 3 2 2 c c  

c d r dN  

1

  

(6)



c

1

  cr   





n

Eq. (7) can be written in the following simplified form:

d A B dN  

  m k m 

(7)

where parameter m is related to the Coffin-Manson parameter m as m=1/c+1 and

c A r 

(8)

2 3 2 2 c c  



k

(9)

 

    

 2 4 2 1 1 1 c v               cr 1 2





'  f



n

 

(10)

B

 

n



Parameters n΄, K cr , c, ε f ΄, Ε can be determined experimentally. Crack growth rate in Eq. (7) is dependent on parameter B, which includes material properties and therefore provides a physical background in the crack growth analysis. The only fitting parameter I Eq. (7) is length r c , which is also an undefined parameter in the SED theory.

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