Issue 30

P.N.B. Reis et alii, Frattura ed Integrità Strutturale, 30 (2014) 431-437; DOI: 10.3221/IGF-ESIS.30.52

According with Tab. 1, it is possible to observe that only a small decrease of the interlaminar fracture toughness occurs, around 7.5%, which means that the G IC parameter is practically independent of the initial delamination length. Therefore, for the present laminates, the average value of G IC is around 281 J/m 2 .

Initial crack length (a 0 )

30 mm

45 mm

50 mm

[J/m 2 ]

292.3

279.6

270.4

G IC

SD [J/m 2 ]

65.6

63.6

58.1

Table 1 : G IC

values versus delamination length.

Fig. 6 presents the energy release rate for mode II specimens and the formulation used to obtain G can be found in the work of Morais and Pereira [9]. Therefore, G IIC was calculated by the following equation:

2

2 e

.a 9.P

IIG 

(2)

2

3

.h .E 16.b

1

where P is the load, b is the specimen width, h is the specimen thickness, E 1 is the flexural modulus a e is expressed by the Eq. (3):

3

3

.



2.L .C b.h 8.E

3

1

f

a



(3)

e

3

where L is half of the spam length (50 mm) C f given by Eq. (4):

3.L

 

(4)

C C

f



10.

.b.h

13

where  13

 is the shear moduli C the specimen compliance expressed by Eq. (5):

3

3

)  

2.L

3.(a

3.L

II





(5)

C

. 

3

10

.b.h

.b.h 8.E

13

1

and, finally, for carbon fibers, Δ II

is expressed by the following equation:

13 72. 1E

h. 

(6)

II



435