PSI - Issue 2_A

Juan E Perez Ipiña et al. / Procedia Structural Integrity 2 (2016) 769–776 Author name / Structural Integrity Procedia 00 (2016) 000–000

771

3

b

    

    

  1 B

  

   

2 ( ) K K K K   0( ) B Jc B

min( ) B

1 exp     N

P

(3)

1

2

min( ) B

1

1

If B 2 specimens are tested, the corresponding failure probability, estimating the corresponding parameters, will be:

b

    

    

  2 B

  

   

2 ( ) K K K K   0( ) B Jc B

min( ) B

1 exp    

P

(4)

2

2

min( ) B

2

2

Working on Eqs. (2), (3) and (4), it is possible to predict the toughness and the K 0 parameter of B 2 specimens testing B 1 specimens, by means of Eqs. (5) and (6).

1

b

1 B       2 B





( 1 ) B

2 ( ) K K  JC B

1 ( ) K K  JC B



(5)

min( ) B

min( ) B

1

1

1

b

1 B       2 B





( 1 ) B

0( ) B K K 

1 0( ) B K K 



(6)

min( ) B

min( ) B

2

1

1

1.2. Master curve size conversion ASTM E1921-15a  1 (2015) sets up a procedure for K

0 determination. It includes calculating the values of K Jc , derived from Jc using Eq. (7), the conversion of these last values to 1-inch size equivalent, as well as specifications for data censoring.

. J E C

K



(7)

J

2

1





C

This standard imposes two limits for K Jc values: the first one is given by the condition of high crack-front constraint at fracture (Eq. (8)).

Eb



K



0

YS

(8)





max

J

2

30 1





The second limit states that K Jc values also shall be regarded as invalid for tests that terminate in cleavage after more than 0.05(W-a o ) or 1 mm (0.040 in.), whichever is smaller, of slow-stable crack growth. The obtained K Jc values for a B N thickness specimen must be converted to 1 inch equivalent by means of Eq. (5),

taking Kmin(B 2 ) = 20, b(B 2 ) =4 and B2 =1. K 0 is calculated by means of Eq. (9):