PSI - Issue 17

Piotr Smarzewski / Procedia Structural Integrity 17 (2019) 5–12 Piotr Smarzewski / Structural Integrity Procedia 00 (2019) 000 – 000

10 6

a

b

Fig. 4. Typical experimental load-deflection curves of HPC with (a) 5% SF content; (b) 25% SF content.

The behaviour of HPC notched beam specimens during the bending test was linear up to the peak load. After that the curve drops until the specimen will break. The stress intensity factor K Ic , which expresses the stress field around the crack tip, was calculated to evaluate the crack resistance of HPC specimens with different SF content based on the equation given by Gettu and Shah (1994)

F

( )

p

1.5 (MN/m ) 

K

f

(1)

=

Ic

b h

where F p is the peak load, b is the specimen width, h is the specimen height, f ( α ) is the function of specimen geometry calculated as follows

) (

)

(

   

    

2   3/ 2 1.99 1 2.15 3.93 2.7   − − − +

( )

f

6  

= 

(2)

( ) ( 1 2 1 +

)

  −

where α is the relative length of the crack, α = a 0 / h , a 0 is the depth of the notch. The fracture energy G Ic is obtained on the notched beams in three-point bending as follows

2 (1 )  −

= G K

(N/mm)

Ic

(3)

Ic

E

c

where ν is the Poisson’s ratio, E c is the elastic modulus . The elastic-plastic failure parameter is designated, J Ic , was computed based on the experimental load-deflection curves

A

J

(N/mm)

=

(4)

Ic

− b h a

2 (

)

0

where A is the energy accumulated in the specimen up to reach peak load F p . Another parameter for the determination of fracture toughness in the elastic-plastic region is the crack tip opening displacement ( CTOD ). CTOD is the displacement at the original crack tip and the 90° intercept. The brittleness of HPC can be expressed by characteristic length l ch . The shorter the characteristic length the more brittle is the HPC. The characteristic length is defined according to the equation, Montgomery (1984)